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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2014	Feb. 19, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	Clean Energy Fuels Corp.
Entity Central Index Key	0001368265
Document Type	10-K
Document Period End Date	Dec. 31, 2014
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 773,993,465
Entity Common Stock, Shares Outstanding		90,363,353
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 92,381	$ 240,033
Restricted cash	6,012	8,403
Short-term investments	122,546	138,240
Accounts receivable, net of allowance for doubtful accounts of $832 and $752 as of December 31, 2013 and December 30, 2014, respectively	81,970	53,473
Other receivables	56,223	26,285
Inventory	34,696	33,822
Prepaid expenses and other current assets	19,811	20,840
Total current assets	413,639	521,096
Land, property and equipment, net	514,269	487,854
Notes receivable and other long-term assets, net	71,904	73,697
Investments in other entities	6,510
Goodwill	98,726	88,548
Intangible assets, net	55,361	79,770
Total assets	1,160,409	1,250,965
Current liabilities:
Current portion of long-term debt and capital lease obligations	4,846	23,401
Accounts payable	43,922	33,541
Accrued liabilities	56,760	46,745
Deferred revenue	14,683	16,419
Total current liabilities	120,211	120,106
Long-term debt and capital lease obligations, less current portion	500,824	532,017
Long-term debt, related party	65,000	65,000
Other long-term liabilities	9,339	15,304
Total liabilities	695,374	732,427
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value. Authorized 1,000,000 shares; issued and outstanding no shares
Common stock, $0.0001 par value. Authorized 149,000,000 shares, issued and outstanding 89,364,397 shares at December 31, 2013; authorized 224,000,000 shares, issued and outstanding 90,203,344 shares at December 31, 2014	9	9
Additional paid-in capital	898,106	883,045
Accumulated deficit	(457,441)	(367,782)
Accumulated other comprehensive income (loss)	(3,248)	(700)
Total Clean Energy Fuels Corp. stockholders' equity	437,426	514,572
Noncontrolling interest in subsidiary	27,609	3,966
Total stockholders' equity	465,035	518,538
Total liabilities and stockholders' equity	$ 1,160,409	$ 1,250,965

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 752	$ 832
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, Authorized shares	1,000,000	1,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, Authorized shares	224,000,000	149,000,000
Common stock, issued shares	90,203,344	89,364,397
Common stock, outstanding shares	90,203,344	89,364,397

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Product revenues	$ 380,199	$ 310,813	$ 293,777
Service revenues	48,741	41,662	40,231
Total revenue	428,940	352,475	334,008
Cost of sales (exclusive of depreciation and amortization shown separately below):
Product cost of sales	291,462	213,593	236,471
Service cost of sales	17,325	11,169	17,213
Derivative gains:
Series I warrant valuation	(5,748)	(938)	(3,391)
Selling, general and administrative	126,435	138,024	117,976
Depreciation and amortization	49,058	42,318	36,261
Impairment of long-lived assets	4,772
Total operating expenses	483,304	404,166	404,530
Operating loss	(54,364)	(51,691)	(70,522)
Interest expense, net	(44,357)	(29,287)	(16,069)
Other income (expense), net	(2,571)	(970)	1,236
Impairment of cost method investment			(14,544)
Income (loss) from equity method investments	(490)	(76)	331
Gain from sale of equity method investment		4,705
Gain from sale of subsidiary	11,998	14,115
Loss before income taxes	(89,784)	(63,204)	(99,568)
Income tax (expense) benefit	(1,075)	(3,715)	(1,294)
Net loss	(90,859)	(66,919)	(100,862)
Loss (income) of noncontrolling interest	1,200	(49)	(393)
Net loss attributable to Clean Energy Fuels Corp.	$ (89,659)	$ (66,968)	$ (101,255)
Loss per share:
Basic and diluted (in dollars per share)	$ (0.96)	$ (0.71)	$ (1.16)
Weighted average common shares outstanding:
Basic and diluted (in shares)	93,678,432	93,958,758	87,455,073

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income (loss)	$ (90,859)	$ (66,919)	$ (100,862)
Other comprehensive income, net of tax:
Foreign currency translation adjustments	(7,958)	(1,680)	4,030
Foreign currency adjustments on intra-entity long-term investments	4,866	(4,834)	1,218
Unrealized gains (losses) on available-for sale securities	544	(445)	(32)
Unrecognized gains on derivatives		108	2,151
Total other comprehensive income (loss), net of tax	(2,548)	(6,851)	7,367
Comprehensive income (loss)	(93,407)	(73,770)	(93,495)
Clean Energy Fuels Corp
Net income (loss)	(89,659)	(66,968)	(101,255)
Other comprehensive income, net of tax:
Foreign currency translation adjustments	(7,958)	(1,680)	4,030
Foreign currency adjustments on intra-entity long-term investments	4,866	(4,834)	1,218
Unrealized gains (losses) on available-for sale securities	544	(445)	(32)
Unrecognized gains on derivatives		108	2,151
Total other comprehensive income (loss), net of tax	(2,548)	(6,851)	7,367
Comprehensive income (loss)	(92,207)	(73,819)	(93,888)
Noncontrolling Interest in Subsidiary
Net income (loss)	(1,200)	49	393
Other comprehensive income, net of tax:
Comprehensive income (loss)	$ (1,200)	$ 49	$ 393

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stock	Additional-Paid In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiary	Total
Balance at Dec. 31, 2011	$ 9	$ 741,650	$ (199,559)	$ (1,216)	$ 3,524	$ 544,408
Balance (in shares) at Dec. 31, 2011	85,433,258
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options		8,969				8,969
Issuance of common stock upon exercise of options (in shares)	1,568,480
Issuance of common stock, net of offering costs		8,503				8,503
Issuance of common stock, net of offering costs (in shares)	632,740
Issuance of warrants in connection with the Credit Agreement		56,158				56,158
Stock-based compensation		22,087				22,087
Net income (loss)			(101,255)		393	(100,862)
Accumulated other comprehensive income (loss)				7,367		7,367
Balance at Dec. 31, 2012	$ 9	837,367	(300,814)	6,151	3,917	546,630
Balance (in shares) at Dec. 31, 2012	87,634,478
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options		677				677
Issuance of common stock upon exercise of options (in shares)	119,349
Issuance of common stock, net of offering costs		21,993				21,993
Issuance of common stock, net of offering costs (in shares)	1,610,570
Stock-based compensation		23,008				23,008
Net income (loss)			(66,968)		49	(66,919)
Accumulated other comprehensive income (loss)				(6,851)		(6,851)
Balance at Dec. 31, 2013	$ 9	883,045	(367,782)	(700)	3,966	$ 518,538
Balance (in shares) at Dec. 31, 2013	89,364,397					89,364,397
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options		1,771				$ 1,771
Issuance of common stock upon exercise of options (in shares)	483,863
Issuance of common stock in connection with ESPP		529				529
Issuance of common stock in connection with ESPP (in shares)	35,745
Issuance of common stock, net of offering costs		3,750				3,750
Issuance of common stock, net of offering costs (in shares)	319,339
Exercise of additional membership interest in subsidiary		2,363				2,363
Stock-based compensation		11,514				11,514
Foreign currency adjustments on intra-entity long-term investments converted to equity		(4,866)				(4,866)
Acquisition of non-controlling interest in subsidiary					28,075	28,075
Sale of non-controlling interest in subsidiary					(3,232)	(3,232)
Net income (loss)			(89,659)		(1,200)	(90,859)
Accumulated other comprehensive income (loss)				(2,548)		(2,548)
Balance at Dec. 31, 2014	$ 9	$ 898,106	$ (457,441)	$ (3,248)	$ 27,609	$ 465,035
Balance (in shares) at Dec. 31, 2014	90,203,344					90,203,344

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	$ (90,859)	$ (66,919)	$ (100,862)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	49,058	42,318	36,261
Impairment of cost method investment			14,544
Provision for doubtful accounts and notes	1,277	1,962	1,358
Series I warrant valuation	(5,748)	(938)	(3,391)
Stock-based compensation expense	11,514	23,008	22,087
Amortization of debt issuance cost	4,194	1,662	551
Accretion of notes payable	412	1,140	2,016
Gain on sale of equity method investment		(4,705)
Dividend received on equity method investment		1,091
Long-lived intangible impairment	4,772
Gain on sale of subsidiary	(11,998)	(14,115)
Gain on contingent consideration for acquisitions	(208)	(1,132)	(4,112)
Changes in operating assets and liabilities, net of assets and liabilities acquired:
Accounts and other receivables	(55,573)	(441)	1,832
Inventory	(979)	(637)	(1,879)
Margin deposits on futures contracts			3,000
Prepaid expenses and other assets	1,361	579	4,201
Accounts payable	9,126	(6,962)	(328)
Accrued expenses and other	7,646	19,395	4,966
Net cash used in operating activities	(76,005)	(4,694)	(19,756)
Cash flows from investing activities:
Purchases of short-term investments	(157,629)	(170,935)	(55,062)
Maturities and sales of short-term investments	171,902	93,289	49,504
Purchases of property and equipment	(86,235)	(86,730)	(192,894)
Loans made to customers	(9,140)	(3,950)	(10,521)
Payments on and proceeds from sales of loans receivable	6,580	4,153	8,251
Restricted cash	(3,567)	13,250	37,943
Cash received with sale of subsidiary, net of cash transferred	39,760	(1,178)
Deposits on equipment	(2,393)
Investments in other entities	(6,634)		(1,437)
Proceeds from sale of equity method investment		6,119
Acquisitions, net of cash acquired	467	(9,000)	269
Net cash used in investing activities	(46,889)	(154,982)	(163,947)
Cash flows from financing activities:
Proceeds from issuance of common stock and exercise of stock options	2,300	677	8,969
Proceeds from debt instruments	12,778	300,559	50,612
Proceeds from debt, related party		15,000
Proceeds from revolving line of credit	34,607	31,527	39,164
Proceeds from exercise of additional membership interest in subsidiary	6,992
Repayment of borrowings under revolving line of credit	(40,354)	(37,767)	(34,735)
Repayment of capital lease obligations and debt instruments	(41,036)	(10,147)	(10,040)
Contingent consideration paid relating to business acquisitions	(176)		(350)
Payment for debt issuance costs	(896)	(9,130)
Net cash provided (used) by financing activities	(25,785)	290,719	53,620
Effect of exchange rates on cash and cash equivalents	1,027	468	480
Net increase (decrease) in cash and cash equivalents	(147,652)	131,511	(129,603)
Cash and cash equivalents, beginning of year	240,033	108,522	238,125
Cash and cash equivalents, end of year	92,381	240,033	108,522
Supplemental disclosure of cash flow information:
Income taxes paid	943	2,228	1,160
Interest paid, net of $6,304, $2,517 and $3,160 capitalized, respectively	$ 39,224	$ 22,110	$ 13,994

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Consolidated Statements of Cash Flows
Interest paid, capitalized	$ 3,160	$ 2,517	$ 6,304

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2014

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

(1) Summary of Significant Accounting Policies

The Company

Clean Energy Fuels Corp., together with its majority and wholly owned subsidiaries (hereinafter collectively referred to as the "Company," unless the context of the use of the term indicates or requires otherwise) is engaged in the business of selling natural gas fueling solutions to its customers, primarily in the United States and Canada.

The Company has a broad customer base in a variety of markets, including trucking, airports, taxis, refuse, ready mix, and public transit. The Company owns, operates, maintains and/or supplies over 540 natural gas fueling stations within the United States and Canada. The Company generates revenue through selling compressed natural gas ("CNG") and liquefied natural gas ("LNG"), providing operation and maintenance ("O&M") services to customers, building and selling natural gas fueling stations to customers, manufacturing and servicing non-lubricated natural gas fueling compressors and other equipment for CNG and LNG fueling stations, offering assessment, design and modification solutions to provide operators with code-compliant service and maintenance facilities for natural gas vehicle fleets, processing and selling renewable natural gas ("RNG"), financing customers' vehicle purchases and selling tradable credits the Company generates by selling natural gas and RNG as a vehicle fuel, including credits ("LCFS Credits") under the California low carbon fuel standard and Renewable Identification Numbers ("RIN Credits") under the federal Renewable Fuel Standard Phase 2. In addition, through June 28, 2013, the Company provided natural gas vehicle conversions and design and engineering services for natural gas engine systems (see note 2).

Basis of Presentation

The consolidated financial statements include the accounts of the Company and its subsidiaries, and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to state fairly the Company's financial position, results of operations and cash flows in accordance with U.S. generally accepted accounting principles ("US GAAP"). All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and revenues and expenses recorded during the reporting periods. Actual results could differ from those estimates. Significant estimates made in preparing the consolidated financial statements include (but are not limited to) those related to revenue recognition, warranty reserves, goodwill and long-lived intangible asset valuations and impairment assessments, income tax valuations, and stock-based compensation expenses.

Cash and Cash Equivalents

The Company considers all highly liquid investments with maturities of three months or less on the date of acquisition to be cash equivalents.

Fair Value of Financial Instruments

The carrying values of the Company's financial instruments, including cash and cash equivalents, short-term investments, accounts and other receivables, notes receivable, accounts payable, accrued expenses and other current liabilities, capital lease obligations and notes payable approximate fair value.

Inventories

Inventory consists of work in process and finished goods and is stated at the lower of cost (first-in, first-out) or market. The Company writes down the carrying value of its inventory to net realizable value for estimated obsolescence or unmarketable inventory in an amount equal to the difference between the cost of inventory and its estimated realizable value based upon assumptions about future demand and market conditions, among other factors.

Inventories consisted of the following as of December 31, 2013 and 2014:

	2013		2014
Raw materials and spare parts	$	30,521	$	31,389
Work in process		3,011		3,292
Finished goods		290		15

Total	$	33,822	$	34,696

Property and Equipment

Property and equipment are recorded at cost. Depreciation and amortization are recognized over the estimated useful lives of the assets using the straight-line method. The estimated useful lives of depreciable assets are 20 years for LNG liquefaction plant assets, 10 years for station equipment and LNG trailers, and three to seven years for all other depreciable assets. Leasehold improvements are amortized over the shorter of their estimated useful lives or related lease terms. Periodically, the Company receives grant funding to assist in the financing of natural gas fueling station construction. The Company records the grant proceeds as a reduction of the cost of the respective asset. Total grant proceeds received were approximately $5,908, $3,114, and $959 for the years ended December 31, 2012, 2013, and 2014 respectively.

Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. Recoverability of long-lived assets to be held and used is measured by a comparison of the carrying amount of an asset to future net undiscounted cash flows expected to be generated by the asset or asset group. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the fair value of the assets.

Goodwill and Intangible Assets

Goodwill represents the excess of costs incurred over the fair value of the net assets of acquired businesses. Goodwill and intangible assets acquired in a business combination and determined to have an indefinite useful life are not amortized. The Company assesses its goodwill and indefinite lived intangible assets for impairment annually on October 1, or more frequently if a triggering event occurs between impairment testing dates. The Company's impairment assessment begins with a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. The qualitative assessment includes assessing the potential impact on a reporting unit's fair value of certain events and circumstances, including the Company's market capitalization value, macroeconomic conditions, industry and market considerations, cost factors, and other relevant entity-specific events. If it is determined, based upon the qualitative assessment, that it is more likely than not that the reporting unit's fair value is less than its carrying amount, then a two-step quantitative impairment test is performed. A qualitative assessment is an option available on an individual reporting unit basis and is an unconditional alternative to Step 1 of the goodwill impairment test. A reporting entity can choose to perform either Step 1 or a qualitative assessment in subsequent reporting periods. If the Company does conduct a Step 1 test, the Company looks at its projected future cash flows and its market capitalization for its respective operations. In these instances, to the extent the Company's projected future cash flows do not materialize as planned or its market capitalization decreases, the Company could be forced to take an impairment charge in future periods.

The Company tests tangible and intangible long -lived assets with definite useful lives for impairment whenever circumstances or events may affect the recoverability of the long -lived assets. The evaluation is primarily dependent on the estimated future cash flows of the assets and the fair value of these items, as determined by management based on a number of estimates, including future cash flow projections, discount rates and terminal values. In determining these estimates, management considers internally generated information and information obtained from discussions with market participants. The determination of fair value requires significant judgment by both management and outside experts engaged to assist in this process. There were no impairment charges for goodwill or indefinite-lived intangible assets resulting from the October 1, 2012, 2013 or 2014 impairment testing. The Company reduced its goodwill balance by $774 and $7,205 when it sold BAF and its interest in DCE and its subsidiary DCEMB on June 28, 2013 and December 29, 2014, respectively, and added $16,555 and $21,070 to its goodwill balance when it acquired MGES and NG Advantage on May 6, 2013 and October 14, 2014, respectively (all as defined and described in note 2). The goodwill balances on the consolidated balance sheets include foreign currency translation gains (losses) of $(3,098) and $(3,687) as of December 31, 2013 and 2014, respectively.

Intangible assets with finite useful lives are amortized over their respective estimated useful lives using the straight-line method. The estimated useful lives of intangible assets with finite useful lives are two to 20 years for technology, one to 16 years for lease agreements, one to eight years for customer relationships, one to 10 years for acquired contracts, two to 20 years for trademarks and trade names, and three years for non-compete agreements. The intangible assets with finite useful lives are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value of the asset may not be recoverable. In connection with the acquisition of the controlling interest in NG Advantage, the Company allocated approximately $5,600 of the purchase price to the identifiable intangible assets related to customer relationships and trade names that were acquired with the acquisition. In the fourth quarter of 2014, the Company determined that a long-lived asset related to a contract acquired in its acquisition of the assets of IMW Industries, Ltd. ("IMW") was impaired. Accordingly, the Company recorded an impairment charge of $4,772 related to this intangible asset.

The Company's intangible assets as of December 31, 2013 and 2014 were as follows:

	2013			2014
Technology	$	54,400		$	54,400
Lease agreements		21,045			—
Customer relationships		12,791			16,430
Acquired contracts		13,121			3,694
Trademark and trade names		6,700			8,200
Non-compete agreements		2,126			2,060

Total intangible assets		110,183			84,784
Less accumulated amortization		(30,003	)		(24,384	)
Foreign currency rate change		(410	)		(5,039	)

Net intangible assets	$	79,770		$	55,361

Included above is a trademark of indefinite useful life with a carrying value of $1,200 as of December 31, 2013 and 2014.

Amortization expense for intangible assets was $10,875, $9,016, and $7,024 for the years ended December 31, 2012, 2013 and 2014, respectively. Estimated amortization expense for the five years and thereafter succeeding the year ended December 31, 2014 is approximately $5,130, $5,130, $4,916, $4,366, $3,465 and $32,354 respectively.

Warranty Liability

The Company records warranty liabilities at the time of sale for the estimated costs that may be incurred under its standard warranty. Changes in the warranty liability are presented in the following table:

	December 31, 2013			December 31, 2014
Warranty liability at beginning of year	$	2,665		$	2,545
Costs accrued for new warranty contracts and changes in estimates for pre-existing warranties		3,551			3,746
Service obligations honored		(3,089	)		(3,989	)
Sale of subsidiary		(582	)		—

Warranty liability at end of year	$	2,545		$	2,302

Asset Retirement Obligations

The Company recognizes the fair value of a liability for an asset retirement obligation in the period in which the liability is incurred or becomes reasonably estimable and if there is a legal obligation to restore or remediate the property at the end of the asset life or at the end of the lease term. The liability amounts are based upon future retirement cost estimates and incorporate many assumptions such as the costs to restore the property, future inflation rates, and the adjusted risk free rate of interest. When the liability is initially recorded, the Company capitalizes the cost by increasing the related property and equipment balance. Over time, the liability is increased and expense is recognized for the change in the present value of the obligation, and the initial capitalized cost is depreciated over the useful life of the asset.

The following table summarizes the activity of the asset retirement obligation, of which $1,322 and $1,603 is included in other long-term liabilities, with the remaining current portion included in accrued liabilities, as of December 31, 2013 and 2014, respectively:

	2013			2014
Beginning balance	$	1,313		$	1,461
Liabilities incurred		89			118
Liabilities settled		(5	)		—
Accretion expense		64			59

Ending balance	$	1,461		$	1,638

Revenue Recognition

The Company recognizes revenue on natural gas sales and O&M services in accordance with US GAAP, which requires that four basic criteria must be met before revenue can be recognized: (i) persuasive evidence of an arrangement exists; (ii) delivery has occurred and title and the risks and rewards of ownership have been transferred to the customer or services have been rendered; (iii) the price is fixed or determinable; and (iv) collectability is reasonably assured. Applying these factors, the Company typically recognizes revenue from the sale of natural gas fuel at the time the fuel is dispensed or, in the case of LNG sales agreements, delivered to the customers' storage facilities. The Company recognizes revenue from O&M agreements as the related services are provided.

In certain transactions with its customers, the Company agrees to provide multiple products or services, including construction of a station, providing O&M services to the station, and sale of fuel to the customer. The Company evaluates the separability of revenues based on Financial Accounting Standards Board ("FASB") authoritative guidance, which provides a framework for establishing whether or not a particular arrangement with a customer has one or more revenue elements, and allows the Company to use a combination of internal and external objective and reliable evidence to develop management's best estimate of the fair value of the contract elements. If the arrangement contains a lease, the Company uses the existing evidence of fair value to separate the lease from the other elements in the arrangement. The arrangement's consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the estimated relative selling price of each deliverable, which is determined based on the historical data derived from the Company's stand-alone projects. The revenue allocated to the construction of the station is recognized using the completed-contract method. The revenue allocated to the O&M services is recognized ratably over the term of the arrangement and sale of fuel is recognized as the fuel is delivered.

The Company recognizes revenue related to its leasing activities in accordance with FASB authoritative guidance. The Company's existing station leases are sales-type leases, giving rise to profit at the delivery of the leased station. Unearned revenue is amortized into income over the life of the lease using the effective-interest method. For these arrangements, the Company recognizes gas sales and O&M service revenues as earned from the customer on a volume-delivered basis.

The Company typically recognizes revenue on fueling station construction projects where it sells the station to the customer using the completed-contract method because the projects are short-term and the results of operations reported on the completed-contract basis would not vary materially from those resulting from the use of the percentage-of-completion method. The construction contract is considered to be substantially completed at the earlier of customer acceptance of the fueling station or the time when the fuel dispensing activities begin. When applicable, multi-station construction contracts are segmented into phases as negotiated with customers. Gross margin related to each phase is recognized when it is substantially complete. IMW and Wyoming Northstar Incorporated, Southstar, LLC, and M&S Rental LLC (Wyoming Northstar Incorporated, Southstar, LLC, and M&S Rental LLC are collectively referred to as "Northstar") use the percentage-of-completion method of accounting to recognize revenue because their projects are small and they have been able to demonstrate that they can reasonably estimate costs to complete. In these circumstances, revenue is recognized based on costs incurred in relation to total estimated costs to be incurred for a project.

The Company generates LCFS Credits when it sells RNG and conventional natural gas for use as a vehicle fuel in California, and it generates RIN Credits when it sell RNG for use as a vehicle fuel. The Company can sell these credits to third parties who need the RIN Credits and LCFS Credits to comply with federal and state emission requirements. The Company recognizes revenue from the generation of these credits at the time the Company has an agreement in place to sell the credits at a fixed or determinable price.

Alternative Fuels Excise Tax Credit

From October 1, 2006 through December 31, 2011, the Company was eligible to receive a federal fuel tax credit ("VETC") of $0.50 per gasoline gallon equivalent of CNG and $0.50 per liquid gallon of LNG that it sold as vehicle fuel. Based on the service relationship with its customers, either the Company or its customers claimed the credit. The Company records its VETC credits as revenue in its consolidated statements of operations as the credits are fully refundable and do not need to offset income tax liabilities to be received. The American Taxpayer Relief Act, signed into law on January 2, 2013, reinstated VETC for calendar year 2013 and also made it retroactive to January 1, 2012. The Company did not record any VETC revenues in 2012, but VETC revenues recognized in 2013 were $45,439, which included $20,800 for CNG and LNG the Company sold in 2012 that was recognized in January 2013 when the legislation was signed into law. The Tax Increase Prevention Act, signed into law on December 19, 2014, reinstated VETC for calendar year 2014. VETC revenues recognized in December 2014 for the 2014 calendar year were $28,359.

LNG Transportation Costs

The Company records the costs incurred to transport LNG to its customers in the line item cost of sales in the accompanying statements of operations.

Advertising Costs

Advertising costs are expensed as incurred. Advertising costs amounted to $1,340, $1,391, and $439 for the years ended December 31, 2012, 2013, 2014 respectively.

Stock-Based Compensation

The Company recognizes compensation expense for all stock-based payment arrangements, net of an estimated forfeiture rate, over the requisite service period of the award. For stock options, the Company determines the grant date fair value using the Black-Scholes option pricing model, which requires the input of certain assumptions, including the expected life of the stock-based payment awards, stock price volatility and risk-free interest rates. For restricted stock units, the Company determines the grant date fair value based on the closing market price of its common stock on the date of grant.

Foreign Currency Translation

In accordance with FASB authoritative guidance, the Company uses the local currency as the functional currency of its foreign subsidiaries. Accordingly, all assets and liabilities outside the United States are translated into U.S. dollars at the rate of exchange in effect at the balance sheet date. Revenue and expense items are translated at the weighted-average exchange rates prevailing during the period. Net foreign currency translation adjustments are recorded as accumulated other comprehensive income (loss) in stockholders' equity.

Foreign currency transactions occur when there is a transaction denominated in other than the respective entity's functional currency. The Company records the changes in the exchange rate for these transactions in the consolidated statements of operations. For the fiscal years ended December 31, 2012, 2013 and 2014, foreign exchange transaction gains and (losses) were included in other income (expense) and were $678, $(1,196), and $(3,188) respectively.

Income Taxes

Income taxes are computed using the asset and liability method. Under this method, deferred income taxes are recognized by applying enacted statutory tax rates applicable to future years to differences between the tax bases and financial carrying amounts of existing assets and liabilities. Valuation allowances are established when it is more likely than not that such deferred tax assets will not be realized.

The Company has a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities based on the technical merits of the position. The amount recognized is measured as the largest amount of benefit that has a greater than 50 percent likelihood of being realized upon ultimate settlement. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefit in income tax expense.

Net Loss Per Share

Basic net loss per share is computed by dividing net loss attributable to Clean Energy Fuels Corp. by the weighted-average number of common shares outstanding and common shares issuable for little or no cash consideration during the period. Diluted net loss per share is computed by dividing net loss attributable to Clean Energy Fuels Corp. by the weighted-average number of common shares outstanding and common shares issuable for little or no cash consideration and potentially dilutive securities outstanding during the period. Potentially dilutive securities include stock options, warrants, convertible notes and restricted stock units. The dilutive effect of stock options and warrants is computed under the treasury stock method. The dilutive effect of convertible notes and restricted stock units is computed under the if-converted method. Potentially dilutive securities are excluded from the computations of diluted net loss per share if their effect would be antidilutive. In 2013, 5,000,000 shares of common stock related to the GE Warrant, as defined and described in notes 9 and 11, were included in the basic and dilutive net loss per share calculation. On September 11, 2014, the Company determined it no longer met certain conditions required to include 4,000,000 shares of common stock related to the GE Warrant in its weighted average share calculations. As a result, from September 11, 2014 the Company (i) excluded 4,000,000 shares of common stock issuable upon exercise of the GE Warrant from the weighted average number of shares outstanding in the basic and diluted net loss per share calculations, and (ii) included the remaining 1,000,000 shares of common stock issuable upon exercise of the GE Warrant in the basic and diluted net loss per share calculations, as 500,000 shares were exercisable in 2012 as of the execution of the associated Credit Agreement, as defined and described in note 9, and an additional 500,000 shares became exercisable on December 31, 2014 in connection with the amendment to the Credit Agreement on December 29, 2014.

The following potentially dilutive securities have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive:

	2012		2013		2014
Stock options		12,083,677		11,526,998		11,486,301
Warrants		2,130,682		2,130,682		6,130,682
Convertibles notes		16,262,226		35,185,979		35,185,979
Restricted stock units		1,545,000		1,590,836		2,591,752

Comprehensive Income (Loss)

Comprehensive income (loss) is defined as the change in equity (net assets) of a business enterprise during the period from transactions and other events and circumstances from non-owner sources. The difference between net income and comprehensive income for the years ended December 31, 2012, 2013, and 2014 was primarily comprised of the Company's foreign currency translation adjustments and unrealized gains (losses) on futures contracts. During 2014, the Company converted a long-term equity intra-entity investment to equity and the related translation adjustments were reclassified to additional paid-in capital.

Concentration of Credit Risk

Credit is extended to all customers based on financial condition, and collateral is generally not required. Concentrations of credit risk with respect to trade receivables are limited because of the large number of customers comprising the Company's customer base and dispersion across many different industries and geographies. However, certain international customers have historically been slower to pay on trade receivables. Accordingly, the Company continuously monitors collections and payments from its customers and maintains a provision for estimated credit losses based upon its historical experience and any specific customer collection issues that it has identified. In addition, through Export Development Canada, IMW maintains accounts receivable insurance on a substantial portion of its foreign trade receivables, which covers up to 90% of the related outstanding balance. Although credit losses have historically been within the Company's expectations and the provisions established, the Company cannot guarantee that it will continue to experience the same credit loss rates that it has in the past.

The Company places its cash and cash equivalents with high credit quality financial institutions. At times, such investments may be in excess of the Federal Deposit Insurance Corporation ("FDIC"), Canadian Deposit Insurance Corporation ("CDIC"), and other foreign insurance limits. Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash deposits. The amounts in excess of FDIC insurance limits were $237,004 and $88,740 as of December 31, 2013 and 2014, respectively.

Recently Adopted Accounting Changes and Recently Issued and Adopted Accounting Standards

On April 10, 2014, the Company adopted Accounting Standards Update ("ASU") No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360), Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. The ASU provides new guidance that raises the threshold for disposals to qualify as discontinued operations by focusing on strategic shifts that have or will have a major effect on an entity's operations and financial results. The guidance allows companies to have significant continuing involvement and continuing cash flows with the disposed component. The Company early adopted this standard. On December 29, 2014, the Company disposed of its 51% ownership in its subsidiary DCE (as defined in note 2), which was not material to the operations and financial results nor a strategic shift of the Company. See note 2 for further discussion.

On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The guidance is effective for annual and interim reporting periods beginning after December 15, 2016, with early adoption prohibited. The Company is currently evaluating the impact this ASU will have on its consolidated financial statements.

On August 27, 2014, the FASB issued ASU No. 2014-15, to communicate amendments to FASB Account Standards Codification Subtopic 205-40, "Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern." The ASU requires management to evaluate relevant conditions, events and certain management plans that are known or reasonably knowable as of the evaluation date when determining whether substantial doubt about an entity's ability to continue as a going concern exists. Management will be required to make this evaluation for both annual and interim reporting periods. Management will need to make certain disclosures if it concludes that substantial doubt exists or when it plans to alleviate substantial doubt about the entity's ability to continue as a going concern. The standard is effective for annual periods ending after December 15, 2016 and for interim reporting periods starting in the first quarter of 2017. Early adoption is permitted. The Company does not expect the adoption of the guidance to have a material impact on its consolidated financial statements.

Acquisitions and Divestitures

12 Months Ended

Dec. 31, 2014

Acquisitions and Divestitures

Acquisitions and Divestitures

(2) Acquisitions and Divestitures

BAF

On June 28, 2013, the Company, entered into and closed a stock purchase agreement (the "BAF Sale Agreement") with Westport Innovations Inc. ("Westport") and Westport Innovations (U.S.) Holdings Inc., a wholly owned subsidiary of Westport (together with Westport, the "Westport Parties"). Under the terms of the BAF Sale Agreement, on June 28, 2013, the Westport Parties purchased all of the outstanding capital stock of BAF Technologies, Inc. ("BAF"), including BAF's 100% ownership interest of ServoTech Engineering, Inc., for 816,460 shares of Westport's common stock. Pursuant to the BAF Sale Agreement, the Company was issued 718,485 shares of Westport's common stock on June 28, 2013 and 97,975 shares of Westport's common stock (the "Holdback Shares") were retained by Westport for one year as security for the Company's indemnification obligations under the BAF Sale Agreement. At the end of June 2014, the Company was issued 94,914 of the Holdback Shares, with the remaining 3,061 Holdback Shares remaining unissued as a result of, and in full satisfaction of, an indemnity claim under the BAF Sale Agreement. In July 2013, the Company sold the 718,485 shares it initially received for net proceeds of $23,722. In July 2014, the Company sold all of the Holdback Shares it received for net proceeds of $1,727. Further, during August 2013, the Westport Parties repaid $2,478 of certain intercompany indebtedness of BAF to the Company following the conclusion of applicable post-closing adjustment procedures contemplated in the BAF Sale Agreement.

The fair value of the 816,460 shares of Westport's common stock on June 28, 2013 was $27,221, and the Company recognized an initial gain of $15,498 on June 28, 2013 related to the transaction. In December 2013, the Company wrote down the value of the Holdback Shares by $1,383, which resulted in an adjusted gain of $14,115 on the transaction. In July 2014, the Company wrote down the value of the Holdback Shares by an additional $122, which resulted in an adjusted gain of $13,993 on the transaction. The value of the shares received has been excluded from the Company's consolidated statements of cash flows as it is a non-cash investing activity. The gain was recorded in the line item gain from sale of subsidiary in the Company's consolidated statements of operations.

In addition, pursuant to the BAF Sale Agreement, the Company, Westport Power Inc. and Westport Fuel Systems Inc. (Westport Power, Inc. and Westport Fuel Systems, Inc. are collectively referred to as the "Westport Affiliates") entered into a marketing agreement, dated June 28, 2013, whereby the Westport Affiliates agreed to pay the Company $5,000 in cash, which was received on February 27, 2014. Under the marketing agreement, the Company and the Westport Affiliates agreed to collaborate during a two year period to encourage sales of all BAF products and certain vehicle products offered by the Westport Affiliates, and the Company agreed to provide 750,000 complimentary gasoline gallon equivalents of CNG to be used by the Westport Affiliates as marketing incentives. Additionally, the marketing agreement provides for the Company's appointment of a product line manager for BAF, and at least one member of a newly established operating committee formed to create sales and marketing strategies for BAF and assist in BAF's performance of these strategies.

MGES

On May 6, 2013, the Company entered into and closed a stock purchase agreement with Mansfield Energy Corp. ("Mansfield") and its wholly owned subsidiary Mansfield Gas Equipment Systems Corporation ("MGES"). MGES is primarily engaged in the business of providing CNG station design and construction and CNG equipment repair and maintenance services. Under the terms of the stock purchase agreement, the Company purchased from Mansfield all of the outstanding capital stock of MGES for $20,000, payable 50% in cash and 50% in shares of the Company's common stock. Upon closing, the Company delivered $9,000 in cash and 761,545 shares of the Company's common stock, and retained $1,000 as security for Mansfield's indemnification obligations under the stock purchase agreement. On the first anniversary of the closing date, the Company delivered the retained amount of $1,000 to Mansfield. In addition, in August 2013, the Company paid Mansfield an additional $563 following the conclusion of applicable post-closing adjustment procedures contemplated by the stock purchase agreement. The fair value of the Company's common stock delivered to Mansfield is excluded from the Company's consolidated statements of cash flows as it is a non-cash investing activity. The Company filed with the Securities and Exchange Commission a registration statement covering the resale of such shares, and the registration statement was declared effective in August 2013.

The Company accounted for this acquisition in accordance with FASB authoritative guidance for business combinations, which requires the Company to recognize the assets acquired and the liabilities assumed, measured at their fair values, as of the date of acquisition. The following table summarizes the allocation of the aggregate purchase price to the fair value of the assets acquired and liabilities assumed:

Current assets	$	4,475
Property, plant and equipment		1,369
Identifiable intangible assets		600
Goodwill		16,555

Total assets acquired		22,999
Current liabilities assumed		(1,984	)

Total purchase price	$	21,015

Management allocated approximately $600 of the purchase price to the identifiable intangible assets related to customer relationships and project back-orders that were acquired with the acquisition. The fair value of the identifiable intangible assets will be amortized on a straight-line basis over the estimated useful lives of such assets ranging from one to six years. The excess of the purchase price over the fair value of net assets acquired was allocated to goodwill, which primarily represents additional market share available to the Company as a result of the acquisition, and is fully deductible for income tax purposes.

The results of operations of MGES have been included in the Company's consolidated financial statements since May 6, 2013. The historical results of MGES's operations were not material to the Company's financial position or historical results of operations.

NG Advantage

On October 14, 2014, the Company entered a Common Unit Purchase Agreement ("UPA") with NG Advantage, LLC ("NG Advantage"). NG Advantage is engaged in the business of transporting CNG in high-capacity trailers to large industrial and institutional energy users, such as hospitals, food processors, manufacturers and paper mills, which do not have direct access to natural gas pipelines. The Company viewed the acquisition as a strategic investment in the expansion of the Company's initiative to deliver natural gas to industrial and institutional energy users. Under the terms of the UPA, the Company paid NG Advantage $37,650 for a 53.3% controlling interest in NG Advantage. $19,000 of the purchase price was paid in cash on October 14, 2014 and the remaining $18,650 of the purchase price was paid in the form of an unsecured promissory note issued by the Company (the "NG Advantage Note"). The principal amount of the NG Advantage Note is payable by the Company in two payments as follows: (i) $3,000 was paid January 13, 2015 and (ii) the remaining $15,650 is due no later than April 1, 2015. The NG Advantage Note does not bear interest. The fair value of the NG Advantage Note delivered to NG Advantage is excluded from the Company's consolidated statements of cash flows as it is a non-cash investing activity. The consideration paid is accounted for as an intercompany transaction, as NG Advantage's financial results are included in the Company's consolidated financial statements.

The Company accounted for this acquisition in accordance with FASB authoritative guidance for business combinations, which requires the Company to recognize the assets acquired and the liabilities assumed, measured at their fair values, as of the date of acquisition. The following table summarizes the allocation of the aggregate purchase price to the preliminary fair value of the assets acquired and liabilities assumed:

Current assets	$	40,558
Property, plant and equipment		20,862
Other long-term assets		5,115
Identifiable intangible assets		5,600
Goodwill		21,070

Total assets acquired		93,205
Current liabilities assumed		(9,165	)

Long-term debt including capital leases assumed, excluding current installments		(17,604	)
Other liabilities		(711	)

Non-controlling interest		(28,075	)

Total purchase price	$	37,650

In connection with its purchase of a controlling interest in NG Advantage, the Company assumed debt of $20,439 on a consolidated basis related to purchases of capital assets and working capital needs. Immediately after the Company's purchase of the controlling interest, $10,361 of such debt was paid with proceeds of the Company's investment in NG Advantage, and the related debt instruments were cancelled.

Management allocated approximately $5,600 of the purchase price to the identifiable intangible assets related to customer relationships and trade names that were acquired with the acquisition. The fair value of the identifiable intangible assets will be amortized on a straight-line basis over the estimated useful lives of such assets ranging from four to seven years. The excess of the purchase price over the fair value of net assets acquired was allocated to goodwill, which primarily represents additional market share available to the Company as a result of the acquisition, and is fully deductible for income tax purposes.

Management determined the fair value of the non-controlling interest to be $28,075 using a market approach and using inputs that included use of a comparable transaction to calculate the value of the non-controlling interest adjusted for a control premium.

The results of NG Advantage's operations have been included in the Company's consolidated financial statements since October 14, 2014. The historical results of NG Advantage's operations were not material to the Company's financial position or historical results of operations.

DCE and DCEMB

On September 4, 2014, Mavrix, LLC ("Mavrix"), a wholly owned subsidiary of the Company, sold to Cambrian Energy McCommas Bluff III LLC ("Cambrian") 19% of its then-70% interest in Dallas Clean Energy, LLC ("DCE"). On December 29, 2014, Mavrix entered into a Membership Interest Purchase Agreement (the "Agreement") with Cambrian, pursuant to which Mavrix sold to Cambrian its entire remaining 51% interest in DCE. DCE owns all of the equity interests in Dallas Clean Energy McCommas Bluff, LLC ("DCEMB"), which owns a renewable natural gas extraction and processing project at the McCommas Bluff landfill in Dallas, Texas. As consideration for the sale of DCE, the Company, through Mavrix, received $6,992 in cash in September 2014 and $40,588 in cash in December 2014 and may receive up to an additional $3,000 in cash on or before August 14, 2015, subject to the results of certain performance tests to be performed at the McCommas Bluff project on or before August 1, 2015 in accordance the terms of the Agreement. Prior to December 29, 2014, Cambrian owned a 49% interest in DCE. The Company will continue to have the right to market and sell biomethane produced at the McCommas Bluff project under its Redeem™ renewable natural gas vehicle fuel brand. The transaction resulted in a gain of $11,998 that was recorded in the line item gain from the sale of subsidiary in the Company's consolidated statement of operations. Included in the determination of the gain is goodwill of $7,205 that was allocated to the transaction in accordance with FASB authoritative guidance for subsequent measure of goodwill which requires the Company to allocate goodwill to the disposed business based on the relative fair values of the business disposed and the portion of the reporting unit that was retained.

The Company determined, in accordance with FASB authoritative guidance, that the disposal did not meet the definition of a discontinued operation as the disposal did not represent a significant disposal nor was the disposal a strategic shift in the Company's strategy.

Restricted Cash

12 Months Ended

Dec. 31, 2014

Restricted Cash.

Restricted Cash

(3) Restricted Cash

The Company classifies restricted cash as short-term and a current asset if the cash is expected to be used in operations within a year or to acquire a current asset. Otherwise, the restricted cash is classified as long-term. Restricted cash consisted of the following as of December 31, 2013 and 2014:

	December 31, 2013		December 31, 2014
Short-term restricted cash
Standby letters of credit	$	1,822	$	1,753
DCEMB revenue bonds		6,581		—
Canton bonds		—		4,259

Total short-term restricted cash	$	8,403	$	6,012

Investments

12 Months Ended

Dec. 31, 2014

Investments

Investments

(4) Investments

Available-for-sale investments are carried at fair value, inclusive of unrealized gains and losses. Net unrealized gains and losses are included in other comprehensive income (loss) net of applicable income taxes. Gains or losses on sales of available-for-sale investments are recognized on the specific identification basis. All of the Company's short-term investments are classified as available-for-sale securities.

The Company reviews available-for-sale investments for other- than-temporary declines in fair value below their cost basis each quarter, and whenever events or changes in circumstances indicate that the cost basis of an asset may not be recoverable. This evaluation is based on a number of factors, including the length of time and the extent to which the fair value has been below its cost basis and adverse conditions related specifically to the security, including any changes to the credit rating of the security. As of December 31, 2014, the Company believes its carrying values for its available-for-sale investments are properly recorded.

Short-term investments as of December 31, 2013 are summarized as follows:

	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds & notes	$	60,047	$	(252	)	$	59,795
Corporate bonds		43,166		(342	)		42,824
Certificate of deposits		35,630		(9	)		35,621

Total short-term investments	$	138,843	$	(603	)	$	138,240

Short-term investments as of December 31, 2014 are summarized as follows:

	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds & notes	$	38,668	$	(16	)	$	38,652
Zero coupon bonds		3,308		(2	)		3,306
Corporate bonds		45,274		(41	)		45,233
Certificate of deposits		35,355		—			35,355

Total short-term investments	$	122,605	$	(59	)	$	122,546

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Other Receivables

12 Months Ended

Dec. 31, 2014

Other Receivables

Other Receivables

(5) Other Receivables

Other receivables at December 31, 2013 and 2014 consisted of the following:

	2013		2014
Loans to customers to finance vehicle purchases	$	5,919	$	8,257
Accrued customer billings		6,327		10,143
Fuel tax and carbon credits		6,740		34,250
Other		7,299		3,573

	$	26,285	$	56,223

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Land, Property and Equipment

12 Months Ended

Dec. 31, 2014

Land, Property and Equipment

Land, Property and Equipment

(6) Land, Property and Equipment

Land, property and equipment at December 31, 2013 and 2014 are summarized as follows:

	2013			2014
Land	$	1,707		$	2,858
LNG liquefaction plants		93,685			94,636
RNG plants		47,932			45,359
Station equipment		194,240			265,086
LNG trailers		22,667			40,067
Other equipment		62,127			74,796
Construction in progress		204,548			163,737

		626,906			686,539
Less accumulated depreciation		(139,052	)		(172,270	)

	$	487,854		$	514,269

Included in the land, property and equipment are capitalized software costs of $18,214 and $21,004 as of December 31, 2013 and December 31, 2014, respectively. The accumulated amortization on the capitalized software costs is $7,747 and $10,740 as of December 31, 2013 and December 31, 2014, respectively. The Company recorded $1,812, $3,079, and $2,993 of amortization expense related to the capitalized software costs in 2012, 2013 and 2014, respectively.

As of December 31, 2013 and 2014, $13,930 and $11,032, respectively, are included in accounts payable balances, which amounts are related to additions of property and equipment within the respective year. These amounts are excluded from the consolidated statements of cash flows as they are non-cash investing activities.

Investment in Other Entities	12 Months Ended
Investment in Other Entities	Dec. 31, 2014
Investment in Other Entities
Investment in Other Entities	(7) Investment in Other Entities The Company previously invested in Clean Energy del Peru ("Peru JV"), a former joint venture in Peru that operated CNG stations. The Company accounted for its investment in Peru JV under the equity method of accounting as the Company had the ability to exercise significant influence over Peru JV's operations while the Company maintained an ownership interest in Peru JV. In March 2013, the Company completed the sale of its entire ownership interest in Peru JV for $6,119 after receiving a dividend distribution of $1,091, and recognized a gain of $4,705. On September 16, 2014, the Company formed a joint venture with Mansfield called Mansfield Clean Energy Partners LLC ("MCEP") , which is designed to provide natural gas fueling solutions to bulk fuel haulers in the U.S. The Company and Mansfield each have a 50% ownership interest in MCEP. The Company accounts for its interest using the equity method of accounting as the Company has the ability to exercise significant influence over MCEP's operations. The Company recorded a loss from this investment of $490 and has an investment balance of $5,510 at December 31, 2014.

Accrued Liabilities

12 Months Ended

Dec. 31, 2014

Accrued Liabilities

Accrued Liabilities

(8) Accrued Liabilities

Accrued liabilities at December 31, 2013 and 2014 consisted of the following:

	2013		2014
Salaries and wages	$	6,768	$	9,041
Accrued gas and equipment purchases		8,035		12,340
Accrued property and other taxes		5,448		5,178
Accrued professional fees		1,335		1,084
Accrued employee benefits		2,898		3,208
Accrued warranty liability		2,545		2,302
Accrued interest		4,216		3,748
Other		15,500		19,859

	$	46,745	$	56,760

Long-Term Debt

12 Months Ended

Dec. 31, 2014

Long-term Debt

Long-term Debt

(9) Long-Term Debt

DCEMB Revenue Bonds

On December 29, 2014, the Company sold its interest in DCE and its wholly owned subsidiary DCEMB. DCEMB's obligations to pay amounts due under certain tax-exempt revenue bonds issued in 2011 were included in the sale and, as a result, are not obligations of the Company as of the date of such sale. Such revenue bonds were previously included as an investing activity in the consolidated statement of cash flows, and the sale of such revenue bonds was included in the consolidated statement of operations in the line item gain from sale of subsidiary.

IMW Notes

In connection with the closing of the Company's acquisition of IMW, the Company agreed to make future payments consisting of four annual payments in the amount of $5,000 in Canadian dollars ("CAD") and $7,500 in U.S. dollars (each an "IMW Note" and collectively, the "IMW Notes") , all of which had been paid as of February 2014. Each payment under the IMW Notes consisted of CAD$5,000 in cash and $7,500 in cash and/or shares of the Company's common stock (the exact combination of cash and/or stock was determined by the Company in its discretion). In January 2011, the Company paid $5,000 in cash and $7,500 in shares of its common stock. The Company paid CAD$5,000 in cash in January 2012 and $3,750 in shares of its common stock in each of August 2012 and October 2012. The Company paid CAD$5,000 in cash and $7,500 in shares of its common stock in February 2013. In February 2014, the Company paid the final payment of CAD$5,000 in cash, $3,750 in cash and $3,750 in shares of its common stock. The IMW Notes that were settled with shares of the Company's common stock are not included in the consolidated statements of cash flows as they are non-cash financing activities.

HSBC Lines of Credit

In connection with the closing of the Company's acquisition of IMW, the Company entered into an Assumption Agreement (the "Assumption Agreement") with HSBC Bank Canada ("HSBC") pursuant to which the Company assumed the obligations and liabilities of IMW under the following arrangements with HSBC (collectively, the "IMW Lines of Credit"):

(i)	An operating line of credit with a limit of CAD $13,000 to assist in financing the day-to-day working capital needs of IMW. The interest on amounts outstanding is payable at IMW's option at (a) HSBC's Prime Rate plus 1.00% per annum, (b) HSBC's U.S. Base Rate plus 1.00% per annum, or LIBOR plus 2.25% per annum, subject to availability.
(ii)	A demand revolving line of credit with a limit of CAD$2,000 bearing interest at the same rate as that of the operating line of credit discussed above, to assist in financing IMW's import requirements.
(iii)	A demand revolving bank guarantee and standby letter of credit line with a limit of CAD$1,115.
(iv)	A bank guarantee line with a limit of CAD$3,000, which allows IMW to provide guarantees and/or standby letters of credit to overseas suppliers or bid/performance deposits on contracts.
(v)	A forward exchange contract line with a limit of CAD$13,750 that allows IMW to enter into foreign exchange forward contracts up to the notional limit of CAD$13,750.
(vi)	An operating line of credit with a limit of 5,000 Renminbi ("RMB") (CAD$945) bearing interest at the 6 month People's Bank of China rate plus 2.5% and a sub-limit bank guarantee line of 5,000 RMB. The aggregate of the balances in the lines cannot exceed 5,000 RMB.
(vii)	A 16,750 Bangladeshi Taka (CAD$245) operating line of credit bearing interest at 14%.
(viii)	A 170,000 Colombian Peso (CAD$82) operating line of credit bearing interest at the Colombia benchmark rate plus 7 to 12%.

The IMW Lines of Credit were secured by a general security agreement providing a first priority security interest in all present and after acquired personal property of IMW. On October 2, 2014, the Company paid the outstanding balance on (i) above and it, along with a (ii), (iv) and (v) above, was cancelled. The outstanding balances under the remaining arrangements described above are included in Other Debt in the long-term debt summary table below.

7.5% Notes

On July 11, 2011, the Company entered into a loan agreement (the "CHK Agreement") with Chesapeake NG Ventures Corporation ("Chesapeake"), an indirect wholly owned subsidiary of Chesapeake Energy Corporation, whereby Chesapeake agreed to purchase from the Company up to $150,000 of debt securities (the "CHK Financing") pursuant to the issuance of three convertible promissory notes, each having a principal amount of $50,000 (each a "CHK Note" and collectively the "CHK Notes" and, together with the CHK Agreement and other transaction documents, the "CHK Loan Documents"). The first CHK Note was issued on July 11, 2011 and the second CHK Note was issued on July 10, 2012.

On June 14, 2013 (the "Transfer Date"), Boone Pickens and Green Energy Investment Holdings, LLC, an affiliate of Leonard Green & Partners, L.P. (collectively, the "Buyers"), and Chesapeake entered into a note purchase agreement ("Note Purchase Agreement") pursuant to which Chesapeake sold the outstanding CHK Notes (the "Sale") to the Buyers. Chesapeake assigned to the Buyers all of its right, title and interest under the CHK Loan Documents (the "Assignment"), and each Buyer severally assumed all of the obligations of Chesapeake under the CHK Loan Documents arising after the Sale and the Assignment including, without limitation, the obligation to advance an additional $50,000 to the Company in June 2013 (the "Assumption"). The Company also entered into the Note Purchase Agreement for the purpose of consenting to the Sale, the Assignment and the Assumption.

Contemporaneously with the execution of the Note Purchase Agreement, the Company entered into a loan agreement with each Buyer (collectively, the "Amended Agreements"). The Amended Agreements have the same terms as the CHK Agreement, other than changes to reflect the change in ownership of the CHK Notes. Immediately following execution of the Amended Agreements, the Buyers delivered $50,000 to the Company in satisfaction of the funding requirement they had assumed from Chesapeake (the "June Advance"). In addition, the Company cancelled the existing CHK Notes and re-issued replacement notes, and the Company also issued notes to the Buyers in exchange for the June Advance (the re-issued replacement notes and the notes issued in exchange for the June Advance are referred to herein as the "7.5% Notes").

The 7.5% Notes have the same terms as the original CHK Notes, other than the changes to reflect their different holders. They bear interest at the rate of 7.5% per annum and are convertible at the option of the holder into shares of the Company's common stock at a conversion price of $15.80 per Share (the "7.5% Notes Conversion Price"). Upon written notice to the Company, the holders of the 7.5% Notes have the right to exchange all or a portion of the principal and accrued and unpaid interest under each such note for shares of the Company's common stock at the 7.5% Notes Conversion Price. Additionally, subject to certain restrictions, the Company can force conversion of each 7.5% Note into shares of the its common stock if, following the second anniversary of the issuance of a 7.5% Note, such shares trade at a 40% premium to the 7.5% Notes Conversion Price for at least 20 trading days in any consecutive 30 trading day period. The entire principal balance of each 7.5% Note is due and payable seven years following its issuance and the Company may repay each 7.5% Note in shares of its common stock or cash. All of the shares issuable upon exercise of the 7.5% Notes have been registered for resale by their holders pursuant to a registration statement that has been filed with and declared effective by the Securities and Exchange Commission. The Amended Agreements restrict the use of the proceeds of the 7.5% Notes to financing the development, construction and operation of LNG stations and payment of certain related expenses. The Amended Agreements also provide for customary events of default which, if any of them occurs, would permit or require the principal of, and accrued interest on, the 7.5% Notes to become, or to be declared, due and payable.

On August 27, 2013, Green Energy Investment Holdings, LLC transferred $5,000 in principal amount of the 7.5% Notes to certain third parties.

As a result of the foregoing transactions, (i) Mr. Pickens holds 7.5% Notes in the aggregate principal amount of $65,000, which 7.5% Notes are convertible into approximately 4,113,924 shares of the Company's common stock, and (ii) Green Energy Investment Holdings, LLC holds 7.5% Notes in the aggregate principal amount of $80,000, which 7.5% Notes are convertible into approximately 5,063,291 shares of the Company's common stock.

At December 31, 2014, none of the proceeds from the 7.5% Notes were included in restricted cash as the Company had used the funds primarily to build LNG fueling stations.

SLG Notes

On August 24, 2011, the Company entered into convertible note purchase agreements (each, an "SLG Agreement" and collectively the "SLG Agreements") with each of Springleaf Investments Pte. Ltd., a wholly-owned subsidiary of Temasek Holdings Pte. Ltd., Lionfish Investments Pte. Ltd., an investment vehicle managed by Seatown Holdings International Pte. Ltd., and Greenwich Asset Holding Ltd., a wholly-owned subsidiary of RRJ Capital Master Fund I, L.P. (each, a "Purchaser" and collectively, the "Purchasers"), whereby the Purchasers agreed to purchase from the Company $150,000 of 7.5% convertible notes due in August 2016 (each a "SLG Note" and collectively the "SLG Notes"). The transaction closed and the SLG Notes were issued on August 30, 2011. On March 1, 2012, Springleaf Investments Pte. LTD transferred $24,000 principal amount of the SLG Notes to Baytree Investments (Mauritius) Pte Ltd.

The SLG Notes bear interest at the rate of 7.5% per annum and are convertible at each Purchaser's option into shares of the Company's common stock at a conversion price of $15.00 per share (the "SLG Conversion Price"). Upon written notice to the Company, the holders of the SLG Notes have the right to exchange all or any portion of the principal and accrued and unpaid interest under each such note for shares of the Company's common stock at the SLG Conversion Price. Additionally, subject to certain restrictions, the Company can force conversion of each SLG Note into shares of its common stock if, following the second anniversary of the issuance of the SLG Notes, the such shares trade at a 40% premium to the SLG Conversion Price for at least 20 trading days in any consecutive 30 trading day period. The entire principal balance of each SLG Note is due and payable five years following its issuance, and the Company may repay the principal balance of each SLG Note in shares of its common stock or cash. All of the shares issuable upon exercise of the SLG Notes have been registered for resale by their holders pursuant to a registration statement that has been filed with and declared effective by the Securities and Exchange Commission. The SLG Agreements provide for customary events of default which, if any of them occurs, would permit or require the principal of, and accrued interest on, the SLG Notes to become, or to be declared, due and payable. In April 2012, $1,003 of principal and accrued interest under an SLG Note was converted by the holder thereof into 66,888 shares of the Company's common stock. In January and February 2013, $4,030 of principal and accrued interest under an SLG Note was converted by the holder thereof into 268,664 shares of the Company's common stock. Such conversions were not included in the consolidated statements of cash flows as they are a non-cash financing activity.

GE Loans

On November 7, 2012, the Company, through two wholly owned subsidiaries (the "Borrowers"), entered into a credit agreement ("Credit Agreement") with General Electric Capital Corporation ("GE"). Pursuant to the Credit Agreement, GE agreed to loan to the Borrowers up to an aggregate of $200,000 to finance the development, construction and operation of two LNG plants (individually a "Project" and together the "Projects").

On December 29, 2014, the Borrowers and GE entered into an amendment to the Credit Agreement providing, among other things, that (i) the Credit Agreement will terminate if the initial loans under the Credit Agreement (collectively, "Loans" and, with respect to each Project "Tranche A Loans" and "Tranche B Loans") for the Projects are not made prior to December 31, 2016 (rather than December 31, 2014, as the Credit Agreement originally provided), (ii) each Project must be completed by the earlier of (a) the date that is thirty months after the funding of the initial Loans with respect to such Project and (b) December 31, 2018 (rather than December 31, 2016, as the Credit Agreement originally provided) (with respect to each Project, the "Date Certain"), and (iii) prior to the funding of the Loans, the Borrowers will be required to enter into agreements with GE Oil & Gas, Inc. relating to the purchase of equipment for the Projects.

The Borrowers' ability to obtain the Loans under the Credit Agreement is subject to the satisfaction of certain conditions, including each of the (i) acquisition of title to, or leasehold interests in, the sites upon which the Projects will be constructed, (ii) receipt of all governmental approvals necessary in connection with the design, development, ownership, construction, installation, operation and maintenance of the Projects, and (iii) commitment of all utility services necessary for the construction and operation of the Projects.

The Credit Agreement further provides that (i) the then existing Loans with respect to each Project must be converted into term loans with eight year amortization schedules ("Term Loans") on or before the Date Certain with respect to such Project (the date of such conversion with respect to each Project, the "Conversion Date"), provided that if such Loans are not converted into Term Loans by the applicable Date Certain, such Loans must be repaid by the applicable Date Certain, (ii) each Term Loan will be due and payable on the eighth anniversary of the Conversion Date with respect to such Term Loan, and (iii) at any time prior to the applicable Conversion Date, the Loans may be prepaid in whole, and at any time after the applicable Conversion Date, the Loans may be prepaid in whole or in part. The Company expects the Loans to bear interest at an annual rate equal to the then- current LIBOR rate plus 7.00%, provided that for purposes of the Credit Agreement, the then-current LIBOR rate will always be at least 1.00%. The Credit Agreement includes various customary covenants, including debt service coverage ratios, a commitment fee on the unutilized loan amounts of 0.5% per annum, and also provides for customary events of default which, if such events occur, would permit or require the Loans to become or to be declared due and payable. As of December 31, 2014, the Company has not drawn any money under the Credit Agreement and was in compliance with the financial covenants. The commitment fee, which is charged to interest expense in the consolidated statements of operations, was $1,014 for the years ended December 31, 2013 and 2014.

The Loans are secured by (i) a first priority security interest in all of the Borrowers' assets, including the Projects, and (ii) a pledge of the Borrowers' outstanding ownership interests. In addition, the Company has executed a guaranty in favor of GE ("Guaranty"), pursuant to which the Company has guaranteed all of the Borrowers' obligations under the Credit Agreement, including repayment of all Loans.

The Company and GE also entered an equity contribution agreement (the "EC Agreement") pursuant to which the Company agreed to pay at least 25% of the budgeted cost of the Projects and all additional costs that exceed such expected budgeted costs, in each case, in the form of equity contributions to the Borrowers ("Equity Contributions"). The EC Agreement also requires the Company to provide, concurrent with GE's extension of the initial Loans under the Credit Agreement, letter(s) of credit in an amount equal to the Company's then-current unfunded Equity Contributions.

Concurrently with the execution of the Credit Agreement, the Company issued to GE a warrant to purchase up to five million shares of its common stock (see note 11).

Mavrix Note

On April 25, 2013, Mavrix entered into a note purchase agreement (the "NPA") with Massachusetts Mutual Life Insurance (the "Note Purchaser") and issued to the Note Purchaser a secured multi-draw promissory note (the "Note") in the maximum aggregate principal amount of $30,000. The Note matured 12 years after its issuance date and bore interest at a rate of 12.0% per annum and paid in kind interest at a rate of 2.0% per annum. The Note Purchaser funded advances of $5,000 under the Note in each of April, September and December 2013.

In connection with the Company's sale of its interests in DCE and DCEMB, on December 29, 2014, Mavrix paid $13,594 to the Note Purchaser as payment in full of all outstanding indebtedness under the NPA and the Note. Such amount includes approximately $750 as payment of an early termination fee required pursuant to the terms of the NPA and the Note. Concurrently with such payment, the NPA, the Note and all other documents related thereto were terminated in full.

5.25% Notes

In September 2013, the Company completed a private offering of 5.25% Convertible Senior Notes due 2018 (the "5.25% Notes") and entered into an indenture governing the 5.25% Notes (the "Indenture").

The net proceeds from the sale of the 5.25% Notes after the payment of certain debt issuance costs of $7,805 were $242,195. The Company has used, and intends to continue to use, the net proceeds from the sale of the 5.25% Notes to fund capital expenditures and for general corporate purposes.

The 5.25% Notes bear interest at a rate of 5.25% per annum, payable semi- annually in arrears on October 1 and April 1 of each year, beginning on April 1, 2014. The 5.25% Notes will mature on October 1, 2018, unless purchased, redeemed or converted prior to such date in accordance with their terms and the terms of the Indenture.

Holders may convert their 5.25% Notes, at their option, at any time prior to the close of business on the business day immediately preceding the maturity date of the 5.25% Notes. Upon conversion, the Company will deliver a number of shares of its common stock, per $1 principal amount of 5.25% Notes, equal to the conversion rate then in effect (together with a cash payment in lieu of any fractional shares). The initial conversion rate for the 5.25% Notes is 64.1026 shares of the Company's common stock per $1 principal amount of Notes (which is equivalent to an initial conversion price of approximately $15.60 per share of the Company's common stock). The conversion rate is subject to adjustment upon the occurrence of certain specified events as described in the Indenture.

Upon the occurrence of certain corporate events prior to the maturity date of the 5.25% Notes, the Company will, in certain circumstances, in addition to delivering the number of shares of the Company's common stock deliverable upon conversion of the 5.25% Notes based on the conversion rate then in effect (together with a cash payment in lieu of any fractional shares), pay holders that convert their 5.25% Notes a cash make-whole payment in an amount as described in the Indenture. The Company may, at its option, irrevocably elect to settle its obligation to pay any such make-whole payment in shares of its common stock instead of in cash. The amount of any make-whole payment, whether it is settled in cash or in shares of the Company's common stock upon the Company's election, will be determined based on the date on which the corporate event occurs or becomes effective and the stock price paid (or deemed to be paid) per share of the Company's common stock in the corporate event, as described in the Indenture.

The Company may not redeem the 5.25% Notes prior to October 5, 2016. On or after October 5, 2016, the Company may, at its option, redeem for cash all or any portion of the 5.25% Notes if the closing sale price of the Company's common stock for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which notice of redemption is provided, exceeds 160% of the conversion price on each applicable trading day. In the event of the Company's redemption of the 5.25% Notes, the redemption price will equal 100% of the principal amount of the 5.25% Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for in the 5.25% Notes.

If the Company undergoes a fundamental change (as defined in the Indenture) prior to the maturity date of the 5.25% Notes, subject to certain conditions as described in the Indenture, holders may require the Company to purchase, for cash, all or any portion of their 5.25% Notes at a repurchase price equal to 100% of the principal amount of the 5.25% Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change purchase date.

The Indenture contains customary events of default with customary cure periods, including, without limitation, failure to make required payments or deliveries of shares of its common stock when due under the Indenture, failure to comply with certain covenants under the Indenture, failure to pay when due or acceleration of certain other indebtedness of the Company or certain of its subsidiaries, and certain events of bankruptcy and insolvency of the Company or certain of its subsidiaries. The occurrence of an event of default under the Indenture will allow either the trustee or the holders of at least 25% in principal amount of the then-outstanding 5.25% Notes to accelerate, or upon an event of default arising from certain events of bankruptcy or insolvency of the Company, will automatically cause the acceleration of, all amounts due under the 5.25% Notes. No events of default have occurred as of December 31, 2014.

The 5.25% Notes are senior unsecured obligations of the Company and rank senior in right of payment to the Company's future indebtedness that is expressly subordinated in right of payment to the 5.25% Notes; equal in right of payment to the Company's unsecured indebtedness that is not so subordinated; effectively junior to any of the Company's secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness (including trade payables) of the Company's subsidiaries.

Canton Bonds

On March 19, 2014, Canton Renewables LLC, ("Canton") a wholly owned subsidiary of the Company, completed the issuance of Solid Waste Facility Limited Obligation Revenue Bonds (Canton Renewables, LLC—Sauk Trail Hills Project) Series 2014 in the aggregate principal amount of $12,400 (the "Bonds").

The Bonds were issued by the Michigan Strategic Fund (the "Issuer") and the proceeds of the issuance were loaned by the Issuer to Canton pursuant to a loan agreement that became effective on March 19, 2014 (the "Loan Agreement"). The Bonds are expected to be repaid from revenue generated by Canton from the sale of RNG and are secured by the revenue and assets of Canton. The Bond repayments will be amortized through July 1, 2022, the average coupon interest rate on the Bonds is 6.6%, and all but $1,000 of the principal amount of the Bonds is non-recourse to Canton's parent companies, including the Company.

Canton used the Bond proceeds primarily to (i) refinance the cost of constructing and equipping its RNG extraction and production project in Canton, Michigan and (ii) pay a portion of the costs associated with the issuance of the Bonds. The refinancing described in the prior sentence was accomplished through distributions to the Borrower's direct and indirect parent companies who provided the financing for the RNG production facility, and such companies have used such distributions to finance construction of additional RNG extraction and processing projects and for working capital purposes.

The Loan Agreement contains customary events of default, with customary cure periods, including without limitation, failure to make required payments when due under the Loan Agreement, failure to comply with certain covenants under the Loan Agreement, certain events of bankruptcy and insolvency of Canton, and the existence of an event of default under the indenture governing the Bonds that was entered between the Issuer and The Bank of New York Mellon Trust Company, N.A., as trustee. The occurrence of an event of default under the Loan Agreement will allow the Issuer or the trustee to accelerate all amounts due under the Loan Agreement. As of December 31, 2014, Canton had met its obligations under the Loan Agreement.

Other Debt

The Company has other debt due at various dates through 2020 bearing interest at rates up to 21.42% and with a weighted average interest rate of 5.72% and 6.80% as of December 31, 2013 and 2014, respectively.

Long-term debt and capital lease obligations at December 31, 2013 and 2014 consisted of the following:

	December 31, 2013			December 31, 2014
IMW Notes	$	12,121		$	—
DCEMB notes		585			—
DCEMB revenue bonds		36,500			—
7.5% Notes		150,000			150,000
SLG Notes		145,000			145,000
5.25% Notes		250,000			250,000
Note (non-recourse to the Company)		15,097			—
Bonds ($11,150 non-recourse to the Company)		—			12,150
Capital lease obligations		3,091			2,692
Other debt		8,024			10,828

Total debt and capital lease obligations		620,418			570,670
Less amounts due within one year		(23,401	)		(4,846	)

Total long-term debt and capital lease obligations	$	597,017		$	565,824

The following is a summary of aggregate maturities of long-term debt and capital lease obligations for each of the years ending December 31:

	2015		2016		2017		2018		2019		Thereafter
7.5% Notes		—		—		—		50,000		50,000		50,000
SLG Notes		—		145,000		—		—		—		—
5.25% Notes		—		—		—		250,000		—		—
Canton Bonds ($11,150 non-recourse to the Company)		1,240		1,390		1,420		1,460		1,555		5,085
Capital lease obligations		700		386		483		188		183		752
Other debt		2,906		2,009		2,147		1,916		1,313		537

Total	$	4,846	$	148,785	$	4,050	$	303,564	$	53,051	$	56,374

Derivative Transactions	12 Months Ended
Derivative Transactions	Dec. 31, 2014
Derivative Transactions
Derivative Transactions	(10) Derivative Transactions The Company had no commodity future contracts or forward exchange contracts outstanding during 2014. The Company marks -to -market its open futures positions and forward exchange contracts at the end of each period and records the net unrealized gain or loss during the period in derivative (gains) losses in the consolidated statements of operations or in accumulated other comprehensive income (loss) in the consolidated balance sheets in accordance with the applicable accounting guidance. In the years ended December 31, 2012, and 2013, the Company recorded unrealized gains of $2,151, and $108, respectively, in other comprehensive income (loss) related to its futures contracts. Of the Company's net futures contracts liability of $107 at December 31, 2012, $5 was recorded as an asset in prepaid expenses and other current assets and $112 was recorded as an accrued liability in the Company's consolidated balance sheet at December 31, 2012. The Company's ineffectiveness related to its futures contracts in the years ended December 31, 2012 and 2013 was insignificant. The Company's ineffectiveness related to its forward exchange contracts for the year ended December 31, 2013 was insignificant, and there were no forward contracts in place during 2012. During the years ended December 31, 2012 and 2013, the Company recognized a loss of $2,370 and $65, respectively, in cost of sales in the accompanying consolidated statements of operations related to its futures contracts that were settled during the respective years. These amounts were reclassified from accumulated other comprehensive income (loss).

- Definition

The entire disclosure for derivative instruments and hedging activities including, but not limited to, risk management strategies, non-hedging derivative instruments, assets, liabilities, revenue and expenses, and methodologies and assumptions used in determining the amounts.

+ References

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+ Details

Stockholders' Equity

12 Months Ended

Dec. 31, 2014

Stockholders' Equity

Stockholders' Equity

(11) Stockholders' Equity

Authorized Shares

The Company's certificate of incorporation authorizes the issuance of two classes of capital stock designated as common stock and preferred stock, each having $0.0001 par value per share. As of December 31, 2014, the Company was authorized to issue 225,000,000 shares, of which 224,000,000 shares are designated common stock and 1,000,000 shares are designated preferred stock.

Dividend Provisions

The Company did not declare nor pay any dividends during the years ended December 31, 2012, 2013 or 2014.

Voting Rights

Each holder of common stock has the right to one vote per share owned on matters presented for stockholder action.

Issuance of Common Stock and Warrants

On October 28, 2008, the Company entered into a Placement Agent Agreement (the "Placement Agent Agreement") relating to the sale and issuance by the Company to select investors of 4,419,192 units (the "Units"), with each Unit consisting of (i) one share of the Company's common stock, (ii) a warrant to purchase up to 0.75 shares of the Company's common stock (the "Series I Warrant"), and (iii) one warrant to purchase up to 0.2571 shares of the Company's common stock (the "Series II Warrant"). The price of each Unit was $7.92 per Unit. The transaction closed on November 3, 2008, and the Company issued 4,419,192 shares of common stock, Series I Warrants to purchase up to 3,314,394 shares of common stock, and Series II Warrants to purchase up to 1,136,364 shares of common stock. The Company received approximately $32,484 after deducting the placement agent's fees and other offering expenses related to the Unit sale. The proceeds of $32,484 were allocated between the common stock, the Series I Warrants and the Series II Warrants. The Company allocated $19,166, $9,745 and $3,573 to the common stock, the Series I Warrants and the Series II Warrants, respectively.

The Series I Warrants became exercisable beginning six months from the date of issuance, have a term of seven years from the date they became exercisable, and carry an exercise price of $12.68 per share. On November 10, 2010, the Company entered into an amendment with one of the holders of the Series I Warrants pursuant to which the expiration date of such warrant for the purchase of 1,183,712 shares of common stock was changed to November 10, 2010. In consideration of the modification to the expiration date, the Company agreed to pay the holder of such warrant approximately $3,172. The Company received notice on November 10, 2010 that such warrant was being exercised in full, and issued 1,183,712 shares of its common stock for an aggregate exercise price of approximately $15,009. Upon exercise, the Company recognized a gain of approximately $3,208 related to the transaction. For additional information on the Series I Warrants, see note 18.

The Series II Warrants became exercisable on November 5, 2008 upon the failure of the California Alternative Fuel Vehicles and Renewable Energy Act, or Proposition 10, in the California statewide election. The Series II Warrants were all exercised on a cashless basis at the exercise price of $0.01 per share, which resulted in the issuance of 1,134,759 shares of common stock to the Series II Warrant holders on November 12, 2008.

Concurrently with the execution of the Credit Agreement on November 7, 2012, the Company issued to GE a warrant (the "GE Warrant"), which entitles GE to purchase up to an aggregate of five million shares of the Company's common stock at a price per share of $0.01. The shares subject to the GE Warrant, as it was originally issued, were to become exercisable pursuant to the following schedule: (i) 500,000 shares were immediately exercisable (the "Commitment Fee Shares"), (ii) an additional 1,250,000 shares were to become exercisable at the time that the first Tranche A Loan is made under the Credit Agreement, (iii) an additional 1,250,000 shares were to become exercisable at the time that the first Tranche B Loan is made under the Credit Agreement, (iv) an additional 1,000,000 shares were to become exercisable at the time that Tranche A Loans in aggregate principal amount of at least $15,000 have been made under the Credit Agreement, and (v) the remaining 1,000,000 shares were to become exercisable at the time that Tranche B Loans in aggregate principal amount of at least $15,000 have been made under the Credit Agreement; provided, however, that if no Loans were made as contemplated by (ii) through (v) above pursuant to the Credit Agreement, an additional 500,000 shares (the "Termination Shares") were to become exercisable. On December 29, 2014, the Company and GE amended the GE Warrant to provide that the shares subject to the GE Warrant become exercisable pursuant to the following schedule: (i) the Commitment Fee Shares continue to be fully exercisable, (ii) the Termination Shares became exercisable on December 31, 2014, (iii) an additional 1,250,000 shares become exercisable at the time that the first Tranche A Loan is made under the Credit Agreement, (iv) an additional 1,250,000 shares become exercisable at the time that the first Tranche B Loan is made under the Credit Agreement, (v) an additional 750,000 shares become exercisable at the time that Tranche A Loans in aggregate principal amount of at least $15,000 have been made under the Credit Agreement, and (vi) the remaining 750,000 shares become exercisable at the time that Tranche B Loans in aggregate principal amount of at least $15,000 have been made under the Credit Agreement.

The GE Warrant terminates on November 7, 2022. During the exercise period, if the Company issues or sells any shares of its common stock other than exempted securities (as defined in the GE Warrant) for a price per share less than a price equal to 80% of the market price on the day of such issue or sale, then, immediately after such issuance and sale, the number of shares then purchasable shall be increased on a proportionate basis by a formula set forth in the GE Warrant. All of the shares issuable upon exercise of the GE Warrant have been registered for resale by the holder thereof pursuant to a registration statement filed with and declared effective by the Securities and Exchange Commission.

The Company measured the fair value of the 5,000,000 shares underlying the GE Warrant at $56,158 and recorded the amount in additional paid-in-capital and other long-term assets as a deferred financing cost. The fair value of the 500,000 shares that were immediately exercisable and the 500,000 shares that became exercisable on December 31, 2014 are being amortized over the estimated term of the Credit Agreement on the straight-line basis. The fair value of the remaining 4,000,000 shares will be allocated proportionately to the draws of the related Loans as they become exercisable and amortized over the estimated term of the draws using the effective interest method. The issuance of the GE Warrant is not included in the consolidated statements of cash flows as it is a non-cash financing activity.

Conversion of Convertible Debt into Common Stock

In April 2012, $1,003 of principal and accrued interest under a SLG Note was converted by the holder thereof into 66,888 shares of the Company's common stock.

In January and February 2013, $4,030 of principal and accrued interest under an SLG Note was converted by the holder thereof into 268,664 shares of the Company's common stock.

Stock-Based Compensation

The following table summarizes the compensation expense and related income tax benefit related to the stock-based compensation expense recognized during the years ended December 31, 2012, 2013 and 2014:

	Years Ended December 31,
	2012		2013		2014
Stock-based compensation expense	$	22,087	$	23,008	$	11,514

Stock-based compensation expense, net of tax	$	22,087	$	23,008	$	11,514

Stock Option Plans

In December 2002, the Company adopted its 2002 Stock Option Plan ("2002 Plan"). When the 2002 Plan was available for the issuance of new awards, the Company's board of directors determined eligibility, vesting schedules, and exercise prices for options granted thereunder. Options generally have a term of ten years.

Under the 2002 Plan, eligible persons could be issued options for services rendered to the Company. Under the 2002 Plan, the purchase price per share for each option granted could not be less than 100% of the fair market value of the Company's common stock on the date of such option grant; provided, however, that the purchase price per share of common stock issued to a 10% stockholder could not be less than 110% of the fair market value of the Company's common stock on the date of such option grant. Options generally vest over a three-year period.

In December 2006, the Company adopted its 2006 Equity Incentive Plan ("2006 Plan"). The 2006 Plan was effective on May 24, 2007, the date the Company completed its initial public offering of common stock. The 2002 Plan became unavailable for new awards upon the effectiveness of the 2006 Plan. If any outstanding option under the 2002 Plan expires or is cancelled, the shares allocable to the unexercised portion of that option will be added to the share reserve under the 2006 Plan and will be available for grant under the 2006 Plan. As of December 31, 2014, the Company had 18,890,500 shares reserved for issuance under its option plans. At December 31, 2014, the Company had 779,127 shares available for future grant under the 2006 Plan.

Stock Options

The following table summarizes stock option activity during the year ended December 31, 2014:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2013		11,526,998		$	11.79
Options granted		957,000			10.23
Options exercised		(468,279	)		3.78
Options forfeited		(529,418	)		13.40

Outstanding, December 31, 2014		11,486,301			11.91		5.04		—


Exercisable, December 31, 2014		9,875,201			11.94		4.46		—

As of December 31, 2014, there was $6,967 of total unrecognized compensation cost related to non-vested shares underlying outstanding stock options. That cost is expected to be recognized over a weighted average period of 1.5 years. The total fair value of shares vested during the year ended December 31, 2014 was $8,101.

The Company is obligated to issue new shares of its common stock upon exercise of outstanding stock options. The intrinsic value of all stock options exercised during 2012, 2013 and 2014 was $18,822, $935, and $2,568, respectively.

The fair value of each stock option granted during the year ended December 31, 2014 was estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions:

Dividend yield		0.00%
Expected volatility		52.3% to 67.0%
Risk-free interest rate		1.1% to 1.8%
Expected life in years		6.0

The weighted-average grant date fair value of options granted during the years ended December 31, 2012, 2013, and 2014, was $7.95, $6.86, and $5.32, respectively. The volatility amounts used during the periods were estimated based on the Company's historical volatility and the Company's implied volatility of its traded options. The expected lives used during the periods were based on historical exercise periods and the Company's anticipated exercise periods for its outstanding stock options. The risk free rates used during the periods were based on the U.S. Treasury yield curve for the expected life of the stock options at the time of grant. The Company recorded $14,199, $13,751, and $7,286 of stock option expense during the years ended December 31, 2012, 2013 and 2014, respectively. The Company has not recorded any tax benefit related to its stock option expense.

Market-Based Restricted Stock Units

The Company issued 2,034,500 market-based restricted stock units ("Market-Based RSUs") to certain key employees during 2012 and 2014. A holder of Market-Based RSUs will receive one share of the Company's common stock for each Market-Based RSU held if (x) between two years and four years from the date of grant of the Market-Based RSU, the closing price of the Company's common stock equals or exceeds, for twenty consecutive trading days, 135% of the closing price of the Company's common stock on the Market-Based RSU grant date (the "Stock Price Condition") and (y) the holder is employed by the Company at the time the Stock Price Condition is satisfied. If the Stock Price Condition is not satisfied prior to four years from the date of grant, the Market-Based RSUs will be automatically forfeited. The Market-Based RSUs are subject to the terms and conditions of the Company's 2006 Plan and a Notice of Grant of Restricted Stock Unit and Restricted Stock Unit Agreement.

The following table summarizes the Company's Market-Based RSU activity during the year ended December 31, 2014:

	Number of ares			Weighted Average Fair Value at Grant Date		Weighted Average Remaining Contractual Term (in years)
Outstanding, December 31, 2013		1,545,000		$	11.42
RSUs granted		489,500			8.26
RSUs vested		—
RSUs forfeited		(265,500	)		10.62

Outstanding and non-vested, December 31, 2014		1,769,000		$	10.67		1.57

As of December 31, 2014, there was $2,191 of total unrecognized compensation cost related to non-vested shares underlying outstanding Market-Based RSUs. That cost is expected to be recognized over a weighted average period of 1.1 years.

The Company recorded $8,821 and $2,556 of expense in 2013 and 2014, respectively, related to the Market-Based RSUs. The Company has not recorded any tax benefit related to its Market-Based RSU expense.

The fair value of the Market-Based RSUs granted during the year ended December 31, 2014 was estimated on the date of grant using the Monte Carlo method and using the following assumptions:

	February 2, 2014
Dividend yield		0.00	%
Expected volatility		47.0	%
Risk-free interest rate		1.1	%
Expected life in years		2.0

Service-Based Restricted Stock Units

The Company has issued service-based restricted stock units ("Service-Based RSUs") to key employees that vest annually over the three years following the date of issuance at a rate of 34%, 33% and 33%, respectively, if the holder is in service to the Company at each vesting date. The Service-Based RSUs are subject to the terms and conditions of the Company's 2006 Plan and a Notice of Grant of Restricted Stock Unit and Restricted Stock Unit Agreement.

The following table summarizes the Company's Service-Based RSU activity during the year ended December 31, 2014:

	Number of Shares			Weighted Average Fair Value at Grant Date		Weighted Average Remaining Contractual Term (in years)
Nonvested at December 31, 2013		45,836		$	13.09
RSUs granted		792,500			5.54
RSUs vested		(15,584	)		13.09
RSUs forfeited		—

Outstanding and non-vested at December 31, 2014		822,752		$	5.82		2.85

As of December 31, 2014, there was $4,186 of total unrecognized compensation cost related to non-vested shares underlying outstanding Service-Based RSUs. That cost is expected to be recognized evenly over a period of 2.8 years.

The Company recorded $51 and $365 of expense in 2013 and 2014, respectively, related to the Service-Based RSUs. The Company has not recorded any tax benefit related to its Service-Based RSU expense.

The fair value of each Service-Based RSU granted in during the year ended December 31, 2014 was estimated using the closing stock price of the Company's common stock on the date of grant.

Employee Stock Purchase Plan

On May 7, 2013, the Company adopted an employee stock purchase plan (the "ESPP"), pursuant to which eligible employees may purchase shares of the Company's common stock at 85% of the fair market value of the common stock on the last trading day of two consecutive, non-concurrent offering periods each year. The Company has reserved 2,500,000 shares of its common stock for issuance under the ESPP, and the first offering period under the ESPP commenced on September 1, 2013.

The Company recorded $29 and $67 of expense related to the ESPP during 2013 and 2014, respectively. The Company has not recorded any tax benefits related to its ESPP expense. At December 31, 2014, the Company had sold an aggregate of 57,881 shares pursuant to the ESPP.

Non-Qualified Non-Public Subsidiary Unit Options

In September 2013, the Company's wholly owned subsidiary Clean Energy Renewable Fuels, LLC ("CERF") adopted the Clean Energy Renewable Fuels, LLC 2013 Unit Option Plan (the "CERF Plan"). 150,000 Class B units representing membership interests in CERF were initially reserved for issuance under the CERF Plan.

The following table summarizes CERF's unit option activity during the year ended December 31, 2014:

	Number of Units		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2013		115,000	$	40.80
Options granted		—		—		—		—

Outstanding and non-vested, December 31, 2014		115,000	$	40.80		8.72	$	—

As of December 31, 2014, there was $2,070 of total unrecognized compensation cost related to non-vested units underlying outstanding unit options. That cost is expected to be recognized over a weighted average period of 1.8 years.

The fair value of each unit option is estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions:

Dividend yield	0.00	%
Expected volatility	96.4	%
Risk-free interest rate	1.9	%
Expected life in years	6.0

The grant date fair value of options granted in September 2013 was $31.65, which was determined contemporaneously with the grants. The volatility amounts used during the period were estimated based on the historical volatility of a certain peer group of CERF for a period commensurate with the expected life of the unit options granted. The expected life used was CERF's anticipated exercise periods for its outstanding unit options. The risk free rate was based on the U.S. Treasury yield curve for the expected life of the unit options at the time of grant. CERF recorded $356 and $1,240 of unit option expense during 2013 and 2014, respectively. CERF has not recorded any tax benefit related to its unit option expense.

Income Taxes

12 Months Ended

Dec. 31, 2014

Income Taxes

Income Taxes

(12) Income Taxes

The components of loss before income taxes for the years ended December 31, 2012, 2013, and 2014 are as follows:

	2012			2013			2014
U.S.	$	(91,608	)	$	(40,195	)	$	(64,913	)
Foreign		(7,960	)		(23,009	)		(24,871	)

	$	(99,568	)	$	(63,204	)	$	(89,784	)

The provision (benefit) for income taxes consists of the following:

	2012			2013		2014
Current:
Federal	$	269		$	87	$	190
State		302			310		238
Foreign		(61	)		2,910		1,017

Total current		510			3,307		1,445
Deferred:
Federal		—			134		29
State		—			47		(10	)
Foreign		784			227		(389	)

Total deferred		784			408		(370	)

Total	$	1,294		$	3,715	$	1,075

Income tax expense (benefit) for the years ended December 31, 2012, 2013 and 2014 differs from the "expected" amount computed using the federal income tax rate of 35% as a result of the following:

	2012			2013			2014
Computed expected tax expense (benefit)	$	(34,849	)	$	(22,121	)	$	(30,415	)
Nondeductible expenses		5,194			7,216			10,690
Tax rate differential on foreign earnings		(717	)		2,993			5,733
Basis difference on sale		—			(6,457	)		—
Tax credits		—			(35,604	)		(8,286	)
Other		(1,442	)		82			(1,121	)
Change in valuation allowance		33,108			57,606			24,474

Total tax expense (benefit)	$	1,294		$	3,715		$	1,075

During the fourth quarter of 2014, federal tax legislation extended the VETC through December 31, 2014 with retroactive effect to the beginning of 2014. In addition, during the first quarter of 2013, federal tax legislation extended the VETC through December 31, 2013 with retroactive effect to the beginning of 2012. Federal tax guidance was issued in 2013 that clarified that the VETC in excess of the Company's fuel tax obligation, which is collected from customers, can be excluded from taxable income. The Company recorded a federal tax benefit of $8,221 and $7,068 related to the exclusion of VETC associated with 2014 and 2013 fuel sales in excess of its fuel tax obligation and a federal tax benefit of $27,497 was recorded in 2013 related to the exclusion of similar VETC amounts associated with fuel sales from 2006 through 2012. These amounts increased the Company's deferred tax asset attributed to its federal net operating loss carryforwards and the Company's deferred tax asset valuation allowance.

Deferred tax assets and liabilities result from differences between the financial statement carrying amounts and the tax bases of existing assets and liabilities. The tax effect of temporary differences that give rise to deferred tax assets and liabilities as of December 31, 2013 and 2014 are as follows:

	2013			2014
Deferred tax assets:
Accrued expenses	$	3,367		$	4,834
Sales-type leases		997			908
Alternative minimum tax and general business credits		4,903			4,966
Derivative loss		1,161			527
Stock option expense		20,832			21,741
Other		4,693			2,596
Loss carryforwards		126,563			147,706

Total deferred tax assets		162,516			183,278
Less valuation allowance		(136,969	)		(160,436	)

Net deferred tax assets		25,547			22,842

Deferred tax liabilities:
Depreciation and amortization		(21,800	)		(20,028	)
Goodwill		(1,626	)		(3,864	)
Partnership income		(3,540	)		—

Total deferred tax liabilities		(26,966	)		(23,892	)

Net deferred tax liabilities	$	(1,419	)	$	(1,050	)

At December 31, 2014, the Company had federal, state and foreign net operating loss carryforwards of approximately $369,332, $284,828 and $50,334, respectively. The Company's federal, state and foreign net operating loss carryforwards will, if not utilized, expire beginning in 2026, 2015 and 2028, respectively. The Company also has federal tax credit carryforwards of $4,750 that will expire beginning in 2026. Due to the change of ownership provisions of Internal Revenue Code Section 382, utilization of a portion of the Company's net operating loss and tax credit carryforwards may be limited in future periods.

In assessing the realizability of the net deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers projected future taxable income and tax planning strategies in making this assessment. As of December 31, 2013 and 2014, the Company provided a valuation allowance of $136,969, and $160,436, respectively, to reduce the net deferred tax assets due to uncertainty surrounding the realizability of these assets. The net increase in the valuation allowance for the years ended December 31, 2013, and 2014 was $55,711, and $23,468, respectfully. The changes in the valuation allowance were primarily attributable to operating losses incurred in certain jurisdictions for which a full valuation allowance was established.

As of December 31, 2014, the Company has not provided deferred U.S. income taxes or foreign withholding taxes on temporary differences of approximately $3,327 resulting from earnings of certain non-U.S. subsidiaries which are permanently reinvested outside the U.S. Unrecognized deferred taxes on remittance of these funds are not expected to be material.

The Company does not recognize the impact of a tax position in its financial statements unless the position is more likely than not to be sustained, based on the technical merits of the position. The unrecognized tax benefits of $21,974 at December 31, 2014 included $692 of tax benefits that, if recognized, would reduce the Company's annual effective tax rate. The remaining $21,282, if recognized, would not result in a tax benefit since it would be fully offset with a valuation allowance.

The following is a tabular reconciliation of the total amounts of unrecognized tax benefits for the years ended December 31, 2012, 2013 and 2014:

Unrecognized tax benefit—December 31, 2012	$	515
Gross increases—tax positions in current year		16,685
Gross increases—tax positions in prior years		198

Unrecognized tax benefit—December 31, 2013		17,398
Gross increases—tax positions in current year		4,722
Gross increases—tax positions in prior years		(146	)

Unrecognized tax benefit—December 31, 2014	$	21,974

The increase in the Company's unrecognized tax benefits during 2013 and 2014 is primarily attributable to the portion of VETC offset by the fuel tax the Company collected from its customers as an unrecognized tax benefit during 2013 and 2014. The Company believes the portion of VETC that is offset by the fuel tax the Company collects from its customers can be excluded from taxable income, although the ultimate outcome of this tax position is uncertain. The Company's changes in its unrecognized tax benefits related to prior years were attributable to transfer pricing on the sale of goods and services.

FASB authoritative guidance requires the Company to accrue interest and penalties where there is an underpayment of taxes based on the Company's best estimate of the amount ultimately to be paid. The Company's policy is to recognize interest accrued related to unrecognized tax benefits and penalties as income tax expense. During each of the years ended December 31, 2012, 2013 and 2014, the Company accrued interest of $21, $75, and, $120, respectively.

The Company is subject to taxation in the United States and various states and foreign jurisdictions. The Company's tax years for 2010 through 2014 are subject to examination by various tax authorities. The Company is no longer subject to U.S. examination for years before 2011, and state examinations for years before 2010.

A number of years may elapse before an uncertain tax position is finally resolved. It is often difficult to predict the final outcome or the timing of resolution of any particular uncertain tax position, but the Company believes that its reserves for income taxes reflect the most probable outcomes. The Company adjusts the reserve, as well as the related interest and penalties, in light of changing facts and circumstances. The amount of penalties accrued is immaterial. Settlement of any particular position would usually require the use of cash and result in the reduction of the related reserve, or there could be a change in the amount of the Company's net operating loss. The resolution of a matter would be recognized as an adjustment to the provision for income taxes at the effective tax rate in the period of resolution. The Company does not expect a significant increase or decrease in its uncertain tax positions within the next twelve months.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2014

Commitments and Contingencies

Commitments and Contingencies

(13) Commitments and Contingencies

Environmental Matters

The Company is subject to federal, state, local, and foreign environmental laws and regulations. The Company does not anticipate any expenditures to comply with such laws and regulations which would have a material impact on the Company's consolidated financial position, results of operations, or liquidity. The Company believes that its operations comply, in all material respects, with applicable federal, state, local and foreign environmental laws and regulations.

Litigation, Claims and Contingencies

The Company may become party to various legal actions that arise in the ordinary course of its business. During the course of its operations, the Company is also subject to audit by tax authorities for varying periods in various federal, state, local and foreign tax jurisdictions. Disputes may arise during the course of such audits as to facts and matters of law. It is impossible to determine the ultimate liabilities that the Company may incur resulting from any such lawsuits, claims and proceedings, audits, commitments, contingencies and related matters or the timing of these liabilities, if any. If these matters were to ultimately be resolved unfavorably, an outcome not currently anticipated, it is possible that such outcome could have a material adverse effect upon the Company's consolidated financial position, results of operations, or liquidity. However, the Company believes that the ultimate resolution of such matters will not have a material adverse effect on the Company's consolidated financial position, results of operations, or liquidity.

Operating Lease Commitments

The Company leases facilities, including the land for its LNG production plant in Boron, California, and certain equipment under noncancelable operating leases expiring at various dates through 2038. The following schedule represents the future minimum lease obligations for all noncancelable operating leases as of December 31, 2014:

Fiscal year:
2015	$	10,343
2016		9,124
2017		7,492
2018		5,348
2019		5,153
Thereafter		21,958

Total future minimum lease payments	$	59,418

Rent expense, including variable rent, totaled $7,737, $10,504, and $10,140 for the years ended December 31, 2012, 2013 and 2014, respectively.

Long-Term Take-or-Pay Natural Gas Supply Contracts

In October 2007, the Company entered into an LNG supply contract with Desert Gas Services (formerly known as Spectrum Energy Services, LLC) ("DGS") to purchase, on a take-or-pay basis over a term of ten years, 45,000 gallons per day, which was increased to 65,000 gallons per day in March 2014, of LNG from a plant constructed by DGS in Ehrenberg, Arizona, which is near the California border. This obligation began in March 2010, and for the years ended December 31, 2012, 2013 and 2014, the Company paid approximately $8,153, $11,404, and $14,267 respectively, under the take-or-pay supply contract. The contract expires in October 2017. At December 31, 2014, the fixed commitments under this contract totaled approximately $7,974, $4,628, and 3,857 for the years ending December 31, 2015 through December 31, 2017.

Geographic Information

12 Months Ended

Dec. 31, 2014

Geographic Information

Geographic Information

(14) Geographic Information

Several of the Company's functions, including marketing, engineering, and finance are performed at the corporate level. As a result, significant interdependence and overlap exists among the Company's geographic areas. Accordingly, revenue, operating income (loss), and long-lived assets shown for each geographic area may not be the amounts which would have been reported if the geographic areas were independent of one another. Revenue by geographic area is based on where services are rendered and finished goods are sold. Operation income (loss) is based on the location of the entity selling the finished goods or providing the services.

	2012			2013			2014
Revenue:
United States	$	286,125		$	292,250		$	360,881
Canada		8,364			13,922			16,241
Other		39,519			46,303			51,818

Total revenue	$	334,008		$	352,475		$	428,940


Operating income (loss):
United States	$	(69,030	)	$	(44,797	)	$	(41,543	)
Canada		(188	)		(1,594	)		(3,087	)
Other		(1,304	)		(5,300	)		(9,734	)

Total operating income (loss)	$	(70,522	)	$	(51,691	)	$	(54,364	)


Long-lived assets:
United States	$	480,067		$	544,638		$	582,028
Canada		122,291			103,997			85,984
Other		3,547			7,537			6,854

Total long-lived assets	$	605,905		$	656,172		$	674,866

The Company's goodwill and intangible assets at December 31, 2012, 2013 and 2014 relate to its United States operations and its BAF (through June 28, 2013, see note 2), IMW, Northstar, and NG Advantage (beginning on October 14, 2014, see note 2) operations.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
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+ Details

401(k) Plan	12 Months Ended
401(k) Plan	Dec. 31, 2014
401(k) Plan
401(k) Plan	(15) 401(k) Plan The Company has established a savings plan ("Savings Plan") which is qualified under Section 401(k) of the Internal Revenue Code. Eligible employees may elect to make contributions to the Savings Plan through salary deferrals of up to 90% of their base pay, subject to Internal Revenue Code limitations. The Company may make discretionary contributions to the Savings Plans that are subject to limitations. For the years ended December 31, 2012, 2013, and 2014 the Company contributed approximately $1,289, $1,448, and $1,040 of matching contributions to the Savings Plan, respectively.

Supplier Concentrations	12 Months Ended
Supplier Concentrations	Dec. 31, 2014
Supplier Concentrations
Supplier Concentrations	(16) Supplier Concentrations During 2012, 2013, and 2014, the Company incurred approximately 8%, 3%, and 4% respectively, of its natural gas expense related to its LNG sales from Williams Gas Processing Company pursuant to a floating rate purchase contract that includes minimum purchase commitments. During 2012, 2013, and 2014, the Company incurred approximately 31%, 22%, and 17% respectively, of its natural gas expense related to its LNG sales from Shell Energy, which supplies the Company's LNG plant in California (through April of 2013) and DGS's plant in Arizona, where the Company has a take or pay obligation. During 2012, 2013 and 2014, the Company incurred approximately 16%, 7%, and 3%, respectively, of its natural gas costs related to its CNG operations from the SoCal Gas Company (through May of 2013) and San Diego Gas and Electric. During the second quarter of 2013, the Company switched from Shell Energy and SoCal Gas Company to BP Energy for its natural gas supply to its LNG plant in California and to its CNG operations in California. The Company incurred approximately 24% of its natural gas expense related to its LNG and CNG sales from BP Energy during 2014. Any inability to obtain natural gas in the amounts needed on a timely basis or at commercially reasonable prices could result in interruption of gas deliveries or increases in gas costs, which could have a material adverse effect on the Company's business, financial condition, and results of operations until alternative sources could be identified and established at a reasonable cost.

Capitalized Lease Obligation and Receivables

12 Months Ended

Dec. 31, 2014

Capitalized Lease Obligation and Receivables

Capitalized Lease Obligation and Receivables

(17) Capitalized Lease Obligation and Receivables

The Company leases equipment under capital leases with a weighted-average interest rate of 15.02%. At December 31, 2014, future payments under these capital leases are as follows:

2015	$	1,006
2016		644
2017		686
2018		365
2019		357
Thereafter		938

Total minimum lease payments		3,996
Less amount representing interest		(1,304	)

Present value of future minimum lease payments		2,692
Less current portion		(700	)

Capital lease obligations, less current portion	$	1,992

The value of the equipment under capital lease as of December 31, 2013 and 2014 was $6,802 and $4,898, with related accumulated amortization of $4,185 and $1,936, respectively.

The Company also leases certain fueling station equipment to certain customers under sales-type leases at a weighted average effective interest rate of 4.37%. The leases are payable in varying monthly installments through February 2018.

At December 31, 2014, future receipts under these leases are as follows:

2015	$	487
2016		395
2017		194
2018		65
2019		—
Thereafter		—

Total		1,141
Less amount representing interest		(70	)

	$	1,071

Fair Value Measurements

12 Months Ended

Dec. 31, 2014

Fair Value Measurements

Fair Value Measurements

(18) Fair Value Measurements

The Company follows the authoritative guidance for fair value measurements with respect to assets and liabilities that are measured at fair value on a recurring basis and nonrecurring basis. Under the standard, fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as of the measurement date. The standard also establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs market participants would use in valuing the asset or liability developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company's assumptions about the factors market participants would use in valuing the asset or liability developed based upon the best information available in the circumstances. The hierarchy consists of the following three levels: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs (other than quoted prices) that are observable for the asset or liability, either directly or indirectly; Level 3 inputs are unobservable inputs for the asset or liability. Categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

During the twelve months ended December 31, 2014, the Company's financial instruments consisted of available-for-sale securities, debt instruments, a contingent consideration obligation, and its Series I warrants. For available-for-sale securities, the fair value is determined by the most recent trading prices available for each security or for comparable securities, and thus represent Level 2 fair value measurements. The Company uses projected financial results for the respective entity, discounted to reflect the time value of money, to value its contingent consideration obligations, which is considered to be a Level 3 fair value measurement. The fair values of the Company's debt instruments approximated their carrying values at December 31, 2013 and 2014. The Company uses the Black-Scholes model to value the Series I Warrants. The Company believes the best method to approximate a market participant's view of the volatility of its Series I Warrants has been to use the implied volatilities of its short-term (i.e. 3 to 9 month) traded options and extrapolate the data over the remaining term of the Series I Warrants, which was approximately 1.33 years as of December 31, 2014. This method has been utilized consistently in the periods presented. Given that the extrapolation beyond the term of the short term exchange traded options is not based on observable market inputs for a significant portion of the remaining term of the warrants, the Series I Warrants have been classified as a Level 3 fair value measurement.

The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2013 and December 31, 2014, respectively:

Description	Balance at December 31, 2013		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities(1):
Certificate of deposits	$	35,621	$	—	$	35,621	$	—
Municipal bonds and notes		59,795		—		59,795		—
Corporate bonds		42,824		—		42,824		—
Liabilities:
Contingent consideration obligation		384		—		—		384
Series I Warrants(2)		7,164		—		—		7,164

Description	Balance at December 31, 2014		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities(1):
Certificate of deposits	$	35,355	$	—	$	35,355	$	—
Municipal bonds and notes		38,652		—		38,652		—
Zero coupon bonds		3,306		—		3,306		—
Corporate bonds		45,233		—		45,233		—
Liabilities:
Contingent consideration obligation		—		—		—		—
Series I Warrants(2)		1,416		—		—		1,416

(1)	Included in short-term investments in the consolidated balance sheets. See note 4 for further information.
(2)	Included in other long-term liabilities in the consolidated balance sheets.

The following tables provide a reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis in the tables above that used significant unobservable inputs (Level 3).

Liabilities: Contingent Consideration	2013			2014
Beginning Balance	$	1,516		$	384
Gain included in earnings		(1,132	)		(208	)
Payments		—			(176	)
Transfers In/Out		—			—

Ending Balance	$	384			—

Liabilities: Series I Warrants	2013			2014
Beginning Balance	$	8,102		$	7,164
Gain included in earnings		(938	)		(5,748	)
Issuance of warrants		—			—
Exercise of warrants		—			—
Transfers In/Out		—			—

Ending Balance	$	7,164		$	1,416

There were no long-lived asset impairments in 2013. In the fourth quarter of 2014, the Company determined that a long-lived intangible asset related to a contract acquired in the IMW acquisition was impaired due to the cancellation of the contract. Accordingly, the Company recorded an impairment charge of $4,772 related to intangible assets.

Valuation processes for Level 3 fair value measurements and sensitivity to changes in significant unobservable inputs

Fair value measurements of liabilities which fall within Level 3 of the fair value hierarchy are determined by the Company's accounting department, who report to the Company's Chief Financial Officer. The fair value measurements are compared to those of the prior reporting periods to ensure that changes are consistent with expectations of management based upon the sensitivity and nature of the inputs.

Series I Warrant Liability

The Company estimated the fair value of its Series I Warrant liability using the Black-Scholes model based on the following inputs as of December 31, 2014:

Unobservable Input		Range or Weighted Average
Current market price of the Company's common stock		$ 5.00
Exercise price of the warrant		$ 12.68
Dividend yield		0.00%
Remaining term of the warrant		1.33
Implied volatility of the Company's common stock		85.0% - 85.9%
Assumed discount rate		Simple average of 0.46%

Significant changes in any of those inputs in isolation can result in a significant change in the fair value measurement. Generally, a positive change in the market price of the Company's common stock, an increase in the volatility of the Company's common stock, or an increase in the remaining term of the warrant would result in a directionally similar change in the estimated fair value of the Company's Series I Warrants and thus an increase in the associated liability. An increase in the assumed discount rate or a decrease in the positive differential between the warrant's exercise price and the market price of the Company's common stock would result in a decrease in the estimated fair value measurement of the Series I Warrants and thus a decrease in the associated liability. The Company has not, nor does it plan to, declare dividends on its common stock, and thus, there is no directionally similar change in the estimated fair value of the warrants due to the dividend assumption.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2014
Subsequent Event
Subsequent Events	(19) Subsequent Events None.

Schedule II: Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2014

Schedule II: Valuation and Qualifying Accounts

Schedule II: Valuation and Qualifying Accounts

	Allowances for Doubtful Trade Receivables			Allowance for Doubtful Notes Receivables
Balance at December 31, 2011	$	712		$	20
Charges (benefit) to operations		435			924
Deductions		(242	)		(35	)

Balance at December 31, 2012		905			909
Charges (benefit) to operations		454			1,507
Deductions		(527	)		—

Balance at December 31, 2013		832			2,416
Charges (benefit) to operations		387			890
Deductions		(467	)		(456	)

Balance at December 31, 2014	$	752		$	2,850

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2014

Summary of Significant Accounting Policies

Basis of Presentation

Use of Estimates

Cash and Cash Equivalents

The Company considers all highly liquid investments with maturities of three months or less on the date of acquisition to be cash equivalents.

Fair Value of Financial Instruments

Inventories

Inventories consisted of the following as of December 31, 2013 and 2014:

	2013		2014
Raw materials and spare parts	$	30,521	$	31,389
Work in process		3,011		3,292
Finished goods		290		15

Total	$	33,822	$	34,696

Property and Equipment

Long-Lived Assets

Goodwill and Intangible Assets

The Company's intangible assets as of December 31, 2013 and 2014 were as follows:

	2013			2014
Technology	$	54,400		$	54,400
Lease agreements		21,045			—
Customer relationships		12,791			16,430
Acquired contracts		13,121			3,694
Trademark and trade names		6,700			8,200
Non-compete agreements		2,126			2,060

Total intangible assets		110,183			84,784
Less accumulated amortization		(30,003	)		(24,384	)
Foreign currency rate change		(410	)		(5,039	)

Net intangible assets	$	79,770		$	55,361

Included above is a trademark of indefinite useful life with a carrying value of $1,200 as of December 31, 2013 and 2014.

Warranty Liability

	December 31, 2013			December 31, 2014
Warranty liability at beginning of year	$	2,665		$	2,545
Costs accrued for new warranty contracts and changes in estimates for pre-existing warranties		3,551			3,746
Service obligations honored		(3,089	)		(3,989	)
Sale of subsidiary		(582	)		—

Warranty liability at end of year	$	2,545		$	2,302

Asset Retirement Obligations

	2013			2014
Beginning balance	$	1,313		$	1,461
Liabilities incurred		89			118
Liabilities settled		(5	)		—
Accretion expense		64			59

Ending balance	$	1,461		$	1,638

Revenue Recognition

Alternative Fuels Excise Tax Credit

LNG Transportation Costs

The Company records the costs incurred to transport LNG to its customers in the line item cost of sales in the accompanying statements of operations.

Advertising Costs

Advertising costs are expensed as incurred. Advertising costs amounted to $1,340, $1,391, and $439 for the years ended December 31, 2012, 2013, 2014 respectively.

Stock-Based Compensation

Foreign Currency Translation

Income Taxes

Net Loss Per Share

The following potentially dilutive securities have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive:

	2012		2013		2014
Stock options		12,083,677		11,526,998		11,486,301
Warrants		2,130,682		2,130,682		6,130,682
Convertibles notes		16,262,226		35,185,979		35,185,979
Restricted stock units		1,545,000		1,590,836		2,591,752

Comprehensive Income (Loss)

Concentration of Credit Risk

Recently Adopted Accounting Changes and Recently Issued and Adopted Accounting Standards

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2014

Summary of Significant Accounting Policies

Schedule of inventories

	2013		2014
Raw materials and spare parts	$	30,521	$	31,389
Work in process		3,011		3,292
Finished goods		290		15

Total	$	33,822	$	34,696

Schedule of the Company's intangible assets

	2013			2014
Technology	$	54,400		$	54,400
Lease agreements		21,045			—
Customer relationships		12,791			16,430
Acquired contracts		13,121			3,694
Trademark and trade names		6,700			8,200
Non-compete agreements		2,126			2,060

Total intangible assets		110,183			84,784
Less accumulated amortization		(30,003	)		(24,384	)
Foreign currency rate change		(410	)		(5,039	)

Net intangible assets	$	79,770		$	55,361

Schedule of changes in the warranty liability

	December 31, 2013			December 31, 2014
Warranty liability at beginning of year	$	2,665		$	2,545
Costs accrued for new warranty contracts and changes in estimates for pre-existing warranties		3,551			3,746
Service obligations honored		(3,089	)		(3,989	)
Sale of subsidiary		(582	)		—

Warranty liability at end of year	$	2,545		$	2,302

Summary of activity of the asset retirement obligation

	2013			2014
Beginning balance	$	1,313		$	1,461
Liabilities incurred		89			118
Liabilities settled		(5	)		—
Accretion expense		64			59

Ending balance	$	1,461		$	1,638

Schedule of potentially dilutive securities that have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive

	2012		2013		2014
Stock options		12,083,677		11,526,998		11,486,301
Warrants		2,130,682		2,130,682		6,130,682
Convertibles notes		16,262,226		35,185,979		35,185,979
Restricted stock units		1,545,000		1,590,836		2,591,752

Acquisitions and Divestitures (Tables)

12 Months Ended

Dec. 31, 2014

MGES

Acquisitions and Divestitures

Summary of allocation of the aggregate purchase price to the estimated fair value of the assets acquired and liabilities assumed as of the acquisition date

Current assets	$	4,475
Property, plant and equipment		1,369
Identifiable intangible assets		600
Goodwill		16,555

Total assets acquired		22,999
Current liabilities assumed		(1,984	)

Total purchase price	$	21,015

NG Advantage

Acquisitions and Divestitures

Summary of allocation of the aggregate purchase price to the estimated fair value of the assets acquired and liabilities assumed as of the acquisition date

Current assets	$	40,558
Property, plant and equipment		20,862
Other long-term assets		5,115
Identifiable intangible assets		5,600
Goodwill		21,070

Total assets acquired		93,205
Current liabilities assumed		(9,165	)

Long-term debt including capital leases assumed, excluding current installments		(17,604	)
Other liabilities		(711	)

Non-controlling interest		(28,075	)

Total purchase price	$	37,650

Restricted Cash (Tables)

12 Months Ended

Dec. 31, 2014

Restricted Cash.

Schedule of components of restricted cash

	December 31, 2013		December 31, 2014
Short-term restricted cash
Standby letters of credit	$	1,822	$	1,753
DCEMB revenue bonds		6,581		—
Canton bonds		—		4,259

Total short-term restricted cash	$	8,403	$	6,012

Investments (Tables)

12 Months Ended

Dec. 31, 2014

Investments

Summary of Short-term investments

Short-term investments as of December 31, 2013 are summarized as follows:

	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds & notes	$	60,047	$	(252	)	$	59,795
Corporate bonds		43,166		(342	)		42,824
Certificate of deposits		35,630		(9	)		35,621

Total short-term investments	$	138,843	$	(603	)	$	138,240

Short-term investments as of December 31, 2014 are summarized as follows:

	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds & notes	$	38,668	$	(16	)	$	38,652
Zero coupon bonds		3,308		(2	)		3,306
Corporate bonds		45,274		(41	)		45,233
Certificate of deposits		35,355		—			35,355

Total short-term investments	$	122,605	$	(59	)	$	122,546

Other Receivables (Tables)

12 Months Ended

Dec. 31, 2014

Other Receivables

Schedule of other receivables

	2013		2014
Loans to customers to finance vehicle purchases	$	5,919	$	8,257
Accrued customer billings		6,327		10,143
Fuel tax and carbon credits		6,740		34,250
Other		7,299		3,573

	$	26,285	$	56,223

Land, Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2014

Land, Property and Equipment

Summary of land, property and equipment

	2013			2014
Land	$	1,707		$	2,858
LNG liquefaction plants		93,685			94,636
RNG plants		47,932			45,359
Station equipment		194,240			265,086
LNG trailers		22,667			40,067
Other equipment		62,127			74,796
Construction in progress		204,548			163,737

		626,906			686,539
Less accumulated depreciation		(139,052	)		(172,270	)

	$	487,854		$	514,269

Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2014

Accrued Liabilities

Schedule of accrued liabilities

	2013		2014
Salaries and wages	$	6,768	$	9,041
Accrued gas and equipment purchases		8,035		12,340
Accrued property and other taxes		5,448		5,178
Accrued professional fees		1,335		1,084
Accrued employee benefits		2,898		3,208
Accrued warranty liability		2,545		2,302
Accrued interest		4,216		3,748
Other		15,500		19,859

	$	46,745	$	56,760

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2014

Long-term Debt

Schedule of long-term debt

	December 31, 2013			December 31, 2014
IMW Notes	$	12,121		$	—
DCEMB notes		585			—
DCEMB revenue bonds		36,500			—
7.5% Notes		150,000			150,000
SLG Notes		145,000			145,000
5.25% Notes		250,000			250,000
Note (non-recourse to the Company)		15,097			—
Bonds ($11,150 non-recourse to the Company)		—			12,150
Capital lease obligations		3,091			2,692
Other debt		8,024			10,828

Total debt and capital lease obligations		620,418			570,670
Less amounts due within one year		(23,401	)		(4,846	)

Total long-term debt and capital lease obligations	$	597,017		$	565,824

Summary of aggregate maturities of long term debt and capital lease obligations

	2015		2016		2017		2018		2019		Thereafter
7.5% Notes		—		—		—		50,000		50,000		50,000
SLG Notes		—		145,000		—		—		—		—
5.25% Notes		—		—		—		250,000		—		—
Canton Bonds ($11,150 non-recourse to the Company)		1,240		1,390		1,420		1,460		1,555		5,085
Capital lease obligations		700		386		483		188		183		752
Other debt		2,906		2,009		2,147		1,916		1,313		537

Total	$	4,846	$	148,785	$	4,050	$	303,564	$	53,051	$	56,374

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2014

Stock-based compensation

Summary of compensation expense and related income tax benefit related to the stock-based compensation expense recognized

	Years Ended December 31,
	2012		2013		2014
Stock-based compensation expense	$	22,087	$	23,008	$	11,514

Stock-based compensation expense, net of tax	$	22,087	$	23,008	$	11,514

Stock Options | 2006 Plan

Stock-based compensation

Summary of stock option activity

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2013		11,526,998		$	11.79
Options granted		957,000			10.23
Options exercised		(468,279	)		3.78
Options forfeited		(529,418	)		13.40

Outstanding, December 31, 2014		11,486,301			11.91		5.04		—


Exercisable, December 31, 2014		9,875,201			11.94		4.46		—

Schedule of assumptions used to estimate the fair value of each award using the Black-Scholes option pricing model

Dividend yield		0.00%
Expected volatility		52.3% to 67.0%
Risk-free interest rate		1.1% to 1.8%
Expected life in years		6.0

Stock Options | CERF Plan

Stock-based compensation

Summary of stock option activity

	Number of Units		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2013		115,000	$	40.80
Options granted		—		—		—		—

Outstanding and non-vested, December 31, 2014		115,000	$	40.80		8.72	$	—

Schedule of assumptions used to estimate the fair value of each award using the Black-Scholes option pricing model

Dividend yield	0.00	%
Expected volatility	96.4	%
Risk-free interest rate	1.9	%
Expected life in years	6.0

Market-Based RSUs

Stock-based compensation

Summary of the Company's RSU activity

	Number of ares			Weighted Average Fair Value at Grant Date		Weighted Average Remaining Contractual Term (in years)
Outstanding, December 31, 2013		1,545,000		$	11.42
RSUs granted		489,500			8.26
RSUs vested		—
RSUs forfeited		(265,500	)		10.62

Outstanding and non-vested, December 31, 2014		1,769,000		$	10.67		1.57

Schedule of assumptions used in estimating fair value of each RSU on the date of grant

	February 2, 2014
Dividend yield		0.00	%
Expected volatility		47.0	%
Risk-free interest rate		1.1	%
Expected life in years		2.0

Service-Based RSUs

Stock-based compensation

Summary of the Company's RSU activity

	Number of Shares			Weighted Average Fair Value at Grant Date		Weighted Average Remaining Contractual Term (in years)
Nonvested at December 31, 2013		45,836		$	13.09
RSUs granted		792,500			5.54
RSUs vested		(15,584	)		13.09
RSUs forfeited		—

Outstanding and non-vested at December 31, 2014		822,752		$	5.82		2.85

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2014

Income Taxes

Schedule of components of loss before income taxes

	2012			2013			2014
U.S.	$	(91,608	)	$	(40,195	)	$	(64,913	)
Foreign		(7,960	)		(23,009	)		(24,871	)

	$	(99,568	)	$	(63,204	)	$	(89,784	)

Schedule of provision (benefit) for income taxes

	2012			2013		2014
Current:
Federal	$	269		$	87	$	190
State		302			310		238
Foreign		(61	)		2,910		1,017

Total current		510			3,307		1,445
Deferred:
Federal		—			134		29
State		—			47		(10	)
Foreign		784			227		(389	)

Total deferred		784			408		(370	)

Total	$	1,294		$	3,715	$	1,075

Schedule of reconciliation of federal income tax rate to the actual effective tax rate

	2012			2013			2014
Computed expected tax expense (benefit)	$	(34,849	)	$	(22,121	)	$	(30,415	)
Nondeductible expenses		5,194			7,216			10,690
Tax rate differential on foreign earnings		(717	)		2,993			5,733
Basis difference on sale		—			(6,457	)		—
Tax credits		—			(35,604	)		(8,286	)
Other		(1,442	)		82			(1,121	)
Change in valuation allowance		33,108			57,606			24,474

Total tax expense (benefit)	$	1,294		$	3,715		$	1,075

Schedule of tax effect of temporary differences that give rise to deferred tax assets and liabilities

	2013			2014
Deferred tax assets:
Accrued expenses	$	3,367		$	4,834
Sales-type leases		997			908
Alternative minimum tax and general business credits		4,903			4,966
Derivative loss		1,161			527
Stock option expense		20,832			21,741
Other		4,693			2,596
Loss carryforwards		126,563			147,706

Total deferred tax assets		162,516			183,278
Less valuation allowance		(136,969	)		(160,436	)

Net deferred tax assets		25,547			22,842

Deferred tax liabilities:
Depreciation and amortization		(21,800	)		(20,028	)
Goodwill		(1,626	)		(3,864	)
Partnership income		(3,540	)		—

Total deferred tax liabilities		(26,966	)		(23,892	)

Net deferred tax liabilities	$	(1,419	)	$	(1,050	)

Schedule of reconciliation of the total amounts of unrecognized tax benefits

Unrecognized tax benefit—December 31, 2012	$	515
Gross increases—tax positions in current year		16,685
Gross increases—tax positions in prior years		198

Unrecognized tax benefit—December 31, 2013		17,398
Gross increases—tax positions in current year		4,722
Gross increases—tax positions in prior years		(146	)

Unrecognized tax benefit—December 31, 2014	$	21,974

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2014

Commitments and Contingencies

Schedule of future minimum lease obligations for all noncancelable operating leases

Fiscal year:
2015	$	10,343
2016		9,124
2017		7,492
2018		5,348
2019		5,153
Thereafter		21,958

Total future minimum lease payments	$	59,418

Geographic Information (Tables)

12 Months Ended

Dec. 31, 2014

Geographic Information

Schedule of revenue, operating income (loss), and long-lived assets shown for each geographic area

	2012			2013			2014
Revenue:
United States	$	286,125		$	292,250		$	360,881
Canada		8,364			13,922			16,241
Other		39,519			46,303			51,818

Total revenue	$	334,008		$	352,475		$	428,940


Operating income (loss):
United States	$	(69,030	)	$	(44,797	)	$	(41,543	)
Canada		(188	)		(1,594	)		(3,087	)
Other		(1,304	)		(5,300	)		(9,734	)

Total operating income (loss)	$	(70,522	)	$	(51,691	)	$	(54,364	)


Long-lived assets:
United States	$	480,067		$	544,638		$	582,028
Canada		122,291			103,997			85,984
Other		3,547			7,537			6,854

Total long-lived assets	$	605,905		$	656,172		$	674,866

Capitalized Lease Obligation and Receivables (Tables)

12 Months Ended

Dec. 31, 2014

Capitalized Lease Obligation and Receivables

Schedule of future payments under the capital leases

2015	$	1,006
2016		644
2017		686
2018		365
2019		357
Thereafter		938

Total minimum lease payments		3,996
Less amount representing interest		(1,304	)

Present value of future minimum lease payments		2,692
Less current portion		(700	)

Capital lease obligations, less current portion	$	1,992

Schedule of future receipts under the leases

2015	$	487
2016		395
2017		194
2018		65
2019		—
Thereafter		—

Total		1,141
Less amount representing interest		(70	)

	$	1,071

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Measurements

Schedule of information by level for assets and liabilities that are measured at fair value on a recurring basis

Description	Balance at December 31, 2013		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities(1):
Certificate of deposits	$	35,621	$	—	$	35,621	$	—
Municipal bonds and notes		59,795		—		59,795		—
Corporate bonds		42,824		—		42,824		—
Liabilities:
Contingent consideration obligation		384		—		—		384
Series I Warrants(2)		7,164		—		—		7,164

Description	Balance at December 31, 2014		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities(1):
Certificate of deposits	$	35,355	$	—	$	35,355	$	—
Municipal bonds and notes		38,652		—		38,652		—
Zero coupon bonds		3,306		—		3,306		—
Corporate bonds		45,233		—		45,233		—
Liabilities:
Contingent consideration obligation		—		—		—		—
Series I Warrants(2)		1,416		—		—		1,416

(1)	Included in short-term investments in the consolidated balance sheets. See note 4 for further information.
(2)	Included in other long-term liabilities in the consolidated balance sheets.

Reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis that used significant unobservable inputs (Level 3)

Liabilities: Contingent Consideration	2013			2014
Beginning Balance	$	1,516		$	384
Gain included in earnings		(1,132	)		(208	)
Payments		—			(176	)
Transfers In/Out		—			—

Ending Balance	$	384			—

Liabilities: Series I Warrants	2013			2014
Beginning Balance	$	8,102		$	7,164
Gain included in earnings		(938	)		(5,748	)
Issuance of warrants		—			—
Exercise of warrants		—			—
Transfers In/Out		—			—

Ending Balance	$	7,164		$	1,416

Level 3 | Series I Warrant Liabilities

Valuation processes for Level 3 Fair Value Measurements

Schedule of fair value measurements of liabilities which fall within level 3 of the fair value hierarchy

Unobservable Input		Range or Weighted Average
Current market price of the Company's common stock		$ 5.00
Exercise price of the warrant		$ 12.68
Dividend yield		0.00%
Remaining term of the warrant		1.33
Implied volatility of the Company's common stock		85.0% - 85.9%
Assumed discount rate		Simple average of 0.46%

Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2014 USD ($) item	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Inventories
Raw materials and spare parts	$ 31,389	$ 30,521
Work in process	3,292	3,011
Finished goods	15	290
Total	34,696	33,822
Property and Equipment
Proceeds from grants	$ 959	$ 3,114	$ 5,908
Minimum
Property and Equipment
Number of natural gas fueling locations \| item	540
LNG liquefaction plants
Property and Equipment
Estimated useful lives	20 years
Station equipment
Property and Equipment
Estimated useful lives	10 years
LNG trailers
Property and Equipment
Estimated useful lives	10 years
Other equipment \| Minimum
Property and Equipment
Estimated useful lives	3 years
Other equipment \| Maximum
Property and Equipment
Estimated useful lives	7 years

Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Thousands						3 Months Ended	12 Months Ended
	Dec. 29, 2014	Oct. 14, 2014	Jun. 28, 2013	May 06, 2013	May 06, 2013	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and intangible assets
Impairment charges for goodwill or indefinite lived intangible asset							$ 0	$ 0	$ 0
Foreign currency translation gains (losses) included in goodwill balances							(3,687)	(3,098)
Total intangible assets						$ 84,784	84,784	110,183
Less accumulated amortization						(24,384)	(24,384)	(30,003)
Foreign currency rate change							(5,039)	(410)
Net intangible assets						55,361	55,361	79,770
Carrying value of trademark of indefinite useful life						1,200	1,200	1,200
Amortization expense							7,024	9,016	$ 10,875
Estimated amortization expense
2015						5,130	5,130
2016						5,130	5,130
2017						4,916	4,916
2018						4,366	4,366
2019						3,465	3,465
Thereafter						32,354	32,354
Long-lived intangible impairment							4,772
MGES
Goodwill and intangible assets
Increase in goodwill on acquisition				$ 16,555
Identifiable intangible assets				$ 600	$ 600
MGES \| Minimum
Goodwill and intangible assets
Estimated useful lives					1 year
MGES \| Maximum
Goodwill and intangible assets
Estimated useful lives					6 years
NG Advantage
Goodwill and intangible assets
Increase in goodwill on acquisition		$ 21,070
Identifiable intangible assets		$ 5,600
NG Advantage \| Minimum
Goodwill and intangible assets
Estimated useful lives		4 years
NG Advantage \| Maximum
Goodwill and intangible assets
Estimated useful lives		7 years
IMW
Estimated amortization expense
Long-lived intangible impairment						4,772
BAF
Goodwill and intangible assets
Reduction in goodwill on sale			$ 774
Dallas Clean Energy, LLC
Goodwill and intangible assets
Reduction in goodwill on sale	$ 7,205
Technology
Goodwill and intangible assets
Total intangible assets						54,400	$ 54,400	54,400
Technology \| Minimum
Goodwill and intangible assets
Estimated useful lives							2 years
Technology \| Maximum
Goodwill and intangible assets
Estimated useful lives							20 years
Lease agreements
Goodwill and intangible assets
Total intangible assets								21,045
Lease agreements \| Minimum
Goodwill and intangible assets
Estimated useful lives							1 year
Lease agreements \| Maximum
Goodwill and intangible assets
Estimated useful lives							16 years
Customer relationships
Goodwill and intangible assets
Total intangible assets						16,430	$ 16,430	12,791
Customer relationships \| Minimum
Goodwill and intangible assets
Estimated useful lives							1 year
Customer relationships \| Maximum
Goodwill and intangible assets
Estimated useful lives							8 years
Acquired contracts
Goodwill and intangible assets
Total intangible assets						3,694	$ 3,694	13,121
Acquired contracts \| Minimum
Goodwill and intangible assets
Estimated useful lives							1 year
Acquired contracts \| Maximum
Goodwill and intangible assets
Estimated useful lives							10 years
Trademarks and trade names
Goodwill and intangible assets
Total intangible assets						8,200	$ 8,200	6,700
Trademarks and trade names \| Minimum
Goodwill and intangible assets
Estimated useful lives							2 years
Trademarks and trade names \| Maximum
Goodwill and intangible assets
Estimated useful lives							20 years
Non-compete agreements
Goodwill and intangible assets
Estimated useful lives							3 years
Total intangible assets						$ 2,060	$ 2,060	$ 2,126
Customer relationships and tradenames \| NG Advantage
Goodwill and intangible assets
Identifiable intangible assets		$ 5,600

Summary of Significant Accounting Policies (Details 3) $ in Thousands	12 Months Ended			63 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 $ / gal
Changes in the warrant liability
Warranty liability at beginning of year	$ 2,545	$ 2,665
Costs accrued for new warranty contracts and changes in estimates for pre-existing warranties	3,746	3,551
Service obligations honored	(3,989)	(3,089)
Sale of subsidiary		(582)
Warranty liability at end of year	2,302	2,545	$ 2,665
Asset Retirement Obligations
Asset retirement obligation, included in other long-term liabilities	1,603	1,322
Activity of the asset retirement obligation
Beginning balance	1,461	1,313
Liabilities incurred	118	89
Liabilities settled		(5)
Accretion expense	59	64
Ending balance	1,638	1,461	1,313
Alternative Fuels Excise Tax Credit
Federal fuel tax credit - CNG (in dollars per gasoline gallon equivalent) \| $ / gal				0.50
Federal fuel tax credit - LNG (in dollars per liquid gallon) \| $ / gal				0.50
VETC credits recognized as revenue	28,359	45,439
VETC credits related to prior periods		20,800
Advertising Costs
Advertising expense	439	1,391	1,340
Foreign Currency Translation
Foreign exchange transactions gains (losses)	$ (3,188)	$ (1,196)	$ 678

Summary of Significant Accounting Policies (Details 4) - shares			4 Months Ended	12 Months Ended
	Dec. 31, 2014	Nov. 07, 2012	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
GE Credit Agreement \| GE Warrant
Net Loss Per Share
Number of shares exercisable in the period	500,000	500,000				500,000
Common stock \| GE Credit Agreement \| GE Warrant
Net Loss Per Share
Anti-dilutive securities (in shares)			4,000,000
Shares issuable upon exercise included in earnings per share calculations	1,000,000
Stock Options
Net Loss Per Share
Anti-dilutive securities (in shares)				11,486,301	11,526,998	12,083,677
Series I Warrant Liabilities
Net Loss Per Share
Common stock related to the GE Warrant included in the basic and dilutive net loss per share calculation					5,000,000
Anti-dilutive securities (in shares)				6,130,682	2,130,682	2,130,682
Convertible Notes
Net Loss Per Share
Anti-dilutive securities (in shares)				35,185,979	35,185,979	16,262,226
Restricted Stock Units
Net Loss Per Share
Anti-dilutive securities (in shares)				2,591,752	1,590,836	1,545,000

Summary of Significant Accounting Policies (Details 5) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Concentration of Credit Risk
Amount in excess of FDIC insurance limits	$ 88,740	$ 237,004
IMW
Concentration of Credit Risk
Maximum percentage of foreign trade receivables covered by accounts receivable insurance	90.00%

Summary of Significant Accounting Policies (Details 6)	Dec. 29, 2014
Dallas Clean Energy, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of ownership sold	51.00%

Acquisitions and Divestitures (Details 2) $ in Thousands			1 Months Ended
Acquisitions and Divestitures (Details 2) $ in Thousands	Jun. 28, 2013 USD ($) item shares	Jun. 28, 2013 USD ($) item shares gal	Aug. 31, 2014 USD ($)	Jul. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jul. 31, 2013 USD ($) shares	Jun. 30, 2014 shares
BAF \| ServoTech
Divestitures
Ownership interest in ServoTech (as a percent)	100.00%	100.00%
BAF \| Westport Parties \| Stock purchase agreement
Divestitures
Number of common stock shares to be received \| shares	816,460	816,460
Number of common stock shares received \| shares	718,485	718,485					94,914,000
Number of common stock Holdback Shares \| shares	97,975	97,975
Period of holdback for shares to be received		1 year
Number of Holdback Shares remaining unissued \| shares							3,061,000
Number of common stock shares sold \| shares						718,485
Net proceeds from sale of common stock				$ 1,727		$ 23,722
Repayment of certain intercompany indebtedness of BAF Technologies, Inc. and ServoTech Engineering Inc. (BAF) to the Company			$ 2,478
Value of common stock shares to be received	$ 27,221	$ 27,221
Initial/adjusted gain recognized	15,498	15,498		13,993	$ 14,115
Write down in value of the Holdback Shares				$ 122	$ 1,383
BAF \| Westport Affiliates \| Marketing Agreement
Divestitures
Cash payable to entity under the agreement	$ 5,000	$ 5,000
Term of agreement	2 years
Complimentary gasoline provided under the agreement (in gallons) \| gal		750,000
Minimum number of members to be appointed by Company to operating committee \| item	1	1

Acquisitions and Divestitures (Details 3) - USD ($) $ in Thousands			1 Months Ended
	May 06, 2013	May 06, 2013	Aug. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Allocation of aggregate purchase price
Goodwill				$ 98,726	$ 88,548
MGES
Allocation of aggregate purchase price
Current assets	$ 4,475	$ 4,475
Property, plant and equipment	1,369	1,369
Identifiable intangible assets	600	600
Goodwill	16,555	16,555
Total assets acquired	22,999	22,999
Current liabilities assumed	(1,984)	(1,984)
Total purchase price	21,015	$ 21,015
MGES \| Minimum
Allocation of aggregate purchase price
Identifiable intangible assets, estimated useful lives		1 year
MGES \| Maximum
Allocation of aggregate purchase price
Identifiable intangible assets, estimated useful lives		6 years
MGES \| Stock purchase agreement
Acquisitions
Total purchase consideration	$ 20,000		$ 563
Percentage of purchase consideration payable in cash	50.00%	50.00%
Percentage of purchase consideration paid in shares	50.00%	50.00%
Cash payment	$ 9,000
Number of common stock shares issued	761,545
Amount retained	$ 1,000	$ 1,000

Acquisitions and Divestitures (Details 4) $ in Thousands	Oct. 14, 2014 USD ($) item	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Allocation of aggregate purchase price
Goodwill		$ 98,726	$ 88,548
NG Advantage
Allocation of aggregate purchase price
Current assets	$ 40,558
Property, plant and equipment	20,862
Other long-term assets	5,115
Identifiable intangible assets	5,600
Goodwill	21,070
Total assets acquired	93,205
Current liabilities assumed	(9,165)
Long-term debt including capital leases assumed, excluding current installments	(17,604)
Other liabilities	(711)
Non-controlling interest	(28,075)
Total purchase price	37,650
Assumed debt related to purchases of capital assets and working capital needs	20,439
Debt payment	$ 10,361
NG Advantage \| Minimum
Allocation of aggregate purchase price
Identifiable intangible assets, estimated useful lives	4 years
NG Advantage \| Maximum
Allocation of aggregate purchase price
Identifiable intangible assets, estimated useful lives	7 years
NG Advantage \| Customer relationships and tradenames
Allocation of aggregate purchase price
Identifiable intangible assets	$ 5,600
NG Advantage \| Common unit purchase agreement
Acquisitions and Divestitures
Total consideration	$ 37,650
Ownership interest acquired (as a percent)	53.30%
Consideration paid in cash	$ 19,000
Consideration liability	$ 18,650
Number of installments \| item	2
NG Advantage \| Due by January 2015 \| Common unit purchase agreement
Acquisitions and Divestitures
Consideration liability	$ 3,000
NG Advantage \| Due by April 2015 \| Common unit purchase agreement
Acquisitions and Divestitures
Consideration liability	$ 15,650

Acquisitions and Divestitures (Details 5) - USD ($) $ in Thousands			1 Months Ended		12 Months Ended
	Dec. 29, 2014	Sep. 04, 2014	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Sep. 03, 2012
Divestitures
Gain from sale of subsidiary					$ 11,998	$ 14,115
Goodwill			$ 98,726		$ 98,726	$ 88,548
Dallas Clean Energy, LLC
Divestitures
Percentage of ownership sold	51.00%
Dallas Clean Energy, LLC \| Cambrian
Divestitures
Ownership interest (as a percent)	49.00%
Dallas Clean Energy, LLC \| Cambrian
Divestitures
Cash consideration received on sale of subsidiary			$ 40,588	$ 6,992
Dallas Clean Energy, LLC \| Cambrian \| Mavrix
Divestitures
Percentage of ownership sold	51.00%	19.00%
Ownership interest (as a percent)							70.00%
Additional consideration that may be received prior to August 1, 2015	$ 3,000
Gain from sale of subsidiary	11,998
Goodwill	$ 7,205

Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Restricted Cash
Short-term restricted cash	$ 6,012	$ 8,403
DCEMB revenue bonds
Restricted Cash
Short-term restricted cash		6,581
Canton Bonds
Restricted Cash
Short-term restricted cash	4,259
Standby letters of credit
Restricted Cash
Short-term restricted cash	$ 1,753	$ 1,822

Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Short-term investments
Amortized Cost	$ 122,605	$ 138,843
Gross Unrealized Losses	(59)	(603)
Estimated Fair Value	122,546	138,240
Municipal bonds and notes
Short-term investments
Amortized Cost	38,668	60,047
Gross Unrealized Losses	(16)	(252)
Estimated Fair Value	38,652	59,795
Zero coupon bonds
Short-term investments
Amortized Cost	3,308
Gross Unrealized Losses	(2)
Estimated Fair Value	3,306
Corporate bonds
Short-term investments
Amortized Cost	45,274	43,166
Gross Unrealized Losses	(41)	(342)
Estimated Fair Value	45,233	42,824
Certificates of deposit
Short-term investments
Amortized Cost	35,355	35,630
Gross Unrealized Losses		(9)
Estimated Fair Value	$ 35,355	$ 35,621

Other Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Other Receivables
Other receivables	$ 56,223	$ 26,285
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	8,257	5,919
Accrued customer billings
Other Receivables
Other receivables	10,143	6,327
Fuel tax and carbon credits
Other Receivables
Other receivables	34,250	6,740
Other
Other Receivables
Other receivables	$ 3,573	$ 7,299

Land, Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Land, Property and Equipment
Land, property and equipment, gross	$ 686,539	$ 626,906
Less: accumulated depreciation	(172,270)	(139,052)
Land, property and equipment, net	514,269	487,854
Capitalized software costs, net	21,004	18,214
Accumulated amortization on the capitalized software costs	10,740	7,747
Amortization expense related to the capitalized software costs	2,993	3,079	$ 1,812
Amount included in accounts payable balances	11,032	13,930
Land
Land, Property and Equipment
Land, property and equipment, gross	2,858	1,707
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,636	93,685
RNG plants
Land, Property and Equipment
Land, property and equipment, gross	45,359	47,932
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	265,086	194,240
LNG trailers
Land, Property and Equipment
Land, property and equipment, gross	40,067	22,667
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	74,796	62,127
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 163,737	$ 204,548

Investment in Other Entities (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity method investments
Dividend distribution			$ 1,091
Gain on sale recognized			4,705
Loss from investment		$ (490)	$ (76)	$ 331
Peru JV
Equity method investments
Ownership interest sold	$ 6,119
Dividend distribution	1,091
Gain on sale recognized	$ 4,705
Mansfield Energy Corp
Equity method investments
Ownership interest (as a percent)		50.00%
Loss from investment		$ 490
Investment balance		$ 5,510

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accrued Liabilities
Salaries and wages	$ 9,041	$ 6,768
Accrued gas and equipment purchases	12,340	8,035
Accrued property and other taxes	5,178	5,448
Accrued professional fees	1,084	1,335
Accrued employee benefits	3,208	2,898
Accrued warranty liability	2,302	2,545	$ 2,665
Accrued interest	3,748	4,216
Other	19,859	15,500
Total	$ 56,760	$ 46,745

Long-Term Debt (Details) - Purchase Notes - IMW $ in Thousands, $ in Thousands			1 Months Ended
	Sep. 07, 2010 CAD ($) item	Sep. 07, 2010 USD ($) item	Feb. 28, 2014 CAD ($)	Feb. 28, 2014 USD ($)	Feb. 28, 2013 CAD ($)	Feb. 28, 2013 USD ($)	Oct. 31, 2012 USD ($)	Aug. 31, 2012 USD ($)	Jan. 31, 2012 CAD ($)	Jan. 31, 2011 USD ($)
Long-term debt
Number of annual payments \| item	4	4
Annual cash required to be paid on debt instrument	$ 5,000
Cash and/or common stock required to be paid or issued on debt instrument		$ 7,500
Amount paid			$ 5,000	$ 3,750	$ 5,000				$ 5,000	$ 5,000
Common stock issued on debt instrument				$ 3,750		$ 7,500	$ 3,750	$ 3,750		$ 7,500

Long-Term Debt (Details 2) ৳ in Thousands, ¥ in Thousands, $ in Thousands, $ in Thousands	Sep. 07, 2010 CNY (¥)	Sep. 07, 2010 COP ($)	Sep. 07, 2010 BDT (৳)	Sep. 07, 2010 CAD ($)
IMW assumed operating line of credit
Long-term debt
Line of credit limit				$ 13,000
IMW assumed operating line of credit \| HSBC's prime rate
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	1.00%
IMW assumed operating line of credit \| HSBC's US base rate
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	1.00%
IMW assumed operating line of credit \| LIBOR
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	2.25%
Demand revolving line of credit
Long-term debt
Line of credit limit				2,000
Demand revolving bank guarantee and standby letter of credit line
Long-term debt
Line of credit limit				1,115
IMW bank guarantee line
Long-term debt
Line of credit limit				3,000
IMW forward exchange contract line
Long-term debt
Line of credit limit				13,750
IMW Renminbi operating line of credit
Long-term debt
Line of credit limit	¥ 5,000			945
IMW Renminbi operating line of credit \| People's Bank of China 6 month rate
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	2.50%
IMW Renminbi sub-limit line of credit
Long-term debt
Line of credit limit \| ¥	¥ 5,000
IMW Renminbi line of credit
Long-term debt
Line of credit limit \| ¥	¥ 5,000
IMW Bangladeshi Taka operating line of credit
Long-term debt
Line of credit limit			৳ 16,750	$ 245
Interest rate (as a percent)	14.00%	14.00%	14.00%	14.00%
IMW Colombian Peso operating line of credit
Long-term debt
Line of credit limit		$ 170,000		$ 82
IMW Colombian Peso operating line of credit \| Colombia benchmark rate \| Minimum
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	7.00%
IMW Colombian Peso operating line of credit \| Colombia benchmark rate \| Maximum
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	12.00%

Long-Term Debt (Details 3) - 7.5% Notes $ / shares in Units, $ in Thousands	Aug. 27, 2013 USD ($) item	Jun. 14, 2013 USD ($) item $ / shares	Jul. 11, 2011 USD ($) item	Dec. 31, 2014 USD ($)
Long-term debt
Number of convertible promissory notes to be issued \| item			3
Principal amount of each debt instrument to be issued			$ 50,000
Interest rate (as a percent)			7.50%
Maximum
Long-term debt
Financing commitment received			$ 150,000
Boone Pickens
Long-term debt
Aggregate principal amount	$ 65,000
Boone Pickens \| Common stock
Long-term debt
Number of shares of common stock into which Notes are convertible \| item	4,113,924
Buyers
Long-term debt
Additional amount of advances under the obligation assumed		$ 50,000
Amount of advance funded		$ 50,000
Conversion price of shares (in dollars per share) \| $ / shares		$ 15.80
Percentage of the trade price of common stock that the conversion price must be at premium for the Company to force conversion		40.00%
Number of days within 30 consecutive trading days in which the trade price of the entity's common stock must be at premium of the conversion price for the Company to force conversion \| item		20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion		30 days
Period during which the debt instrument principal balance is required to be paid following its issuance		7 years
Long term restricted cash related to debt instrument				$ 0
Green Energy Investment Holdings, LLC
Long-term debt
Principal amount transferred	$ 5,000
Aggregate principal amount	$ 80,000
Green Energy Investment Holdings, LLC \| Common stock
Long-term debt
Number of shares of common stock into which Notes are convertible \| item	5,063,291

Long-Term Debt (Details 4) - SLG Notes $ / shares in Units, $ in Thousands		1 Months Ended	2 Months Ended
	Aug. 24, 2011 USD ($) item $ / shares	Apr. 30, 2012 USD ($) shares	Feb. 28, 2013 USD ($) shares	Mar. 01, 2012 USD ($)
Long-term debt
Financing commitment received	$ 150,000
Interest rate (as a percent)	7.50%
Conversion price of shares (in dollars per share) \| $ / shares	$ 15.00
Percentage of the trade price of common stock that the conversion price must be at premium for the Company to force conversion	40.00%
Number of days within 30 consecutive trading days in which the trade price of the entity's common stock must be at premium of the conversion price for the Company to force conversion \| item	20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion	30 days
Period during which the debt instrument principal balance is required to be paid following its issuance	5 years
Common stock
Long-term debt
Amount of principal and accrued interest under debt conversion		$ 1,003	$ 4,030
Common stock issued upon conversion of debt (in shares) \| shares		66,888	268,664
Baytree Investments (Mauritius) Pte Ltd
Long-term debt
Principal amount transferred				$ 24,000

Long-Term Debt (Details 5) - GE Credit Agreement $ in Thousands		24 Months Ended
	Nov. 07, 2012 USD ($) item shares	Dec. 31, 2014 USD ($)
Long-term debt
Number of wholly owned subsidiaries through which the entity entered into a financing arrangement \| item	2
Line of credit limit \| $	$ 200,000
Number of LNG production facilities being financed \| item	2
Commitment fee on the unutilized loan amounts (as a percent)	0.50%
Commitment fee \| $		$ 1,014
GE Warrant \| Common stock
Long-term debt
Number of shares that can be purchased upon exercise of warrants \| shares	5,000,000
Minimum
Long-term debt
Percentage of the budgeted costs of the Projects which the Company agreed to pay	25.00%
Maximum
Long-term debt
Amortization period following conversion into term loan	8 years
LIBOR
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	7.00%
Reference rate minimum (as a percent)	1.00%

Long-Term Debt (Details 6) - USD ($) $ in Thousands			12 Months Ended
Long-Term Debt (Details 6) - USD ($) $ in Thousands	Dec. 29, 2014	Apr. 25, 2013	Dec. 31, 2014	Dec. 31, 2013
Long-term debt
Payment of early termination fee			$ 896	$ 9,130
Mavrix Note \| Mavrix
Long-term debt
Financing commitment received		$ 30,000
Period during which the debt instrument principal balance is required to be paid following its issuance		12 years
Interest rate (as a percent)		12.00%
Paid in kind interest (as a percent)		2.00%
Amount of advance funded		$ 5,000
Amount paid	$ 13,594
Payment of early termination fee	$ 750

Long-Term Debt (Details 7) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2013 USD ($) item $ / shares shares	Sep. 30, 2010 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Long-term debt
Payment of certain debt issuance costs			$ 896	$ 9,130
5.25% Notes
Long-term debt
Interest rate (as a percent)	5.25%
Payment of certain debt issuance costs	$ 7,805
Amount of advance funded	$ 242,195
Denominator in calculation of shares per principal amount in debt conversion		$ 1
Common stock issued upon conversion of debt (in shares) \| shares	64.1026
Conversion price of shares (in dollars per share) \| $ / shares	$ 15.60
Number of days within 30 consecutive trading days in which the trade price of the entity's common stock must be at premium of the conversion price for the Company to force conversion \| item	20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion	30 days
Percentage of the trade price of common stock that the conversion price must be at premium for the Company to force conversion	160.00%
Redemption price as percentage of principal amount of notes to be redeemed	100.00%
Percentage of principal amount at which notes may be required to be repurchased in event of fundamental change by the entity	100.00%
5.25% Notes \| Minimum
Long-term debt
Percentage of principal amount of notes outstanding allowing holders to accelerate all amounts due under notes in event of default under the Indenture	25.00%

Long-Term Debt (Details 8) - Canton Bonds - USD ($) $ in Thousands	Dec. 31, 2014	Mar. 19, 2014
Long-term debt
Principal amount with recourse to the Company	$ 1,000
Canton Renewables
Long-term debt
Debt issuance amount		$ 12,400
Coupon interest rate (as a percent)		6.60%

Long-Term Debt (Details 9) - USD ($) $ in Thousands	24 Months Ended
Long-Term Debt (Details 9) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Long-term debt
Maximum interest rate on other debt borrowings	21.42%
Weighted average interest rate	6.80%	5.72%
Total debt and capital lease obligations	$ 570,670	$ 620,418
Less amounts due within one year	(4,846)	(23,401)
Total long-term debt and capital lease obligations	565,824	597,017
Summary of aggregate maturities of long-term debt
2015	4,846
2016	148,785
2017	4,050
2018	303,564
2019	53,051
Thereafter	56,374
Purchase Notes \| IMW
Long-term debt
Total debt and capital lease obligations		12,121
DCEMB notes
Long-term debt
Total debt and capital lease obligations		585
DCEMB revenue bonds
Long-term debt
Total debt and capital lease obligations		36,500
7.5% Notes
Long-term debt
Total debt and capital lease obligations	150,000	150,000
Summary of aggregate maturities of long-term debt
2018	50,000
2019	50,000
Thereafter	50,000
SLG Notes
Long-term debt
Total debt and capital lease obligations	145,000	145,000
Summary of aggregate maturities of long-term debt
2016	145,000
5.25% Notes
Long-term debt
Total debt and capital lease obligations	250,000	250,000
Summary of aggregate maturities of long-term debt
2018	250,000
Mavrix Note
Long-term debt
Total debt and capital lease obligations		15,097
Canton Bonds
Long-term debt
Total debt and capital lease obligations	12,150
Summary of aggregate maturities of long-term debt
2015	1,240
2016	1,390
2017	1,420
2018	1,460
2019	1,555
Thereafter	5,085
Capital lease obligations
Long-term debt
Total debt and capital lease obligations	2,692	3,091
Summary of aggregate maturities of long-term debt
2015	700
2016	386
2017	483
2018	188
2019	183
Thereafter	752
Other debt
Long-term debt
Total debt and capital lease obligations	10,828	$ 8,024
Summary of aggregate maturities of long-term debt
2015	2,906
2016	2,009
2017	2,147
2018	1,916
2019	1,313
Thereafter	$ 537

Derivative Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
Derivative Transactions (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Transactions
Unrealized gains on derivative instruments recognized in other comprehensive income loss		$ 108	$ 2,151
Derivative loss	$ (5,748)	(938)	(3,391)
Natural gas futures contracts
Derivative Transactions
Unrealized gains on derivative instruments recognized in other comprehensive income loss		108	2,151
Derivative liability			107
Derivative loss		$ 65	2,370
Natural gas futures contracts \| Prepaid expenses and other current assets
Derivative Transactions
Derivative asset			5
Natural gas futures contracts \| Accrued liabilities.
Derivative Transactions
Derivative liability			112
Forward exchange contracts
Derivative Transactions
Derivative liability	$ 0		$ 0

Stockholders' Equity (Details)	Dec. 31, 2014 item $ / shares shares	Dec. 31, 2013 $ / shares shares
Stockholders' Equity
Authorized number of classes of capital stock \| item	2
Common stock, Par value (in dollars per share) \| $ / shares	$ 0.0001	$ 0.0001
Preferred stock, par value (in dollars per share) \| $ / shares	$ 0.0001	$ 0.0001
Authorized shares	225,000,000
Common stock, Authorized shares	224,000,000	149,000,000
Preferred stock, Authorized shares	1,000,000	1,000,000
Number of votes per share held by holders of common stock \| item	1

Stockholder's Equity (Details 2) $ / shares in Units, $ in Thousands						1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2014 $ / shares shares	Nov. 07, 2012 USD ($) $ / shares shares	Nov. 10, 2010 USD ($) item shares	Nov. 12, 2008 $ / shares shares	Nov. 03, 2008 USD ($) $ / shares shares	Apr. 30, 2012 USD ($) shares	Feb. 28, 2013 USD ($) shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2012 USD ($) shares	Dec. 31, 2013 $ / shares	Oct. 28, 2008 $ / shares shares
Stockholders' equity
Number of units authorized under the Placement Agent Agreement											4,419,192,000
Unit price (in dollars per unit) \| $ / shares											$ 7.92
Proceeds after deducting the placement agent's fees and other offering expenses related to the sale of units \| $					$ 32,484
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001							$ 0.0001		$ 0.0001
Fair value of warrants issued, additional paid-in capital \| $									$ 56,158
SLG Notes
Stockholders' equity
Value of debt converted into shares \| $						$ 1,003	$ 4,030
Common stock issued upon conversion of debt (in shares)						66,888	268,664
Series I Warrants
Stockholders' equity
Number of shares that can be purchased upon exercise of warrants					3,314,394
Proceeds after deducting the placement agent's fees and other offering expenses related to the sale of units \| $					$ 9,745
Period from which warrants are exercisable					6 months
Expiration term					7 years
Exercise price of the warrant (in dollars per share) \| $ / shares					$ 12.68
Series II Warrant
Stockholders' equity
Number of shares that can be purchased upon exercise of warrants					1,136,364
Proceeds after deducting the placement agent's fees and other offering expenses related to the sale of units \| $					$ 3,573
Exercise price of the warrant (in dollars per share) \| $ / shares				$ 0.01
Total number of warrants exercised (in shares)				1,134,759
Amended Series I Warrant
Stockholders' equity
Number of shares that can be purchased upon exercise of warrants			1,183,712
Number of holders of warrants entering into amendment with the company \| item			1
Amount paid to holders on modification of term \| $			$ 3,172
Total number of warrants exercised (in shares)			1,183,712
Total value of warrants exercised \| $			$ 15,009
Gain on exercise of warrants \| $			$ 3,208
GE Warrant \| GE Credit Agreement
Stockholders' equity
Number of shares exercisable in the period	500,000	500,000							500,000
Additional number of shares that will be exercisable if no loans are made		500,000
Percentage of market price below which stock sale is a "Dilutive Issuance"		80.00%
Fair value of warrants issued, additional paid-in capital \| $		$ 56,158
Remaining shares to be allocated to draws as they become exercisable	4,000,000							4,000,000
GE Warrant \| Tranche A Loans
Stockholders' equity
Number of shares that will become exercisable at the time the specified loan is made under the credit agreement		1,250,000						1,250,000
Number of additional shares that will become exercisable at the time that specified loan of at least $15,000,000 principal amount is made under the credit agreement		1,000,000						750,000
Minimum specified principal amount for additional shares to become exercisable \| $		$ 15,000						$ 15,000
GE Warrant \| Tranche B Loans
Stockholders' equity
Number of shares that will become exercisable at the time the specified loan is made under the credit agreement		1,250,000						1,250,000
Number of additional shares that will become exercisable at the time that specified loan of at least $15,000,000 principal amount is made under the credit agreement		1,000,000						750,000
Minimum specified principal amount for additional shares to become exercisable \| $		$ 15,000						$ 15,000
Common stock
Stockholders' equity
Number of shares of the company's common stock in a unit											1
Number of shares issued for units under Placement Agent Agreement					4,419,192
Proceeds after deducting the placement agent's fees and other offering expenses related to the sale of units \| $					$ 19,166
Exercise price of the warrant (in dollars per share) \| $ / shares		$ 0.01
Common stock \| GE Warrant \| GE Credit Agreement
Stockholders' equity
Number of shares that can be purchased upon exercise of warrants		5,000,000
Maximum \| Series I Warrants
Stockholders' equity
Number of shares that can be purchased upon exercise of each warrant											0.75
Maximum \| Series II Warrant
Stockholders' equity
Number of shares that can be purchased upon exercise of each warrant											0.2571

Stockholders' Equity (Details 3) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation
Stock-based compensation expense	$ 11,514	$ 23,008	$ 22,087
Stock-based compensation expense, net of tax	$ 11,514	23,008	22,087
2002 Plan \| Stock Options
Stock-based compensation
Award term	10 years
Percentage ownership of stock for which the option purchase price will be 110% of fair market	10.00%
Vesting period	3 years
2002 Plan \| Stock Options \| Minimum
Stock-based compensation
Purchase price of options expressed as percentage of fair market value of common stock	100.00%
Purchase price of options granted to 10% stockholders expressed as percentage of fair market value of common stock	110.00%
2006 Plan \| Stock Options
Stock-based compensation
Stock-based compensation expense	$ 7,286	$ 13,751	14,199
Number of shares reserved for issuance	18,890,500
Number of shares available for future grant	779,127
Number of Shares
Outstanding at the beginning of the period	11,526,998
Options granted	957,000
Options exercised	(468,279)
Options forfeited	(529,418)
Outstanding at the end of the period	11,486,301	11,526,998
Exercisable at the end of the period	9,875,201
Weighted Average Exercise Price
Outstanding at the beginning of the period	$ 11.79
Options granted	10.23
Options exercised	3.78
Options forfeited	13.40
Outstanding at the end of the period	11.91	$ 11.79
Exercisable at the end of the period	$ 11.94
Additional option disclosures
Options outstanding at the end of the period, weighted average remaining contractual term	5 years 15 days
Options exercisable at the end of the period, weighted average remaining contractual term	4 years 5 months 16 days
Other disclosures
Total unrecognized compensation cost related to non-vested shares	$ 6,967
Weighted average period over which the total unrecognized compensation cost related to non-vested shares is expected to be recognized	1 year 6 months
Total fair value of shares vested	$ 8,101
Intrinsic value of all options exercised	$ 2,568	$ 935	$ 18,822
Weighted-average assumption used for grants
Dividend yield	0.00%
Expected volatility, minimum	52.30%
Expected volatility, maximum	67.00%
Risk-free interest rate, minimum	1.10%
Risk-free interest rate, maximum	1.80%
Expected life	6 years
Stock-based compensation
Weighted-average grant date fair values of options granted	$ 5.32	$ 6.86	$ 7.95

Stockholders' Equity (Details 4) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended			36 Months Ended
	Feb. 02, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Stock-based compensation
Stock-based compensation expense		$ 11,514	$ 23,008	$ 22,087
Market-Based RSUs
Stock-based compensation
Number of shares of common stock to be received for each performance unit		1
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the closing price on the grant date in order for a holder to receive one share of common stock for each award		20 days
Percentage of the closing price of the entity's common stock that the closing price must equal or exceed in order for an award holder to receive one share of common stock for each award		135.00%
Period from the date of grant after which awards will be automatically forfeited if the Stock Price Condition is not satisfied		4 years
Number of Shares
Outstanding at the beginning of the period		1,545,000
RSUs granted		489,500			2,034,500
RSUs forfeited		(265,500)
Outstanding at the end of the period		1,769,000	1,545,000		1,769,000
Weighted Average Fair Value at Grant Date
Outstanding at the beginning of the period		$ 11.42
RSUs granted		8.26
RSUs forfeited (in dollars per share)		10.62
Outstanding at the end of the period		$ 10.67	$ 11.42		$ 10.67
Weighted Average Remaining Contractual Term		1 year 6 months 26 days
Stock-based compensation
Total unrecognized compensation cost related to non-vested shares		$ 2,191			$ 2,191
Weighted average period over which the total unrecognized compensation cost related to non-vested shares is expected to be recognized		1 year 1 month 6 days
Stock-based compensation expense		$ 2,556	$ 8,821
Weighted-average assumption used for grants
Dividend yield	0.00%
Expected volatility	47.00%
Risk-free interest rate	1.10%
Expected life	2 years
Market-Based RSUs \| Minimum
Stock-based compensation
Period from the date of grant in which the closing price of the entity's common stock must exceed the closing price in order for a holder to receive one share of common stock for each award		2 years
Market-Based RSUs \| Maximum
Stock-based compensation
Period from the date of grant in which the closing price of the entity's common stock must exceed the closing price in order for a holder to receive one share of common stock for each award		4 years
Service-Based RSUs
Stock-based compensation
Vesting period		3 years
Number of Shares
Outstanding at the beginning of the period		45,836
RSUs granted		792,500
RSUs vested		(15,584)
Outstanding at the end of the period		822,752	45,836		822,752
Weighted Average Fair Value at Grant Date
Outstanding at the beginning of the period		$ 13.09
RSUs granted		5.54
RSUs vested (in dollars per share)		13.09
Outstanding at the end of the period		$ 5.82	$ 13.09		$ 5.82
Weighted Average Remaining Contractual Term		2 years 10 months 6 days
Stock-based compensation
Total unrecognized compensation cost related to non-vested shares		$ 4,186			$ 4,186
Weighted average period over which the total unrecognized compensation cost related to non-vested shares is expected to be recognized		2 years 9 months 18 days
Stock-based compensation expense		$ 365	$ 51
Service-Based RSUs \| Vesting over the first year
Stock-based compensation
Vesting percentage		34.00%
Service-Based RSUs \| Vesting over the second year
Stock-based compensation
Vesting percentage		33.00%
Service-Based RSUs \| Vesting over the third year
Stock-based compensation
Vesting percentage		33.00%

Stockholders' Equity (Details 5) $ in Thousands	12 Months Ended
Stockholders' Equity (Details 5) $ in Thousands	Dec. 31, 2014 USD ($) item shares	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Stock-based compensation
Stock-based compensation expense \| $	$ 11,514	$ 23,008	$ 22,087
Employee Stock Purchase Plan
Stock-based compensation
Purchase price of shares expressed as percentage of fair market value of common stock	85.00%
Number of non-concurrent offering periods \| item	2
Number of shares reserved \| shares	2,500,000
Stock-based compensation expense \| $	$ 67	$ 29
Shares sold pursuant to the ESPP \| shares	57,881

Stockholders' Equity (Details 6) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation
Stock-based compensation expense		$ 11,514	$ 23,008	$ 22,087
CERF Plan \| Stock Options
Stock-based compensation
Number of shares reserved for issuance	150,000
Number of Shares
Outstanding at the beginning of the period		115,000
Outstanding at the end of the period		115,000	115,000
Weighted Average Exercise Price
Outstanding at the beginning of the period		$ 40.80
Outstanding at the end of the period		$ 40.80	$ 40.80
Additional option disclosures
Options outstanding at the end of the period, weighted average remaining contractual term		8 years 8 months 19 days
Other disclosures
Total unrecognized compensation cost related to non-vested units		$ 2,070
Weighted average period over which the total unrecognized compensation cost related to non-vested units is expected to be recognized		1 year 9 months 18 days
Weighted-average assumption used for grants
Dividend yield		0.00%
Expected volatility		96.40%
Risk-free interest rate		1.90%
Expected life		6 years
Stock-based compensation
Weighted-average grant date fair values of options granted	$ 31.65
Stock-based compensation expense		$ 1,240	$ 356

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of loss before income taxes
U.S.	$ (64,913)	$ (40,195)	$ (91,608)
Foreign	(24,871)	(23,009)	(7,960)
Income (loss) before income taxes, total	(89,784)	(63,204)	(99,568)
Current:
Current Federal	190	87	269
Current State	238	310	302
Current Foreign	1,017	2,910	(61)
Total current	1,445	3,307	510
Deferred:
Federal	29	134
State	(10)	47
Foreign	(389)	227	784
Total deferred	(370)	408	784
Income tax expense (benefit)	$ 1,075	$ 3,715	$ 1,294
Reconciliation of the income tax provision
Federal income tax rate (as a percent)	35.00%	35.00%	35.00%
Computed expected tax expense (benefit)	$ (30,415)	$ (22,121)	$ (34,849)
Nondeductible expenses	10,690	7,216	5,194
Tax rate differential on foreign earnings	5,733	2,993	(717)
Basis difference on sale		(6,457)
Tax credits	(8,286)	(35,604)
Other	(1,121)	82	(1,442)
Change in valuation allowance	24,474	57,606	33,108
Income tax expense (benefit)	1,075	3,715	$ 1,294
Tax benefit related to exclusion of VETC associated with 2013 fuel sales	8,221	7,068
Tax benefit related to exclusion of VETC associated with 2006 to 2012 fuel sales		27,497
Deferred tax assets:
Accrued expenses	4,834	3,367
Sales-type leases	908	997
Alternative minimum tax and general business credits	4,966	4,903
Derivative loss	527	1,161
Stock option expense	21,741	20,832
Other	2,596	4,693
Loss carryforwards	147,706	126,563
Total deferred tax assets	183,278	162,516
Less valuation allowance	(160,436)	(136,969)
Net deferred tax assets	22,842	25,547
Deferred tax liabilities:
Depreciation and amortization	(20,028)	(21,800)
Goodwill	3,864	1,626
Partnership income		(3,540)
Total deferred tax liabilities	(23,892)	(26,966)
Net deferred tax liabilities	$ (1,050)	$ (1,419)

Income Taxes (Details 2) $ in Thousands	Dec. 31, 2014 USD ($)
Federal
Income Taxes
Operating loss carryforwards	$ 369,332
Federal \| General
Income Taxes
Tax credit carryforwards	4,750
State
Income Taxes
Operating loss carryforwards	284,828
Foreign
Income Taxes
Operating loss carryforwards	$ 50,334

Income Taxes (Details 3) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details 3) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation allowance
Valuation allowance	$ 160,436	$ 136,969
Net change in valuation allowance.	23,468	55,711
Undistributed earnings of non-U.S. subsidiaries	3,327
Unrecognized tax benefits, which if recognized, would primarily affect the effective tax rate	692
Unrecognized tax benefits, which if recognized, would increase the net operating loss carryforwards	21,282
Reconciliation of the total amounts of unrecognized tax benefits
Unrecognized tax benefit at the beginning of the period	17,398	515
Gross increases-tax positions in current year	4,722	16,685
Gross increases-tax positions in prior years	(146)	198
Unrecognized tax benefit at the end of the period	21,974	17,398	$ 515
Additional information on income tax
Interest accrued	$ 120	$ 75	$ 21

Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fiscal year:
2015	$ 10,343
2016	9,124
2017	7,492
2018	5,348
2019	5,153
Thereafter	21,958
Total future minimum lease payments	59,418
Rent expense	$ 10,140	$ 10,504	$ 7,737

Commitments and Contingencies (Details 2) - LNG sales agreement - DGS $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2007 gal / d	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Mar. 01, 2014 gal / d
Long-Term Take-or-pay Contracts
Purchase period	10 years
Number of gallons of LNG per day \| gal / d	45,000				65,000
Amount paid under the contract		$ 14,267	$ 11,404	$ 8,153
Fixed commitments under the contract payable in future
2015		7,974
2016		4,628
2017		$ 3,857

Geographic Information (Details) - USD ($) $ in Thousands	12 Months Ended
Geographic Information (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Geographic Information
Total revenue	$ 428,940	$ 352,475	$ 334,008
Total operating income (loss)	(54,364)	(51,691)	(70,522)
Total long-lived assets	674,866	656,172	605,905
United States
Geographic Information
Total revenue	360,881	292,250	286,125
Total operating income (loss)	(41,543)	(44,797)	(69,030)
Total long-lived assets	582,028	544,638	480,067
Canada
Geographic Information
Total revenue	16,241	13,922	8,364
Total operating income (loss)	(3,087)	(1,594)	(188)
Total long-lived assets	85,984	103,997	122,291
Other
Geographic Information
Total revenue	51,818	46,303	39,519
Total operating income (loss)	(9,734)	(5,300)	(1,304)
Total long-lived assets	$ 6,854	$ 7,537	$ 3,547

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
401(k) Plan
Maximum percentage of base pay that can be contributed by employees through salary deferrals	90.00%
Contribution by the company	$ 1,040	$ 1,448	$ 1,289

Supplier Concentrations (Details) - Natural gas expense - Supplier concentration	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Williams Gas Processing Company
Supplier Concentrations
Concentration risk (as a percent)	4.00%	3.00%	8.00%
Shell Energy
Supplier Concentrations
Concentration risk (as a percent)	17.00%	22.00%	31.00%
SoCal Gas Company And San Diego Gas And Electric
Supplier Concentrations
Concentration risk (as a percent)	3.00%	7.00%	16.00%
BP Energy
Supplier Concentrations
Concentration risk (as a percent)	24.00%

Capitalized Lease Obligation and Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Dec. 31, 2013
Capitalized Lease Obligation and Receivables
Weighted average interest rate (as a percent)	15.02%
Future payments under these capital leases
2015	$ 1,006
2016	644
2017	686
2018	365
2019	357
Thereafter	938
Total minimum lease payments	3,996
Less amount representing interest	(1,304)
Present value of future minimum lease payments	2,692
Less current portion	(700)
Capital lease obligations, less current portion	1,992
Value of the equipment under capital lease	4,898	$ 6,802
Accumulated amortization	$ 1,936	$ 4,185

Capitalized Lease Obligation and Receivables (Details 2) $ in Thousands	Dec. 31, 2014 USD ($)
Capitalized Lease Obligation and Receivables
Sales-type leases interest rate (as a percent)	4.37%
Future receipts under the leases
2015	$ 487
2016	395
2017	194
2018	65
Total	1,141
Less amount representing interest	(70)
Present value of future minimum lease receipts	$ 1,071

Fair Value Measurements (Details) - Fair value measured on recurring basis - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements
Estimated remaining life of Series I warrants	1 year 3 months 29 days
Liabilities:
Contingent consideration obligation		$ 384
Minimum
Fair Value Measurements
Term of traded options	3 months
Maximum
Fair Value Measurements
Term of traded options	9 months
Certificates of deposit
Assets:
Available-for-sale securities	$ 35,355	35,621
Municipal bonds and notes
Assets:
Available-for-sale securities	38,652	59,795
Corporate bonds
Assets:
Available-for-sale securities	45,233	42,824
Zero coupon bonds
Assets:
Available-for-sale securities	3,306
Series I Warrants
Liabilities:
Derivative liability	1,416	7,164
Level 2 \| Certificates of deposit
Assets:
Available-for-sale securities	35,355	35,621
Level 2 \| Municipal bonds and notes
Assets:
Available-for-sale securities	38,652	59,795
Level 2 \| Corporate bonds
Assets:
Available-for-sale securities	45,233	42,824
Level 2 \| Zero coupon bonds
Assets:
Available-for-sale securities	3,306
Level 3
Liabilities:
Contingent consideration obligation		384
Level 3 \| Series I Warrants
Liabilities:
Derivative liability	$ 1,416	$ 7,164

Fair Value Measurements (Details 2) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013
Other disclosures
Impairment of long-lived assets		$ 4,772
VPG
Other disclosures
Impairment of long-lived assets	$ 4,772
Contingent Consideration Liabilities
Reconciliation of the beginning and ending balances of items measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance		384	$ 1,516
Gain included in earnings		(208)	(1,132)
Payments		(176)
Ending Balance	1,516		384
Series I Warrant Liabilities
Reconciliation of the beginning and ending balances of items measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance		7,164	8,102
Gain included in earnings		(5,748)	(938)
Ending Balance	$ 8,102	$ 1,416	$ 7,164

Fair Value Measurements (Details 3) - Level 3 - Series I Warrant Liabilities - Black-Scholes Model	12 Months Ended
	Dec. 31, 2014 $ / shares
Unobservable Input
Current market price of the Company's common stock (in dollars per share)	$ 5.00
Exercise price of the warrant (in dollars per share)	$ 12.68
Dividend yield (as a percent)	0.00%
Remaining term of the warrant	1 year 3 months 29 days
Minimum
Unobservable Input
Implied volatility of the Company's common stock (as a percent)	85.00%
Maximum
Unobservable Input
Implied volatility of the Company's common stock (as a percent)	85.90%
Simple average
Unobservable Input
Discount rate (as a percent)	0.46%

Schedule II: Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowances for Doubtful Trade Receivables
Movement in valuation and qualifying accounts
Balance at the beginning of the period	$ 832	$ 905	$ 712
Charges (benefit) to operations	387	454	435
Deductions	(467)	(527)	(242)
Balance at the end of the period	752	832	905
Allowance for Doubtful Notes Receivables
Movement in valuation and qualifying accounts
Balance at the beginning of the period	2,416	909	20
Charges (benefit) to operations	890	1,507	924
Deductions	(456)		(35)
Balance at the end of the period	$ 2,850	$ 2,416	$ 909