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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 31, 2018
Document and Entity Information
Entity Registrant Name	Clean Energy Fuels Corp.
Entity Central Index Key	0001368265
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		203,472,977
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash, cash equivalents and restricted cash	$ 160,020	$ 37,208
Short-term investments	95,964	141,462
Accounts receivable, net of allowance for doubtful accounts of $1,276 and $1,507 as of December 31, 2017 and September 30, 2018, respectively	69,822	63,961
Other receivables	17,890	19,235
Inventory	37,103	35,238
Prepaid expenses and other current assets	8,096	7,793
Total current assets	388,895	304,897
Land, property and equipment, net	344,077	367,305
Notes receivable and other long-term assets, net	15,978	21,397
Investments in other entities	27,674	30,395
Goodwill	64,328	64,328
Intangible assets, net	2,478	3,590
Total assets	843,430	791,912
Current liabilities:
Current portion of debt and capital lease obligations	115,879	139,699
Accounts payable	12,849	17,901
Accrued liabilities	48,322	42,268
Deferred revenue	8,830	3,432
Total current liabilities	185,880	203,300
Long-term portion of debt and capital lease obligations	122,817	120,388
Other long-term liabilities	15,348	18,566
Total liabilities	324,045	342,254
Commitments and contingencies (Note 18)
Stockholders’ equity:
Preferred stock, $0.0001 par value. Authorized 1,000,000 shares; issued and outstanding no shares	0	0
Common stock, $0.0001 par value. Authorized 224,000,000 shares and 304,000,000 shares as of December 31, 2017 and September 30, 2018, respectively; issued and outstanding 151,650,969 shares and 203,472,977 shares as of December 31, 2017 and September 30, 2018, respectively	20	15
Additional paid-in capital	1,196,720	1,111,432
Accumulated deficit	(695,515)	(683,570)
Accumulated other comprehensive loss	(273)	(887)
Total Clean Energy Fuels Corp. stockholders’ equity	500,952	426,990
Noncontrolling interest in subsidiary	18,433	22,668
Total stockholders’ equity	519,385	449,658
Total liabilities and stockholders’ equity	$ 843,430	$ 791,912

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,507	$ 1,276
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	304,000,000	224,000,000
Common stock, issued (in shares)	203,472,977	151,650,969
Common stock, outstanding (in shares)	203,472,977	151,650,969

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue:
Total revenue	$ 77,320	$ 81,792	$ 250,190	$ 252,299
Cost of sales (exclusive of depreciation and amortization shown separately below):
Inventory valuation provision	0	13,158	0	13,158
Selling, general and administrative	18,396	24,798	57,101	71,875
Depreciation and amortization	13,363	14,104	39,496	43,757
Asset impairments and other charges	0	60,666	0	60,666
Total operating expenses	84,565	172,893	249,850	367,828
Operating income (loss)	(7,245)	(91,101)	340	(115,529)
Interest expense	(4,096)	(4,270)	(13,126)	(13,466)
Interest income	1,129	465	2,193	1,156
Other income (expense), net	(193)	4	(126)	(28)
Loss from equity method investments	(542)	(30)	(2,739)	(100)
Gain from extinguishment of debt	0	0	0	3,195
Gain from sale of certain assets of subsidiary	0	0	0	69,886
Loss from formation of equity method investment	(1,163)	0	(1,163)	0
Loss before income taxes	(12,110)	(94,932)	(14,621)	(54,886)
Income tax benefit (expense)	(89)	44	(266)	2,183
Net loss	(12,199)	(94,888)	(14,887)	(52,703)
Loss attributable to noncontrolling interest	1,300	747	4,235	1,813
Net loss attributable to Clean Energy Fuels Corp.	$ (10,899)	$ (94,141)	$ (10,652)	$ (50,890)
Loss per share:
Basic (in dollars per share)	$ (0.05)	$ (0.62)	$ (0.06)	$ (0.34)
Diluted (in dollars per share)	$ (0.05)	$ (0.62)	$ (0.06)	$ (0.34)
Weighted-average common shares outstanding:
Basic (in shares)	203,469,222	150,927,825	172,946,896	150,128,204
Diluted (in shares)	203,469,222	150,927,825	172,946,896	150,128,204
Product revenue
Revenue:
Total revenue	$ 67,441	$ 67,669	$ 220,812	$ 211,747
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	48,063	52,884	139,658	158,306
Service revenue
Revenue:
Total revenue	9,879	14,123	29,378	40,552
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	$ 4,743	$ 7,283	$ 13,595	$ 20,066

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net loss	$ (12,199)	$ (94,888)	$ (14,887)	$ (52,703)
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2017 and 2018	59	252	(45)	289
Foreign currency adjustments on intra-entity long-term investments, net of $0 tax in 2017 and 2018	0	2,919	0	5,033
Unrealized gains (losses) on available-for-sale securities, net of $0 tax in 2017 and 2018	56	70	659	(39)
Total other comprehensive income	115	3,241	614	5,283
Comprehensive loss	(12,084)	(91,647)	(14,273)	(47,420)
Clean Energy Fuels Corp.
Net loss	(10,899)	(94,141)	(10,652)	(50,890)
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2017 and 2018	59	252	(45)	289
Foreign currency adjustments on intra-entity long-term investments, net of $0 tax in 2017 and 2018	0	2,919	0	5,033
Unrealized gains (losses) on available-for-sale securities, net of $0 tax in 2017 and 2018	56	70	659	(39)
Total other comprehensive income	115	3,241	614	5,283
Comprehensive loss	(10,784)	(90,900)	(10,038)	(45,607)
Noncontrolling Interest
Net loss	(1,300)	(747)	(4,235)	(1,813)
Other comprehensive income, net of tax:
Comprehensive loss	$ (1,300)	$ (747)	$ (4,235)	$ (1,813)

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Condensed Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, tax	$ 0	$ 0	$ 0	$ 0
Foreign currency adjustments on intra-entity long-term investments, tax	0	0	0	0
Unrealized (losses) gains on available-for-sale securities, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (14,887)	$ (52,703)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	39,496	43,757
Provision for doubtful accounts, notes and inventory	1,294	16,156
Stock-based compensation expense	4,312	6,604
Amortization of discount and debt issuance cost	55	973
Loss on disposal of property and equipment	1,210	2,500
Gain on extinguishment of debt	0	(3,195)
Gain from sale of certain assets of subsidiary	0	(69,886)
Loss from formation of equity method investment	1,163	0
Loss from equity method investments	2,739	100
Asset impairments and other charges	0	58,119
Changes in operating assets and liabilities:
Accounts and other receivables	(6,605)	23,936
Inventory	(2,403)	494
Prepaid expenses and other assets	260	1,914
Accounts payable	(2,374)	(9,426)
Deferred revenue	2,790	(550)
Accrued expenses and other	1,954	(22,198)
Net cash provided by (used in) operating activities	29,004	(3,405)
Cash flows from investing activities:
Purchases of short-term investments	(293,599)	(227,212)
Maturities and sales of short-term investments	340,284	149,044
Purchases of and deposits on property and equipment	(14,209)	(27,529)
Loans made to customers	0	(535)
Payments on and proceeds from sales of loans receivable	388	978
Cash received from sale of certain assets of subsidiary, net of cash, cash equivalents and restricted cash transferred	871	149,088
Investments in other entities	0	(1,929)
Proceeds from disposal of property and equipment	530	0
Nonrefundable customer deposit	0	8,350
Net cash provided by investing activities	34,265	50,255
Cash flows from financing activities:
Issuances of common stock	83,433	10,767
Fees paid for issuances of common stock and debt issuance costs	(993)	(638)
Payment to holders of stock options in subsidiary	0	(8,605)
Proceeds from debt instruments	8,243	7,561
Proceeds from revolving line of credit	0	308
Repayment of borrowing under revolving line of credit	0	(23,670)
Repayment of capital lease obligations and debt instruments	(31,066)	(29,664)
Net cash provided by (used in) financing activities	59,617	(43,941)
Effect of exchange rates on cash, cash equivalents and restricted cash	(74)	751
Net increase in cash, cash equivalents and restricted cash	122,812	3,660
Cash, cash equivalents and restricted cash, beginning of period	37,208	43,115
Cash, cash equivalents and restricted cash, end of period	160,020	46,775
Supplemental disclosure of cash flow information:
Income taxes paid	171	363
Interest paid, net of approximately $73 and $169 capitalized, respectively	$ 9,182	$ 14,351

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Interest paid, capitalized	$ 169	$ 73

General	9 Months Ended
General	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General Nature of Business Clean Energy Fuels Corp., together with its majority and wholly owned subsidiaries (hereinafter collectively referred to as the “Company,” unless the context or the use of the term indicates or requires otherwise) is engaged in the business of selling natural gas as an alternative fuel for vehicle fleets and related natural gas fueling solutions to its customers, primarily in the United States and Canada. The Company’s principal business is supplying renewable natural gas (“RNG”), compressed natural gas (“CNG”) and liquefied natural gas (“LNG”) (RNG can be delivered in the form of CNG or LNG) for light, medium and heavy-duty vehicles and providing operation and maintenance (“O&M”) services for public and private vehicle fleet customer stations. As a comprehensive solution provider, the Company also designs, builds, operates and maintains fueling stations; sells and services natural gas fueling compressors and other equipment used in CNG stations and LNG stations; offers assessment, design and modification solutions to provide operators with code-compliant service and maintenance facilities for natural gas vehicle fleets; transports and sells CNG and LNG via “virtual” natural gas pipelines and interconnects; procures and sells RNG; sells tradable credits it generates by selling RNG and conventional natural gas as a vehicle fuel, including Renewable Identification Numbers (“RIN Credits” or “RINs”) under the federal Renewable Fuel Standard Phase 2 and credits under the California and the Oregon Low Carbon Fuel Standards (collectively, “LCFS Credits”); helps its customers acquire and finance natural gas vehicles; and obtains federal, state and local credits, grants and incentives. In addition, for all periods presented before March 31, 2017, the Company produced RNG at its own production facilities, and for all periods presented before December 29, 2017, the Company manufactured natural gas fueling compressors and other equipment used in CNG stations. See Notes 4 and 5 for more information. Basis of Presentation The accompanying interim unaudited condensed 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 consolidated financial position as of September 30, 2018, and results of operations and comprehensive loss for the three and nine months ended September 30, 2017 and 2018, and cash flows for the nine months ended September 30, 2017 and 2018. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and nine month periods ended September 30, 2017 and 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other interim period or for any future year. Certain information and disclosures normally included in the notes to consolidated financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”), but the resultant disclosures contained herein are in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) as they apply to interim reporting. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2017 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 13, 2018. Reclassifications During the nine months ended September 30, 2018, the Company adopted Accounting Standards Update (“ASU”) No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (see Note 20). The new standard requires restricted cash and restricted cash equivalents to be included as components of total cash and cash equivalents as presented on the statement of cash flows. As a result, the Company chose to also conform this classification on the accompanying condensed consolidated balance sheets. This resulted in prior period restricted cash of $1,127 as of December 31, 2017 being reclassified into one line item with cash and cash equivalents to conform to presentation as of September 30, 2018. In addition, certain prior period amounts have been reclassified in the condensed consolidated statements of cash flows to conform to the current period presentation. These reclassifications had no material impact on the Company’s consolidated financial position, results of operations, or cash flows as previously reported. Use of Estimates The preparation of condensed consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying condensed consolidated financial statements and these notes. Actual results could differ from those estimates and may result in material effects on the Company’s operating results and financial position. Significant estimates made in preparing the accompanying condensed consolidated financial statements include (but are not limited to) those related to revenue recognition, goodwill and long-lived asset impairment assessments, income tax valuations and fair value measurements.

Revenue from Contracts with Customers

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenue from Contracts with Customers

Revenue Recognition Overview

The Company recognizes revenue when control of the promised goods or services is transferred to its customers, in an amount that reflects the consideration to which it expects to be entitled in exchange for the goods or services. In order to achieve that core principle, a five-step approach is applied: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue allocated to each performance obligation when the Company satisfies the performance obligation. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer, and is the unit of account for revenue recognition.

The table below presents the Company’s revenues disaggregated by revenue source. The Company is generally the principal in its customer contracts as it has control over the goods and services prior to them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities.



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2018		2017		2018
Volume -related	$	63,123	$	67,827	$	199,987	$	197,805
Station construction sales	12,502		9,359		34,077		20,938
Alternative fuels excise tax credit (“AFTC”)	—		—		—		26,863
Compressor sales	5,919		—		17,640		—
Other	248		134		595		4,584
	$	81,792	$	77,320	$	252,299	$	250,190

Volume -Related

The Company’s volume -related revenue primarily consists of sales of RNG, CNG and LNG fuel, O&M services and RINs and LCFS Credits.

Fuel and O&M services are sold pursuant to contractual commitments over defined goods -and -service delivery periods. These contracts typically include a stand -ready obligation to supply natural gas and/or provide O&M services daily based on a committed and agreed upon routine maintenance schedule or when and if called upon by the customer.

The Company recognizes fuel and O&M services revenue in the amount to which the Company has the right to invoice. The Company has a right to consideration based on the amount of gasoline gallon equivalents of natural gas dispensed by the customer and current pricing conditions, which are typically billed to the customer on a monthly basis. Since payment terms are less than a year, the Company has elected the practical expedient which allows it to not assess whether a customer contract has a significant financing component.

Contract modifications are not distinct from the existing contract and are typically renewals of fuel and O&M service sales. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price is recognized prospectively.

The Company sells RINs and LCFS Credits (the “government credits”) to third parties that need the credits to comply with federal and state requirements. The government credits are considered variable consideration because they can either increase or decrease the transaction price based on volumes of vehicle fuel sold. Additionally, these government credits are constrained until there is an agreement in place to monetize the credits at a determinable price. Upon entering into such an agreement, the government credits are recognized as the constraint is removed.

Station Construction Sales

Station construction contracts are generally short-term, except for certain larger and more complex stations, which can take up to 24 months to complete. For most of the Company’s station construction contracts, the customer contracts with the Company to provide a significant service of integrating a complex set of tasks and components into a single station. Hence, the entire contract is accounted for as one performance obligation.

The Company generally recognizes revenue over time as the Company performs under its station construction contracts because of the continual transfer of control of the goods to the customer, who typically controls the work in process. Revenue is recognized based on the extent of progress towards completion of the performance obligation and is recorded proportionally as costs are incurred. Costs to fulfill the Company’s obligations under these contracts typically include labor, materials and subcontractors’ costs, other direct costs and an allocation of indirect costs.

Refinements of estimates to account for changing conditions and new developments are continuous and characteristic of the process. Many factors that can affect contract profitability may change during the performance period of the contract, including differing site conditions, the availability of skilled contract labor, the performance of major suppliers and subcontractors, and unexpected changes in material costs. Because a significant change in one or more of these estimates could affect the profitability of these contracts, the contract price and cost estimates are reviewed periodically as work progresses and adjustments proportionate to the cost-to-cost measure of progress are reflected in contract revenues in the reporting period when such estimates are revised as discussed above. Provisions for estimated losses on uncompleted contracts are recorded in the period in which the losses become known.

Contract modifications are typically expansions in scope of an existing station construction project. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price and the Company’s measure of progress for the performance obligation to which it relates is recognized as an adjustment to revenue (either as an increase or a reduction) on a cumulative catch-up basis.

Under the typical payment terms of the Company’s station construction contracts, the customer makes either performance-based payments (“PBPs”) or progress payments. PBPs are interim payments of the contract price based on quantifiable measures of performance or the achievement of specified events or milestones. Progress payments are interim payments of costs incurred as the work progresses. For some of these contracts, the Company may be entitled to receive an advance payment. The advance payment typically is not considered a significant financing component because it is used to meet working capital demands that can be higher in the early stages of a construction contract and to protect the Company if the customer fails to adequately complete some or all of its obligations under the contract. In addition, the customer retains a small portion of the contract price until completion of the contract. Such retained portion of the contract price is not considered a significant financing component because the intent is to protect the customer.

In certain contracts with its customers, the Company agrees to provide multiple goods or services, including construction of and sale of a station, O&M services, and sale of fuel to the customer. These contracts have multiple performance obligations because the promise to transfer each separate good or service is separately identifiable and is distinct. This evaluation requires significant judgment and the decision to combine a group of contracts or separate the combined or single contract into multiple performance obligations could change the amount of revenue recognized in one or more periods.

The Company allocates the contract price to each performance obligation using best estimates of the standalone selling price of each distinct good or service in the contract. The primary method used to estimate the standalone selling price for fuel and O&M services is observable standalone sales, and the primary method used to estimate the standalone selling price for station construction sales is the expected cost plus a margin approach because the Company sells customized customer -specific solutions. Under this approach, the Company forecasts expected costs of satisfying a performance obligation and then adds an appropriate margin for the good or service.

AFTC

See Note 19 for more information about AFTC. AFTC is considered variable consideration because it can either increase or decrease the transaction price based on volumes of vehicle fuel sold. Additionally, AFTC is not recognized as revenue until it is authorized through federal legislation, which also provides a determinable price. The Company recognizes revenue in the period the credit is authorized through federal legislation.

Compressor Sales

The Company completed the CEC Combination (as defined in Note 5) during the year ended December 31, 2017 and no longer generates revenue from compressor sales.

Other

The majority of other revenue is from sales of used natural gas heavy -duty trucks purchased by the Company. Revenue on these contracts is recognized at the point in time when the customer accepts delivery of the truck.

Remaining Performance Obligations

Remaining performance obligations represents the transaction price of customer orders for which the work has not been performed. As of September 30, 2018, the aggregate amount of the transaction price allocated to remaining performance obligations was $11,316, which related to the Company’s station construction sale contracts. The Company expects to recognize revenue on the remaining performance obligations under these contracts over the next 12 to 24 months.

For volume -related revenue, the Company has elected to apply an optional exemption, which waives the requirement to disclose the remaining performance obligation for revenue recognized through the “right to invoice” practical expedient.

Costs to Fulfill a Contract

The Company capitalizes costs incurred to fulfill its contracts that (1) relate directly to the contract, (2) are expected to generate resources that will be used to satisfy the Company’s performance obligations under the contract, and (3) are expected to be recovered through revenue generated under the contract. Contract fulfillment costs are recorded to depreciation expense as the Company satisfies its performance obligations over the term of the contract. These costs primarily relate to set-up and other direct installation costs incurred by the Company’s subsidiary, NG Advantage LLC (“NG Advantage”), for equipment that must be installed on customers’ land before NG Advantage is able to deliver CNG to the customer because the customer does not have direct access to the natural gas pipelines. These costs are classified in “Land, property, and equipment, net” in the accompanying condensed consolidated balance sheets. As of September 30, 2018, these capitalized costs incurred to fulfill contracts were $7,270 with accumulated depreciation of $4,495 and related amortization of $484 and $1,490 for the three and nine months ended September 30, 2018.

Contract Balances

The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets), and customer advances and deposits (contract liabilities) in the accompanying condensed consolidated balance sheets. Changes in the contract asset and liability balances during the nine months ended September 30, 2018, were not materially impacted by any factors outside the normal course of business.

As of December 31, 2017 and September 30, 2018, the Company’s contract balances were as follows:



	December 31, 2017		September 30, 2018
Receivables, net	$	63,961	$	69,822

Contract Assets - Current	$	1,603	$	550
Contract Assets - Noncurrent	5,046		3,890
Contract Assets - Total	$	6,649	$	4,440

Contract Liabilities - Current	$	3,432	$	8,830
Contract Liabilities - Noncurrent	13,413		10,682
Contract Liabilities - Total	$	16,845	$	19,512

Receivables, Net

“Receivables, net” in the accompanying condensed consolidated balance sheets include amounts billed and currently due from customers. The amounts due are stated at their net estimated realizable value. The Company maintains an allowance for doubtful accounts to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of customer creditworthiness, historical payment experience, and the age of outstanding receivables.

Contract Assets

Contract assets include unbilled amounts typically resulting from the Company’s station construction sale contracts, when the cost-to-cost method of revenue recognition is utilized and revenue recognized exceeds the amount billed to the customer, and right to payment is not just subject to the passage of time. Amounts may not exceed their net realizable value. Contract assets are classified as current or noncurrent based on the timing of billings. The current portion is included in “Prepaid expenses and other current assets” and the noncurrent portion is included in “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets.

Contract Liabilities

Contract liabilities consist of billings in excess of revenue recognized from the Company’s station construction sale contracts and deferred revenue when cash payments are received or due in advance of the Company’s performance obligation, which are generally for the Company’s volume -related revenue contracts. Billings in excess of revenue recognized of $1,092 and $3,255 are classified as current and are included in “Deferred revenue” in the accompanying condensed consolidated balance sheets as of December 31, 2017 and September 30, 2018, respectively. Deferred revenue is classified as current or noncurrent based on when the revenue is expected to be recognized. The noncurrent portion of deferred revenue is included in “Other long -term liabilities” in the accompanying condensed consolidated balance sheets.

The increase in the contract liabilities balance for the nine months ended September 30, 2018 is primarily driven by billings in excess of revenue recognized, offset by $1,636 of revenue recognized related to the Company’s contract liability balances as of December 31, 2017.

Asset Impairments, Other Charges, and Inventory Valuation Provision

9 Months Ended

Sep. 30, 2018

Restructuring and Related Activities [Abstract]

Asset Impairments, Other Charges, and Inventory Valuation Provision

In light of continuing low oil prices and the current state of natural gas vehicle adoption, among other factors, during the three months ended September 30, 2017, the Company undertook an evaluation of its operations with the intent of minimizing and eliminating assets it believed were underperforming. As a result of this evaluation, the Company identified certain of its fueling stations where the current and projected natural gas volume and profitability levels were not expected to be sufficient to support the Company’s investment in the fueling station assets, and the Company decided to close these stations. The Company also reduced its workforce and took other steps to reduce overhead costs as a result of this evaluation, in an effort to lower its operating expenses going forward. In addition, this evaluation resulted in a strategic shift in how the Company viewed its natural gas compressor manufacturing business, operated by its then-subsidiary, Clean Energy Compression Corp. (“CEC”). In an effort to increase the scale and reach and improve the financial prospects of the Company’s investment in this business, the Company entered into an investment agreement with a strategic partner in November 2017, pursuant to which both parties combined their respective natural gas compressor manufacturing businesses (see Note 5 for more information). As a result of these decisions and the steps taken to implement them, the Company incurred, during the three months ended September 30, 2017 and on a pre-tax basis, aggregate cash and non-cash charges related to asset impairments and other charges, and a non-cash inventory valuation charge.

The following table summarizes these charges:



	Three and Nine Months Ended September 30, 2017
Workforce reduction and related charges	$	3,057
CEC asset impairments	32,274
Station closures and related charges	25,335
Total asset impairments and other charges	$	60,666
Inventory valuation provision	13,158
Total charges	$	73,824

Cash Charges

The following table summarizes the charges related to the foregoing that have been or will be settled with cash payments and their related liability balances as of December 31, 2017 and September 30, 2018, respectively:



	Charges		Cash Payments Made as of December 31, 2017		Balance as of December 31, 2017		Cash Payments Made as of September 30, 2018			Balance as of September 30, 2018
Employee severance	$	2,757	(2,757	)	$	—	$	—		$	—
Lease termination fees and AROs for station closures	3,861		(70	)	3,791		(1,667		)	2,124
	$	6,618	(2,827	)	$	3,791	(1,667		)	$	2,124

Divestitures	9 Months Ended
Divestitures	Sep. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Divestitures	Divestitures On February 27, 2017, Clean Energy Renewable Fuels (“Renewables”), a subsidiary of the Company, entered into an asset purchase agreement (the “APA”) with BP Products North America, Inc. (“BP”). Pursuant to the APA, Renewables agreed to sell to BP its assets relating to its RNG production business (the “BP Transaction”), consisting of Renewables’ two RNG production facilities, Renewables’ interest in joint ventures formed with a third party to develop new RNG production facilities, and Renewables’ third-party RNG supply contracts (the “Assets”). The BP Transaction was completed on March 31, 2017 for a sale price of $155,511, plus BP assumed all $8,820 of remaining obligations under the Canton Bonds (as defined in Note 13). On March 31, 2017, BP paid Renewables $30,000 in cash and delivered to Renewables a promissory note with a principal amount of $123,487, which was paid in full on April 3, 2017. In addition, as a result of the determination of certain post-closing adjustments, (i) BP paid Renewables an additional $2,010 on June 22, 2017, and (ii) the gain recorded from the BP Transaction was reduced by $762. Pursuant to the APA, the valuation date of the BP Transaction was January 1, 2017, and as a result, the APA included certain adjustments to the purchase price to reflect a determination of the amount of cash accumulated by Renewables from the valuation date to the closing date, net of permitted cash outflows. Control of the Assets was not transferred until the BP Transaction was completed on March 31, 2017. Accordingly, the full operating results of Renewables are included in the accompanying condensed consolidated statements of operations through the March 31, 2017 closing date. In addition, under the APA, BP is required, following the closing of the BP Transaction, to pay Renewables up to an additional $25,000 in cash over a five-year period if certain performance criteria relating to the Assets are met. The Company satisfied the performance criteria for the first such period, which ended on December 31, 2017, and as a result, the Company recognized a net gain of $772 as of December 31, 2017, which is included in the total gain on the BP Transaction. The Company incurred $3,695 in transaction fees in connection with the BP Transaction, and the Company paid $8,605 in cash and issued 770,269 shares of the Company’s common stock with a fair value of $1,964 to former holders of options to purchase membership units in Renewables. The net proceeds from the BP Transaction were $142,190, net of $1,007 cash transferred to BP. In February 2018, the Company received $871 in cash for its satisfaction of the performance criteria for the first period under the APA. Upon its receipt of such cash, the Company paid $65 in cash and issued 15,877 shares of the Company’s common stock with a fair value of $34 to former holders of options to purchase membership units in Renewables. Following the completion of the BP Transaction, Renewables and the Company continue to procure RNG from BP under a long-term supply contract and from other RNG suppliers, and resell such RNG through the Company’s natural gas fueling infrastructure as Redeem, the Company’s RNG vehicle fuel. The Company also collects royalties from BP on gas purchased from BP and sold as Redeem at the Company’s fueling stations. The BP Transaction resulted in a total gain of $69,886 as of December 31, 2017. Included in the total gain is goodwill of $26,576 allocated to the disposed assets based on the relative fair values of the assets disposed and the portion of the retained reporting unit. The Company determined that the BP Transaction did not meet the definition of a discontinued operation because the disposal did not represent a strategic shift that will have a major effect on the Company’s operations and financial results.

Investments in Other Entities and Noncontrolling Interest in a Subsidiary	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Investments in Other Entities and Noncontrolling Interest in a Subsidiary	Investments in Other Entities and Noncontrolling Interest in a Subsidiary SAFE&CEC S.r.l. On November 26, 2017, the Company, through its former subsidiary, CEC, entered into an investment agreement with Landi Renzo S.p.A. (“LR”), an alternative fuels company based in Italy. Pursuant to the investment agreement, the Company and LR agreed to combine their respective natural gas compressor subsidiaries, CEC and SAFE S.p.A, in a new company known as “SAFE&CEC S.r.l.” (such combination transaction is referred to as the “CEC Combination”). SAFE&CEC S.r.l. is focused on manufacturing, selling and servicing natural gas fueling compressors and related equipment for the global natural gas fueling market. Upon the closing of the CEC Combination on December 29, 2017, the Company owns 49% of SAFE&CEC S.r.l. and LR owns 51% of SAFE&CEC S.r.l. The Company accounts for its interest in SAFE&CEC S.r.l. using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over SAFE&CEC S.r.l.’s operations. The Company recorded a loss from this investment of $817 and $2,964 for the three and nine months ended September 30, 2018, respectively. Subsequent to December 29, 2017, the Company recorded an increase of $1,163 in anticipated relocation expenses under the investment agreement in “Accrued liabilities” in the accompanying condensed consolidated balance sheet as of September 30, 2018 and in “Loss from formation of equity method investment” in the accompanying condensed consolidated statement of operations for the nine months ended September 30, 2018. The Company has an investment balance in SAFE&CEC S.r.l. of $27,883 and $24,936 as of December 31, 2017 and September 30, 2018, respectively. The Company determined that the CEC Combination did not meet the definition of a discontinued operation because the disposal did not represent a strategic shift that will have a major effect on the Company’s operations and financial results. MCEP On September 16, 2014, the Company formed a joint venture with Mansfield Ventures LLC (“Mansfield Ventures”) called Mansfield Clean Energy Partners LLC (“MCEP”), which is designed to provide natural gas fueling solutions to bulk fuel haulers in the United States. The Company and Mansfield Ventures each have a 50% ownership interest in MCEP. The Company accounts for its interest in MCEP using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over MCEP’s operations. The Company recorded a gain (loss) from this investment of $(30) and $276 for the three months ended September 30, 2017 and 2018, respectively, and $(100) and $226 for the nine months ended September 30, 2017 and 2018, respectively. The Company has an investment balance in MCEP of $1,512 and $1,738 as of December 31, 2017 and September 30, 2018, respectively. NG Advantage On October 14, 2014, the Company entered into a Common Unit Purchase Agreement (“UPA”) with NG Advantage for a 53.3% controlling interest in NG Advantage. NG Advantage is engaged in the business of transporting CNG in high-capacity trailers to industrial and institutional energy users, such as hospitals, food processors, manufacturers and paper mills that 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. The results of NG Advantage’s operations have been included in the Company’s consolidated financial statements since October 14, 2014. On July 14, 2017, the Company contributed to NG Advantage all of its right, title and interest in and to a CNG fueling station located in Milton, Vermont. The Company purchased this CNG fueling station from NG Advantage in October 2014 in connection with the UPA, and at that time, the Company entered into a lease agreement with NG Advantage to lease the station back to NG Advantage. This lease agreement was terminated contemporaneously with the contribution of the station to NG Advantage in July 2017. As consideration for the contribution, NG Advantage issued to the Company Series A Preferred Units with an aggregate value of $7,500. The Series A Preferred Units provide for an accrued return upon a liquidation event with respect to NG Advantage and will convert into common units of NG Advantage if and when it completes a future equity financing that satisfies certain specified conditions; however, the Series A Preferred Units do not, in themselves, increase the Company’s controlling interest in NG Advantage. As a result, immediately following the contribution, the Company’s controlling interest in NG Advantage remained at 53.3%. On February 28, 2018, the Company entered into a guaranty agreement with NG Advantage and BP for the purchase, sale and transportation of CNG. The Company guarantees NG Advantage’s payment obligations in the event of default up to $30,000 plus related fees. This guaranty is in effect until thirty days following the Company’s notice to NG Advantage’s customer of its termination. As consideration for the guaranty agreement, NG Advantage issued to the Company 19,660 common units, which increased the Company’s controlling interest in NG Advantage from 53.3% to 53.5%. On October 1, 2018, the Company purchased 1,000,001 common units from NG Advantage for an aggregate cash purchase price of $5,000. This purchase increased Clean Energy's controlling interest in NG Advantage from 53.3% to 61.7% as of October 1, 2018. Net loss included a loss from the noncontrolling interest in NG Advantage of $747 and $1,300 for the three months ended September 30, 2017 and 2018, respectively, and $1,813 and $4,235 for the nine months ended September 30, 2017 and 2018, respectively. The value of the noncontrolling interest was $22,668 and $18,433 as of December 31, 2017 and September 30, 2018, respectively.

Cash, Cash Equivalents, and Restricted Cash

9 Months Ended

Sep. 30, 2018

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents, and Restricted Cash

Cash, cash equivalents and restricted cash as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Cash and cash equivalents	$	36,081	$	158,143
Restricted cash - standby letters of credit	1,127		1,127
Restricted cash - held in escrow	—		750
Total cash, cash equivalents and restricted cash	$	37,208	$	160,020

The Company considers all highly liquid investments with maturities of three months or less on the date of acquisition to be cash equivalents. 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”) and Canadian Deposit Insurance Corporation (“CDIC”). Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash deposits. The amounts in excess of FDIC and CDIC limits were approximately $34,709 and $156,795 as of December 31, 2017 and September 30, 2018, respectively.

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. Short-term restricted cash consisted of standby letters of credit renewed annually and an amount held in escrow. As of December 31, 2017 and September 30, 2018, the Company had no long-term restricted cash.

Short-term Investments

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Short-term Investments

Short-term investments include available-for-sale debt securities and certificates of deposit. Available-for-sale debt securities are carried at fair value, inclusive of unrealized gains and losses. Unrealized gains and losses for debt securities are recognized in other comprehensive income, net of applicable income taxes. Gains or losses on sales of available-for-sale debt securities are recognized on the specific identification basis.

The Company reviews available-for-sale debt securities 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 September 30, 2018, the Company believes its carrying values for its available-for-sale debt securities are properly recorded.

Short-term investments as of December 31, 2017 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	21,414	$	(49	)	$	21,365
Zero coupon bonds	54,159		(33		)	54,126
Corporate bonds	55,109		(40		)	55,069
Certificates of deposit	10,902		—			10,902
Total short-term investments	$	141,584	$	(122	)	$	141,462

Short-term investments as of September 30, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	16,351	$	—		$	16,351
Zero coupon bonds	64,871		(2		)	64,869
Corporate bonds	3,721		2			3,723
Certificates of deposit	11,021		—			11,021
Total short-term investments	$	95,964	$	—		$	95,964

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

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 non-recurring 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.

Assets and Liabilities Measured at Fair Value on a Recurring Basis

The Company’s available-for-sale debt securities and certificate of deposits are classified within Level 2 because they are valued using the most recent quoted prices for identical assets in markets that are not active and quoted prices for similar assets in active markets. The Company’s liability-classified warrants are classified within Level 3 because the Company uses the Black-Scholes option pricing model to estimate the fair value based on inputs that are not observable in any market. There were no transfers of assets between Level 1, Level 2, or Level 3 of the fair value hierarchy as of December 31, 2017 or September 30, 2018.

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, 2017 and September 30, 2018, respectively:



Description	Balance at December 31, 2017		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	21,365	$	—	$	21,365	$	—
Zero coupon bonds	54,126		—		54,126		—
Corporate bonds	55,069		—		55,069		—
Certificates of deposit ⁽¹⁾	10,902		—		10,902		—
Liabilities:
Warrants ⁽²⁾	$	536	$	—	$	—	$	536



Description	Balance at September 30, 2018		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	16,351	$	—	$	16,351	$	—
Zero coupon bonds	64,869		—		64,869		—
Corporate bonds	3,723		—		3,723		—
Certificates of deposit ⁽¹⁾	11,021		—		11,021		—
Liabilities:
Warrants ⁽²⁾	$	435	$	—	$	—	$	435

(1) Included in Short-term investments in the accompanying condensed consolidated balance sheets. See Note 7 for more information.

(2) Included in Accrued liabilities and Other long-term liabilities in the accompanying condensed consolidated balance sheets.

Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis

During the three and nine months ended September 30, 2017, long-lived assets held and used with a carrying value of $59,367 were written down to their fair value of $6,709, resulting in charges of $52,658. The fair value of these assets was determined using Level 3 inputs. See Note 3 for more information.

Other Financial Assets and Liabilities

The carrying amounts of the Company’s cash, cash equivalents and restricted cash, receivables and payables approximate fair value due to the short-term nature of those instruments. The carrying amounts of the Company’s debt instruments approximated their respective fair values as of December 31, 2017 and September 30, 2018. The fair values of these debt instruments were estimated using a discounted cash flow analysis based on interest rates offered on loans with similar terms to borrowers of similar credit quality, which are Level 3 inputs. See Note 13 for more information about the Company’s debt instruments.

- 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

Other Receivables

9 Months Ended

Sep. 30, 2018

Receivables [Abstract]

Other Receivables

Other receivables as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Loans to customers to finance vehicle purchases	$	4,746	$	5,360
Accrued customer billings	10,072		9,007
Fuel tax credits	177		1,256
Other	4,240		2,267
Total other receivables	$	19,235	$	17,890

- 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

Inventory

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Inventory

Inventory consists of raw materials and spare parts, work in process and finished goods and is stated at the lower of cost (first-in, first-out) or net realizable value. The Company evaluates inventory balances for excess quantities and obsolescence by analyzing estimated demand, inventory on hand, sales levels and other information and reduces inventory balances to net realizable value for excess and obsolete inventory based on this analysis.

Inventories as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Raw materials and spare parts	$	35,145	$	37,013
Finished goods	93		90
Total inventories	$	35,238	$	37,103

Land, Property and Equipment

9 Months Ended

Sep. 30, 2018

Property, Plant and Equipment [Abstract]

Land, Property and Equipment

Land, property and equipment as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017			September 30, 2018
Land	$	2,858		$	2,858
LNG liquefaction plants	94,634			94,634
Station equipment	304,090			307,301
Trailers	70,906			71,284
Other equipment	88,313			95,623
Construction in progress	74,905			74,501
	635,706			646,201
Less: accumulated depreciation	(268,401		)	(302,124		)
Total land, property and equipment, net	$	367,305		$	344,077

Included in Land, property and equipment are capitalized software costs of $26,003 and $28,910 as of December 31, 2017 and September 30, 2018, respectively. Accumulated amortization of the capitalized software costs is $18,737 and $21,424 as of December 31, 2017 and September 30, 2018, respectively.

The Company recorded amortization expense related to the capitalized software costs of $1,140 and $1,026 for the three months ended September 30, 2017 and 2018, respectively, and $3,134 and $2,699 for the nine months ended September 30, 2017 and 2018, respectively.

As of September 30, 2017 and 2018, $2,007 and $1,660, respectively, are included in accounts payable and accrued liabilities balances, which amounts are related to purchases of property and equipment. These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.

Accrued Liabilities

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Accrued Liabilities

Accrued liabilities as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Accrued alternative fuels incentives ⁽¹⁾	$	2,954	$	5,900
Accrued employee benefits	2,378		3,381
Accrued interest	1,486		4,897
Accrued gas and equipment purchases	8,722		10,560
Accrued property and other taxes	4,582		4,245
Accrued salaries and wages	8,363		6,117
Other ⁽²⁾	13,783		13,222
Total accrued liabilities	$	42,268	$	48,322


(1)	Includes the amount of RINs and LCFS Credits and, as of September 30, 2018, the amount of AFTC payable to third parties. The AFTC expired as of December 31, 2017, but was reinstated in February 2018 for vehicle fuel sales made from January 1, 2017 through December 31, 2017. See Note 19 for more information about AFTC.

(2)

The amount as of December 31, 2017 and September 30, 2018 includes lease termination fees and asset retirement obligations related to the closure of certain fueling stations and working capital adjustments in the third and fourth quarters of 2017 (see Note 3 for more information), in addition to funding for certain commitments and transaction fees incurred as a result of the CEC Combination (see Note 5 for more information).

Debt

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Debt

Debt and capital lease obligations as of December 31, 2017 and September 30, 2018 consisted of the following and are further discussed below:



	December 31, 2017
	Principal Balances			Unamortized Debt Financing Costs			Balance, Net of Financing Costs
7.5% Notes	$	125,000		$	131		$	124,869
5.25% Notes	110,450			454			109,996
NG Advantage debt and capital lease obligations	23,437			259			23,178
Capital lease obligations	802			—			802
Other debt	1,242			—			1,242
Total debt and capital lease obligations	260,931			844			260,087
Less amounts due within one year	(140,223		)	(524		)	(139,699		)
Total long-term debt and capital lease obligations	$	120,708		$	320		$	120,388



	September 30, 2018
	Principal Balances			Unamortized Debt Financing Costs			Balance Net of Financing Costs
7.5% Notes	$	100,000		$	72		$	99,928
5.25% Notes	110,450			2			110,448
NG Advantage debt and capital lease obligations	26,723			292			26,431
Capital lease obligations	809			—			809
Other debt	1,080			—			1,080
Total debt and capital lease obligations	239,062			366			238,696
Less amounts due within one year	(115,951		)	(72		)	(115,879		)
Total long-term debt and capital lease obligations	$	123,111		$	294		$	122,817

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 pursuant to the issuance of three convertible promissory notes over a three-year period, 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”), T. Boone Pickens and Green Energy Investment Holdings, LLC (“GEIH”), 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 is also a party to 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 new holders 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 “2013 Advance”). In addition, the Company canceled the existing CHK Notes and issued replacement notes, and the Company also issued notes to the Buyers in exchange for the 2013 Advance (the replacement notes and the notes issued in exchange for the 2013 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 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, each holder of a 7.5% Note has the right to exchange all or any portion of the principal and accrued and unpaid interest under its 7.5% Notes 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 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 original issuance and the Company may repay each 7.5% Note at maturity in shares of its common stock (provided that the Company may not issue more than 13,993,630 shares of its common stock to holders of 7.5% Notes) or cash. All of the shares issuable upon conversion 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 SEC.

The Amended 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 7.5% Notes to become, or to be declared, due and payable. No events of default under the 7.5% Notes had occurred as of September 30, 2018.

On August 27, 2013, GEIH transferred $5,000 in principal amount of its 7.5% Notes to certain third parties.

On February 9, 2017, the Company purchased from Mr. Pickens, his 7.5% Note due July 2018 having an outstanding principal amount of $25,000 for a cash purchase price of $21,750. Upon such purchase, the applicable 7.5% Notes were surrendered and canceled in full. The Company’s repurchase of this 7.5% Note resulted in a gain of $3,191 for the nine months ended September 30, 2017.

On February 21, 2017, GEIH transferred $11,800 in principal amount of its 7.5% Notes to certain third parties.

On November 17, 2017, Mr. Pickens transferred all remaining $40,000 in principal amount of his 7.5% Notes to a third party.

On June 29, 2018, and pursuant to the consent of the holders of the 7.5% Notes to the Company’s payments of amounts owed thereunder before maturity, the Company paid to the holders, in cash, an aggregate of $25,000 in principal amount and $505 in accrued and unpaid interest owed under all outstanding 7.5% Notes due July 2018. Upon such payment, the applicable 7.5% Notes were surrendered and canceled in full.

As a result of the foregoing transactions, as of September 30, 2018, (i) GEIH held 7.5% Notes in an aggregate principal amount of $56,435, and (ii) other third parties held 7.5% Notes in an aggregate principal amount of $43,565.

5.25% Notes

In September 2013, the Company completed a private offering of $250,000 in principal amount 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 used the net proceeds from the sale of the 5.25% Notes to fund capital expenditures and for general corporate purposes. The 5.25% Notes bore 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 matured October 1, 2018, unless any such notes were purchased, redeemed or converted prior to such date in accordance with their terms and the terms of the Indenture.

The Indenture contained customary events of default with customary cure periods, including, without limitation, failure to make required payments or deliveries of shares of the Company’s 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 would 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, would automatically cause the acceleration of, all amounts due under the 5.25% Notes. No events of default under the 5.25% Notes had occurred as of September 30, 2018.

Prior to September 30, 2018, the Company (i) paid an aggregate of $84,344 in cash to repurchase $114,550 in aggregate principal amount of the 5.25% Notes and (ii) issued an aggregate of 6,265,829 shares of its common stock in exchange for an aggregate of $25,000 in aggregate principal amount of the 5.25% Notes, together with all accrued and unpaid interest thereon. No such repurchases or exchanges occurred during the nine months ended September 30, 2017 or 2018. All repurchased and exchanged 5.25% Notes have been surrendered to the trustee for such notes and canceled in full and the Company has no further obligations under such notes.

On October 1, 2018, the Company paid to the holders, in cash, an aggregate of $110,450 in principal amount and $2,899 in accrued and unpaid interest owed under all then-outstanding 5.25% Notes due October 2018. Upon such payment, the 5.25% Notes were surrendered and canceled in full and the Company has no further obligations under such notes.

Plains Credit Facility

On February 29, 2016, the Company entered into a Loan and Security Agreement (the “Plains LSA”) with PlainsCapital Bank (“Plains”), which, as amended on December 6, 2017, has a maturity date of September 30, 2019. Pursuant to the Plains LSA, Plains agreed to lend the Company up to $50,000 on a revolving basis from time to time (the “Credit Facility”). Simultaneously, the Company drew $50,000 under this Credit Facility, which the Company repaid in full on August 31, 2016. On December 22, 2016, the Company drew $23,500 under the Credit Facility, which the Company repaid in full on March 31, 2017. As a result, the Company had no amounts outstanding under the Credit Facility as of September 30, 2018.

The Credit Facility is evidenced by a promissory note issued by the Company on February 29, 2016 in favor of Plains (the “Plains Note”). Interest on the Plains Note is payable monthly and accrues at a rate equal to the greater of (i) the then-current LIBOR rate plus 2.30% or (ii) 2.70%. As collateral security for the prompt payment in full when due of the Company’s obligations to Plains under the Plains LSA and the Plains Note, the Company pledged to and granted Plains a security interest in all of its right, title and interest in the cash and corporate and municipal bonds rated AAA, AA or A by Standard & Poor’s Rating Services that the Company holds in an account at Plains. In connection with such pledge and security interest granted under the Credit Facility, on February 29, 2016, the Company entered into a Pledged Account Agreement with Plains and PlainsCapital Bank - Wealth Management and Trust (the “Pledge Agreement” and collectively with the Plains LSA and the Plains Note, the “Plains Loan Documents”).The Plains Loan Documents include certain covenants of the Company and also provide for customary events of default, which, if any of them occurs, would permit or require, among other things, the principal of, and accrued interest on, the Credit Facility to become, or to be declared, due and payable. Events of default under the Plains Loan Documents include, among others, the occurrence of certain bankruptcy events, the failure to make payments when due under the Plains Note and the transfer or disposal of the collateral under the Plains LSA. No events of default under the Plains Loan Documents had occurred as of September 30, 2018.

Canton Bonds

On March 19, 2014, Canton Renewables, LLC (“Canton”), a former 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 “Canton Bonds”). The Canton 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. On March 31, 2017, Canton was sold to BP in the BP Transaction (see Note 4). As a result, the Canton Bonds became the obligation of BP as of such date.

NG Advantage Debt and Capital Lease Obligations

NG Advantage has debt and capital lease obligations for trailers and equipment due at various dates through 2025 bearing interest at rates up to 8.76%, with weighted -average interest rates of 4.98% and 5.89% as of December 31, 2017 and September 30, 2018, respectively. NG Advantage pledged to and granted a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received from various creditors.

Other Debt

The Company has other debt due at various dates through 2023 bearing interest at rates up to 5.02%, with weighted -average interest rates of 4.79% and 4.79% as of December 31, 2017 and September 30, 2018, respectively.

Net Loss Per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

Basic net loss per share is computed by dividing the 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 the 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 and potentially dilutive securities outstanding during the period, and therefore reflects the dilution from common shares that may be issued upon exercise or conversion of these potentially dilutive securities, such as stock options, warrants, convertible notes and restricted stock units. The dilutive effect of stock awards 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.

The information required to compute basic and diluted net loss per share is as follows:



	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2018	2017	2018
Weighted-average common shares outstanding	150,927,825	203,469,222	150,128,204	172,946,896
Dilutive effect of potential common shares from restricted stock units and stock options	—	—	—	—
Weighted-average common shares outstanding -diluted	150,927,825	203,469,222	150,128,204	172,946,896

The following potentially dilutive securities have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive. Although these securities were antidilutive for these periods, they could be dilutive in future periods.



	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2018	2017	2018
Stock Options	9,648,613	9,417,492	9,648,613	9,417,492
Convertible Notes	14,991,521	13,409,242	14,991,521	13,409,242
Restricted Stock Units	2,403,266	2,428,731	2,403,266	2,428,731
Total	27,043,400	25,255,465	27,043,400	25,255,465

At-The-Market Offering Program

On May 31, 2017, the Company terminated its equity distribution agreement (the “Sales Agreement”) with Citigroup Global Markets Inc. (“Citigroup”), as sales agent and/or principal. The Sales Agreement was terminable at will upon written notification by the Company with no penalty. Pursuant to the Sales Agreement, the Company was entitled to issue and sell, from time to time through or to Citigroup, shares of its common stock having an aggregate offering price of up to $200,000 in an “at-the-market” offering program (the “ATM Program”). The ATM Program commenced on November 11, 2015 when the Company and Citigroup entered into the original equity distribution agreement, which was amended and restated on September 9, 2016 and again on December 21, 2016 prior to its termination.

The following table summarizes the activity under the ATM Program for the periods presented:



	Nine Months Ended September 30, 2017
Gross proceeds	$	10,767
Fees and issuance costs	311
Net proceeds	$	10,456
Shares issued	3,802,500

Stock-Based Compensation

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

The following table summarizes the compensation expense and related income tax benefit related to the Company’s stock-based compensation arrangements recognized in the accompanying condensed consolidated statements of operations during the periods:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2018		2017		2018
Stock-based compensation expense, net of $0 tax in 2017 and 2018 ⁽¹⁾	$	2,216	$	1,206	$	6,904	$	4,312

(1) $300 of stock-based compensation expense for the three and nine months ended September 30, 2017 is recorded in asset impairments and other charges in the accompanying condensed consolidated statements of operations and is reported in asset impairments and other charges in the accompanying condensed consolidated statements of cash flows. See Note 3 for more information.

As of September 30, 2018, there was $5,242 of total unrecognized compensation costs related to unvested shares subject to outstanding stock options and restricted stock units, which is expected to be expensed over a weighted-average period of approximately 1.84 years.

Stockholders’ Equity	9 Months Ended
Stockholders’ Equity	Sep. 30, 2018
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Issuance of Common Stock On May 9, 2018, the Company entered into a stock purchase agreement (the “Purchase Agreement”) with Total Marketing Services, S.A., a wholly owned subsidiary of Total S.A. (“Total”). Pursuant to the Purchase Agreement, the Company agreed to sell and issue, and Total agreed to purchase, up to 50,856,296 shares of the Company’s common stock at a purchase price of $1.64 per share, all in a private placement (the “Total Private Placement”). The purchase price per share was determined based on the volume-weighted average price for the Company’s common stock between March 23, 2018 (the day on which discussions began between the Company and Total) and May 3, 2018 (the day on which the Company agreed in principle with Total regarding the structure and basic terms of its investment). As of the date of the Purchase Agreement, Total did not hold or otherwise beneficially own any shares of the Company’s common stock, and Total has agreed, until the later of May 9, 2020 or such date when it ceases to hold more than 5.0% of the Company’s common stock then outstanding, among other similar undertakings and subject to customary conditions and exceptions, to not purchase shares of the Company’s common stock or otherwise pursue transactions that would result in Total beneficially owning more than 30.0% of the Company’s equity securities without the approval of the Company’s board of directors. On June 13, 2018, the Company and Total closed the Total Private Placement, in which: (1) the Company issued to Total all of the 50,856,296 shares of its common stock issuable under the Purchase Agreement, resulting in Total holding approximately 25.0% of the outstanding shares of the Company’s common stock and the largest ownership position of the Company as of September 30, 2018; (2) Total paid to the Company an aggregate of $83,404 in gross proceeds, which the Company has used and expects to continue to use for working capital and general corporate purposes, which may include executing its business plans, pursuing opportunities for further growth, and retiring a portion of its outstanding indebtedness; and (3) the Company and Total entered into a registration rights agreement, described below. In connection with the issuance of common stock, the Company incurred transaction fees of $2,694. Pursuant to the Purchase Agreement, the Company and Total also entered into a registration rights agreement on June 13, 2018, upon the closing under the Purchase Agreement. Pursuant to the registration rights agreement, the Company filed a registration statement with the SEC to cover the resale of the shares issued and sold under the Purchase Agreement, which was declared effective on August 16, 2018, and is obligated to use its commercially reasonable efforts to maintain the effectiveness of such registration statement until all such shares are sold or may be sold without restriction under Rule 144 under the Securities Act of 1933, as amended. As of September 30, 2018, the Company was in compliance with all of its registration covenants set forth in the registration rights agreement. During the nine months ended September 30, 2017, we issued and sold 3,802,500 shares of our common stock for gross proceeds of $10,767 in the ATM Program. See Note 14 for more information.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for interim periods is determined using an estimate of the Company’s annual effective tax rate, adjusted for discrete items, if any, that are taken into account in the relevant period. Each quarter, the Company updates the estimate of the annual effective tax rate, and if the estimated tax rate changes, a cumulative adjustment is recorded. The Company’s income tax benefit (expense) was $44 and $(89) for the three months ended September 30, 2017 and 2018, respectively, and $2,183 and $(266) for the nine months ended September 30, 2017 and 2018, respectively. Tax benefit (expense) for the 2018 periods was comprised of taxes due on the Company's U.S. operations, and for the 2017 periods was comprised of taxes due on the Company’s U.S. and foreign operations. The decrease in the Company’s income tax benefit for the three months ended September 30, 2018 as compared to the three months ended September 30, 2017 was primarily due to the absence of the tax benefit that arose from the Company's foreign operations following the CEC Combination (see Note 5). The decrease in the Company’s income tax benefit for the nine months ended September 30, 2018 as compared to the nine months ended September 30, 2017 was primarily due to a decrease in the deferred tax benefit attributed to the reduction of goodwill amortization following the BP Transaction (see Note 4). The effective tax rates for the three and nine months ended September 30, 2017 and 2018 are different from the federal statutory tax rate primarily due to losses for which no tax benefit has been recognized. Following the BP Transaction and during the year ended December 31, 2017, the Company also benefited from the utilization of federal and state net operating loss (“NOL”) carryovers that offset all of the Company's federal and the majority of its state taxes. In addition to the decrease in its deferred tax liability of $2,493 attributed to the reduction in goodwill following the BP Transaction, the utilization of NOLs also resulted in a decrease of $29,768 in the Company’s deferred tax assets attributed to NOLs and a corresponding decrease in the Company's deferred tax asset valuation allowance. The Company increased its liability for unrecognized tax benefits in the nine months ended September 30, 2018 by $2,178, which was primarily attributable to the portion of AFTC revenue recognized in the period that was offset by the fuel tax the Company collected from its customers as an unrecognized tax benefit during the year ended December 31, 2017. The net interest incurred was immaterial for both the three and nine months ended September 30, 2017 and 2018, respectively.

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 that 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. The Company is also subject to audit by tax and other authorities for varying periods in various federal, state, local and foreign jurisdictions, and disputes may arise during the course of these audits. It is impossible to determine the ultimate liabilities that the Company may incur resulting from any of these lawsuits, claims, proceedings, audits, commitments, contingencies and related matters or the timing of these liabilities, if any. If these matters were to ultimately be resolved unfavorably, it is possible that such an outcome could have a material adverse effect upon the Company’s consolidated financial position, results of operations, or liquidity. The Company, does not, however, anticipate such an outcome and it believes the ultimate resolution of these matters will not have a material adverse effect on the Company’s consolidated financial position, results of operations, or liquidity.

Alternative Fuels Excise Tax Credit	9 Months Ended
Alternative Fuels Excise Tax Credit	Sep. 30, 2018
Alternative Fuels Excise Tax Credit
Alternative Fuels Excise Tax Credit	Alternative Fuels Excise Tax Credit Under separate pieces of U.S. federal legislation, the Company has been eligible to receive the AFTC tax credit for its natural gas vehicle fuel sales made between October 1, 2006 and December 31, 2017. The AFTC, which had previously expired on December 31, 2016, was reinstated on February 9, 2018 to apply to vehicle fuel sales made from January 1, 2017 through December 31, 2017. The AFTC credit is equal to $0.50 per gasoline gallon equivalent of CNG that the Company sold as vehicle fuel, $0.50 per liquid gallon of LNG that the Company sold as vehicle fuel through 2015, and $0.50 per diesel gallon of LNG that the Company sold as vehicle fuel in 2016 and 2017. Based on the service relationship with its customers, either the Company or its customers claims the credit. The Company records its AFTC credits, if any, as revenue in its consolidated statements of operations because the credits are fully payable to the Company and do not offset income tax liabilities. As such, the credits are not deemed income tax credits under the accounting guidance applicable to income taxes. As a result of the most recent legislation authorizing AFTC being signed into law on February 9, 2018, all AFTC revenue for vehicle fuel the Company sold in the 2017 calendar year, totaling $25,481, has been recognized and collected during the nine months ended September 30, 2018. In addition, during the nine months ended September 30, 2018, the Internal Revenue Service approved, and the Company recognized as revenue, $1,382 of AFTC credit claims related to prior years. AFTC is not currently available, and may not be reinstated, for vehicle fuel sales made after December 31, 2017.

Recently Adopted Accounting Changes and Recently Issued Accounting Standards

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Recently Adopted Accounting Changes and Recently Issued Accounting Standards

Recently Adopted Accounting Changes

In February 2018, the Financial Accounting Standards Board (“FASB”) issued ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows for a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act (the “TCJA”). This update is effective for fiscal years beginning after December 15, 2018, which for the Company is the first quarter of 2019, with early adoption permitted. The Company elected to early adopt this ASU during the nine months ended September 30, 2018, which did not have any impact on the accompanying condensed consolidated financial statements or related disclosures. The Company did not elect to reclassify the stranded tax effects of the TCJA as there were none.

In December 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The new standard requires restricted cash and restricted cash equivalents to be included as components of total cash and cash equivalents as presented on the statement of cash flows. This pronouncement is effective for reporting periods beginning after December 15, 2017, which for the Company is the first quarter of 2018. The Company adopted this standard on a retrospective basis, and adoption did not have a material impact on the Company’s consolidated financial statements or related disclosures. As a result of including restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts presented in the accompanying condensed consolidated statement of cash flows, net cash flows decreased by $5,533 for the nine months ended September 30, 2017 (see Note 1).

In September 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Payments. The new standard provides clarification as to the classification of certain transactions as operating, investing or financing activities. This pronouncement is effective for reporting periods beginning after December 15, 2017, which for the Company is the first quarter of 2018. Adoption of this standard did not have any impact on the accompanying condensed consolidated financial statements and related disclosures for the nine months ended September 30, 2018.

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASC 606”), which amends the guidance in former Accounting Standards Codification Topic 605, Revenue Recognition, to provide a single, comprehensive revenue recognition model for all contracts with customers. The new standard requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in amounts that reflect the consideration to which an entity expects to be entitled in exchange for those goods or services. The new standard also requires entities to enhance disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The standard is effective for fiscal years beginning after December 15, 2017, which for the Company was the first quarter of 2018.

The Company adopted this standard using the modified retrospective method and recognized the cumulative effect of initially applying ASC 606 as an adjustment to accumulated deficit in the consolidated balance sheet as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under ASC 606, while prior period amounts are not adjusted. This adoption did not have a material impact to the Company’s condensed consolidated financial statements.

The ASC 606 adoption adjustments are as follows, and relate to significant financing components resulting from an advance payment by a customer of NG Advantage and an extended payment term to a station construction customer:



	Balance as of December 31, 2017			Adjustments Due to ASC 606			Balance as of January 1, 2018
Notes receivable and other long-term assets, net	$	21,397		$	(963	)	$	20,434
Deferred revenue	$	3,432		$	330		$	3,762
Accumulated deficit	$	(683,570	)	$	(1,293	)	$	(684,863	)

The ASC 606 adoption adjustments on the accompanying condensed consolidated balance sheet as of September 30, 2018 are as follows:



	September 30, 2018
	Balance before ASC 606 Adoption			Effect of Change			As Reported
Notes receivable and other long-term assets, net	$	16,885		$	(907	)	$	15,978
Deferred revenue	$	7,989		$	841		$	8,830
Accumulated deficit	$	(693,767	)	$	(1,748	)	$	(695,515	)

The impact on the accompanying condensed consolidated statements of operations for the three and nine months ended September 30, 2018 was immaterial.

Recently Issued Accounting Standards

In February 2016, the FASB issued ASU 2016-02, Leases. The new standard requires most leases to be recognized on the balance sheet which will increase reported assets and liabilities. Lessor accounting remains substantially similar to current guidance. The new standard is effective for annual and interim periods in fiscal years beginning after December 15, 2018, which for the Company is the first quarter of 2019, and mandates adoption using a modified retrospective method. The Company has completed its first phase of globally identifying its leases and is in the process of identifying changes to its processes, internal controls and system requirements and configurations that would result from the new lease standard. The Company’s implementation efforts are progressing as planned. The Company’s evaluation of the impact this ASU will have on its consolidated financial statements and related disclosures is ongoing and not complete.

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In October 2018, in support of the Company’s truck financing program, which the Company calls “Zero Now Financing,” the Company executed two commodity swap contracts with Total Gas & Power North America, an affiliate of Total, for a total of five million diesel gallons annually from April 1, 2019 to June 30, 2024. These commodity swap contracts are used to manage the risk related to the diesel -to -natural gas price spread and are measured at fair value with changes in the fair value to be recorded in the consolidated statement of operations in the period incurred.

General (Policies)

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of Presentation

The accompanying interim unaudited condensed 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 consolidated financial position as of September 30, 2018, and results of operations and comprehensive loss for the three and nine months ended September 30, 2017 and 2018, and cash flows for the nine months ended September 30, 2017 and 2018. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and nine month periods ended September 30, 2017 and 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other interim period or for any future year.

Certain information and disclosures normally included in the notes to consolidated financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”), but the resultant disclosures contained herein are in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) as they apply to interim reporting. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2017 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 13, 2018.

Reclassifications

During the nine months ended September 30, 2018, the Company adopted Accounting Standards Update (“ASU”) No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (see Note 20). The new standard requires restricted cash and restricted cash equivalents to be included as components of total cash and cash equivalents as presented on the statement of cash flows. As a result, the Company chose to also conform this classification on the accompanying condensed consolidated balance sheets. This resulted in prior period restricted cash of $1,127 as of December 31, 2017 being reclassified into one line item with cash and cash equivalents to conform to presentation as of September 30, 2018. In addition, certain prior period amounts have been reclassified in the condensed consolidated statements of cash flows to conform to the current period presentation. These reclassifications had no material impact on the Company’s consolidated financial position, results of operations, or cash flows as previously reported.

Use of Estimates

The preparation of condensed consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying condensed consolidated financial statements and these notes. Actual results could differ from those estimates and may result in material effects on the Company’s operating results and financial position. Significant estimates made in preparing the accompanying condensed consolidated financial statements include (but are not limited to) those related to revenue recognition, goodwill and long-lived asset impairment assessments, income tax valuations and fair value measurements.

Revenue Recognition

Revenue Recognition Overview



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2018		2017		2018
Volume -related	$	63,123	$	67,827	$	199,987	$	197,805
Station construction sales	12,502		9,359		34,077		20,938
Alternative fuels excise tax credit (“AFTC”)	—		—		—		26,863
Compressor sales	5,919		—		17,640		—
Other	248		134		595		4,584
	$	81,792	$	77,320	$	252,299	$	250,190

Volume -Related

The Company’s volume -related revenue primarily consists of sales of RNG, CNG and LNG fuel, O&M services and RINs and LCFS Credits.

Station Construction Sales

AFTC

Compressor Sales

The Company completed the CEC Combination (as defined in Note 5) during the year ended December 31, 2017 and no longer generates revenue from compressor sales.

Other

Remaining Performance Obligations

Costs to Fulfill a Contract

Contract Balances

As of December 31, 2017 and September 30, 2018, the Company’s contract balances were as follows:



	December 31, 2017		September 30, 2018
Receivables, net	$	63,961	$	69,822

Contract Assets - Current	$	1,603	$	550
Contract Assets - Noncurrent	5,046		3,890
Contract Assets - Total	$	6,649	$	4,440

Contract Liabilities - Current	$	3,432	$	8,830
Contract Liabilities - Noncurrent	13,413		10,682
Contract Liabilities - Total	$	16,845	$	19,512

Receivables, Net

Contract Assets

Contract Liabilities

Recently Adopted Accounting Changes and Recently Issued Accounting Standards

Recently Adopted Accounting Changes



	Balance as of December 31, 2017			Adjustments Due to ASC 606			Balance as of January 1, 2018
Notes receivable and other long-term assets, net	$	21,397		$	(963	)	$	20,434
Deferred revenue	$	3,432		$	330		$	3,762
Accumulated deficit	$	(683,570	)	$	(1,293	)	$	(684,863	)

The ASC 606 adoption adjustments on the accompanying condensed consolidated balance sheet as of September 30, 2018 are as follows:



	September 30, 2018
	Balance before ASC 606 Adoption			Effect of Change			As Reported
Notes receivable and other long-term assets, net	$	16,885		$	(907	)	$	15,978
Deferred revenue	$	7,989		$	841		$	8,830
Accumulated deficit	$	(693,767	)	$	(1,748	)	$	(695,515	)

The impact on the accompanying condensed consolidated statements of operations for the three and nine months ended September 30, 2018 was immaterial.

Recently Issued Accounting Standards

Revenue from Contracts with Customers (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Disaggregation of revenue



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2018		2017		2018
Volume -related	$	63,123	$	67,827	$	199,987	$	197,805
Station construction sales	12,502		9,359		34,077		20,938
Alternative fuels excise tax credit (“AFTC”)	—		—		—		26,863
Compressor sales	5,919		—		17,640		—
Other	248		134		595		4,584
	$	81,792	$	77,320	$	252,299	$	250,190

Summary of contract balances

As of December 31, 2017 and September 30, 2018, the Company’s contract balances were as follows:



	December 31, 2017		September 30, 2018
Receivables, net	$	63,961	$	69,822

Contract Assets - Current	$	1,603	$	550
Contract Assets - Noncurrent	5,046		3,890
Contract Assets - Total	$	6,649	$	4,440

Contract Liabilities - Current	$	3,432	$	8,830
Contract Liabilities - Noncurrent	13,413		10,682
Contract Liabilities - Total	$	16,845	$	19,512

Asset Impairments, Other Charges, and Inventory Valuation Provision (Tables)

9 Months Ended

Sep. 30, 2018

Restructuring and Related Activities [Abstract]

Restructuring and impairment charges

The following table summarizes these charges:



	Three and Nine Months Ended September 30, 2017
Workforce reduction and related charges	$	3,057
CEC asset impairments	32,274
Station closures and related charges	25,335
Total asset impairments and other charges	$	60,666
Inventory valuation provision	13,158
Total charges	$	73,824

Cash Charges



	Charges		Cash Payments Made as of December 31, 2017		Balance as of December 31, 2017		Cash Payments Made as of September 30, 2018			Balance as of September 30, 2018
Employee severance	$	2,757	(2,757	)	$	—	$	—		$	—
Lease termination fees and AROs for station closures	3,861		(70	)	3,791		(1,667		)	2,124
	$	6,618	(2,827	)	$	3,791	(1,667		)	$	2,124

Cash, Cash Equivalents, and Restricted Cash (Tables)

9 Months Ended

Sep. 30, 2018

Cash and Cash Equivalents [Abstract]

Schedule of cash and cash equivalents

Cash, cash equivalents and restricted cash as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Cash and cash equivalents	$	36,081	$	158,143
Restricted cash - standby letters of credit	1,127		1,127
Restricted cash - held in escrow	—		750
Total cash, cash equivalents and restricted cash	$	37,208	$	160,020

Schedule of restricted cash

Cash, cash equivalents and restricted cash as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Cash and cash equivalents	$	36,081	$	158,143
Restricted cash - standby letters of credit	1,127		1,127
Restricted cash - held in escrow	—		750
Total cash, cash equivalents and restricted cash	$	37,208	$	160,020

Short-term Investments (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Summary of short-term investments

Short-term investments as of December 31, 2017 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	21,414	$	(49	)	$	21,365
Zero coupon bonds	54,159		(33		)	54,126
Corporate bonds	55,109		(40		)	55,069
Certificates of deposit	10,902		—			10,902
Total short-term investments	$	141,584	$	(122	)	$	141,462

Short-term investments as of September 30, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	16,351	$	—		$	16,351
Zero coupon bonds	64,871		(2		)	64,869
Corporate bonds	3,721		2			3,723
Certificates of deposit	11,021		—			11,021
Total short-term investments	$	95,964	$	—		$	95,964

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

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

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, 2017 and September 30, 2018, respectively:



Description	Balance at December 31, 2017		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	21,365	$	—	$	21,365	$	—
Zero coupon bonds	54,126		—		54,126		—
Corporate bonds	55,069		—		55,069		—
Certificates of deposit ⁽¹⁾	10,902		—		10,902		—
Liabilities:
Warrants ⁽²⁾	$	536	$	—	$	—	$	536



Description	Balance at September 30, 2018		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	16,351	$	—	$	16,351	$	—
Zero coupon bonds	64,869		—		64,869		—
Corporate bonds	3,723		—		3,723		—
Certificates of deposit ⁽¹⁾	11,021		—		11,021		—
Liabilities:
Warrants ⁽²⁾	$	435	$	—	$	—	$	435

(1) Included in Short-term investments in the accompanying condensed consolidated balance sheets. See Note 7 for more information.

(2) Included in Accrued liabilities and Other long-term liabilities in the accompanying condensed consolidated balance sheets.

Other Receivables (Tables)

9 Months Ended

Sep. 30, 2018

Receivables [Abstract]

Schedule of other receivables

Other receivables as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Loans to customers to finance vehicle purchases	$	4,746	$	5,360
Accrued customer billings	10,072		9,007
Fuel tax credits	177		1,256
Other	4,240		2,267
Total other receivables	$	19,235	$	17,890

Inventory (Tables)

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Schedule of inventories

Inventories as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Raw materials and spare parts	$	35,145	$	37,013
Finished goods	93		90
Total inventories	$	35,238	$	37,103

Land, Property and Equipment (Tables)

9 Months Ended

Sep. 30, 2018

Property, Plant and Equipment [Abstract]

Summary of land, property and equipment

Land, property and equipment as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017			September 30, 2018
Land	$	2,858		$	2,858
LNG liquefaction plants	94,634			94,634
Station equipment	304,090			307,301
Trailers	70,906			71,284
Other equipment	88,313			95,623
Construction in progress	74,905			74,501
	635,706			646,201
Less: accumulated depreciation	(268,401		)	(302,124		)
Total land, property and equipment, net	$	367,305		$	344,077

Accrued Liabilities (Tables)

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Schedule of accrued liabilities

Accrued liabilities as of December 31, 2017 and September 30, 2018 consisted of the following:



	December 31, 2017		September 30, 2018
Accrued alternative fuels incentives ⁽¹⁾	$	2,954	$	5,900
Accrued employee benefits	2,378		3,381
Accrued interest	1,486		4,897
Accrued gas and equipment purchases	8,722		10,560
Accrued property and other taxes	4,582		4,245
Accrued salaries and wages	8,363		6,117
Other ⁽²⁾	13,783		13,222
Total accrued liabilities	$	42,268	$	48,322


(1)	Includes the amount of RINs and LCFS Credits and, as of September 30, 2018, the amount of AFTC payable to third parties. The AFTC expired as of December 31, 2017, but was reinstated in February 2018 for vehicle fuel sales made from January 1, 2017 through December 31, 2017. See Note 19 for more information about AFTC.

(2)

Debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Schedule of debt and capital lease obligations

Debt and capital lease obligations as of December 31, 2017 and September 30, 2018 consisted of the following and are further discussed below:



	December 31, 2017
	Principal Balances			Unamortized Debt Financing Costs			Balance, Net of Financing Costs
7.5% Notes	$	125,000		$	131		$	124,869
5.25% Notes	110,450			454			109,996
NG Advantage debt and capital lease obligations	23,437			259			23,178
Capital lease obligations	802			—			802
Other debt	1,242			—			1,242
Total debt and capital lease obligations	260,931			844			260,087
Less amounts due within one year	(140,223		)	(524		)	(139,699		)
Total long-term debt and capital lease obligations	$	120,708		$	320		$	120,388



	September 30, 2018
	Principal Balances			Unamortized Debt Financing Costs			Balance Net of Financing Costs
7.5% Notes	$	100,000		$	72		$	99,928
5.25% Notes	110,450			2			110,448
NG Advantage debt and capital lease obligations	26,723			292			26,431
Capital lease obligations	809			—			809
Other debt	1,080			—			1,080
Total debt and capital lease obligations	239,062			366			238,696
Less amounts due within one year	(115,951		)	(72		)	(115,879		)
Total long-term debt and capital lease obligations	$	123,111		$	294		$	122,817

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Schedule of information required to compute basic and diluted net loss per share

The information required to compute basic and diluted net loss per share is as follows:



	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2018	2017	2018
Weighted-average common shares outstanding	150,927,825	203,469,222	150,128,204	172,946,896
Dilutive effect of potential common shares from restricted stock units and stock options	—	—	—	—
Weighted-average common shares outstanding -diluted	150,927,825	203,469,222	150,128,204	172,946,896

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



	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2018	2017	2018
Stock Options	9,648,613	9,417,492	9,648,613	9,417,492
Convertible Notes	14,991,521	13,409,242	14,991,521	13,409,242
Restricted Stock Units	2,403,266	2,428,731	2,403,266	2,428,731
Total	27,043,400	25,255,465	27,043,400	25,255,465

Schedule of at-the-market offering program activity

The following table summarizes the activity under the ATM Program for the periods presented:



	Nine Months Ended September 30, 2017
Gross proceeds	$	10,767
Fees and issuance costs	311
Net proceeds	$	10,456
Shares issued	3,802,500

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2018		2017		2018
Stock-based compensation expense, net of $0 tax in 2017 and 2018 ⁽¹⁾	$	2,216	$	1,206	$	6,904	$	4,312

Recently Adopted Accounting Changes and Recently Issued Accounting Standards (Tables)

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Schedule of adoption adjustments



	Balance as of December 31, 2017			Adjustments Due to ASC 606			Balance as of January 1, 2018
Notes receivable and other long-term assets, net	$	21,397		$	(963	)	$	20,434
Deferred revenue	$	3,432		$	330		$	3,762
Accumulated deficit	$	(683,570	)	$	(1,293	)	$	(684,863	)

The ASC 606 adoption adjustments on the accompanying condensed consolidated balance sheet as of September 30, 2018 are as follows:



	September 30, 2018
	Balance before ASC 606 Adoption			Effect of Change			As Reported
Notes receivable and other long-term assets, net	$	16,885		$	(907	)	$	15,978
Deferred revenue	$	7,989		$	841		$	8,830
Accumulated deficit	$	(693,767	)	$	(1,748	)	$	(695,515	)

General (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 160,020	$ 37,208	$ 46,775	$ 43,115
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in restricted cash		1,127
Cash and cash equivalents		$ 1,127

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 77,320	$ 81,792	$ 250,190	$ 252,299
Receivables, net	69,822		69,822			$ 63,961
Contract Assets - Current	550		550			1,603
Contract Assets - Noncurrent	3,890		3,890			5,046
Contract Assets - Total	4,440		4,440			6,649
Contract Liabilities - Current	8,830		8,830		$ 3,762	3,432
Contract Liabilities - Noncurrent	10,682		10,682			13,413
Contract Liabilities - Total	19,512		19,512			$ 16,845
Volume -related
Disaggregation of Revenue [Line Items]
Revenue	67,827	63,123	197,805	199,987
Station construction sales
Disaggregation of Revenue [Line Items]
Revenue	9,359	12,502	20,938	34,077
Alternative fuels excise tax credit (“AFTC”)
Disaggregation of Revenue [Line Items]
Revenue	0	0	26,863	0
Compressor sales
Disaggregation of Revenue [Line Items]
Revenue	0	5,919	0	17,640
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 134	$ 248	$ 4,584	$ 595

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Revenue, remaining performance obligation	$ 11,316	$ 11,316
Capitalized contract cost, gross	7,270	7,270
Capitalized contract cost, accumulated depreciation	4,495	4,495
Capitalized contract cost, amortization	484	1,490
Disaggregation of Revenue [Line Items]
Deferred revenue	8,830	8,830	$ 3,762	$ 3,432
Contract with customer, liability, revenue recognized		1,636
Deferred Revenue
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 3,255	$ 3,255		$ 1,092

Revenue from Contracts with Customers - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01	Sep. 30, 2018
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years

Asset Impairments, Other Charges, and Inventory Valuation Provision - Summary of Charges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Workforce reduction and related charges		$ 3,057		$ 3,057
CEC asset impairments		32,274		32,274
Station closures and related charges		25,335		25,335
Total asset impairments and other charges	$ 0	60,666	$ 0	60,666
Inventory valuation provision	$ 0	13,158	$ 0	13,158
Total charges		$ 73,824		$ 73,824

Asset Impairments, Other Charges, and Inventory Valuation Provision - Cash Related Charges (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Charges		$ 6,618
Cash Payments Made	$ (1,667)	(2,827)
Restructuring Reserve	2,124	3,791
Employee severance
Restructuring Cost and Reserve [Line Items]
Charges		2,757
Cash Payments Made	0	(2,757)
Restructuring Reserve	0	0
Lease termination fees and AROs for station closures
Restructuring Cost and Reserve [Line Items]
Charges		3,861
Cash Payments Made	(1,667)	(70)
Restructuring Reserve	$ 2,124	$ 3,791

Divestitures (Details)				1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	18 Months Ended
Divestitures (Details)	Jun. 22, 2017 USD ($)	Mar. 31, 2017 USD ($)	Feb. 27, 2017 USD ($) facility	Feb. 28, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) shares
Acquisition and Divestitures
Gain from sale of certain assets of subsidiary					$ 0	$ 0	$ 0	$ 69,886,000
Goodwill					$ 64,328,000		$ 64,328,000		$ 64,328,000	$ 64,328,000
BP Products North America, Inc.
Acquisition and Divestitures
Production facilities to be developed \| facility			2
Asset purchase agreement, amount		$ 155,511,000
Extinguishment of debt, amount		8,820,000
Asset purchase agreement, cash paid		30,000,000		$ 871,000						1,007,000
Asset purchase agreement, debt instrument, face amount		123,487,000
Asset purchase agreement, post-closing adjustments, payment	$ 2,010,000
Gain from sale of certain assets of subsidiary									69,886,000	762,000
Asset purchase agreement, contingent consideration (up to)			$ 25,000,000						772,000
Asset purchase agreement, contingent consideration, term			5 years
Asset purchase agreement, payment of transaction costs		$ 3,695,000		$ 65,000						$ 8,605,000
Asset purchase agreement, shares issued (in shares) \| shares				15,877						770,269
Asset purchase agreement, shares issued, value				$ 34,000						$ 1,964,000
Proceeds from sale of other assets										$ 142,190,000
Goodwill									$ 26,576,000

Investments in Other Entities and Noncontrolling Interest in a Subsidiary (Details) - USD ($)			3 Months Ended		9 Months Ended
	Oct. 01, 2018	Jul. 14, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Feb. 28, 2018	Dec. 31, 2017	Dec. 29, 2017	Oct. 14, 2014	Sep. 16, 2014
Acquisition and Divestitures
Gain (loss) from equity method investments			$ (542,000)	$ (30,000)		$ (2,739,000)	$ (100,000)
Post-closing commitments incurred						(1,163,000)	0
Investment balance			27,674,000		$ 27,674,000	27,674,000			$ 30,395,000
Loss from noncontrolling interest			$ 1,300,000	747,000		$ 4,235,000	1,813,000
Common unit purchase agreement \| NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent			53.30%		53.30%	53.30%		53.50%
Common unit purchase agreement \| Subsequent Event \| NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent	61.70%
Mansfield
Acquisition and Divestitures
Ownership interest												50.00%
Gain (loss) from equity method investments			$ 276,000	(30,000)		$ 226,000	(100,000)
Investment balance			1,738,000		$ 1,738,000	1,738,000			1,512,000
SAFE&CEC S.r.l.
Acquisition and Divestitures
Ownership interest										49.00%
Gain (loss) from equity method investments			(817,000)			(2,964,000)
Post-closing commitments incurred					1,163,000
Investment balance			24,936,000		24,936,000	24,936,000			27,883,000
SAFE&CEC S.r.l. \| Landi Renzo S.p.A.
Acquisition and Divestitures
Ownership interest										51.00%
NG Advantage
Acquisition and Divestitures
Loss from noncontrolling interest			1,300,000	$ 747,000		4,235,000	$ 1,813,000
Noncontrolling interest, fair value			$ 18,433,000		$ 18,433,000	$ 18,433,000			$ 22,668,000
NG Advantage \| Common unit purchase agreement
Acquisition and Divestitures
Ownership interest acquired											53.30%
Contingent consideration, liability (up to)								$ 30,000,000
Stock issued during period, acquisitions (in shares)								19,660
NG Advantage \| Common unit purchase agreement \| Subsequent Event
Acquisition and Divestitures
Stock issued during period, acquisitions (in shares)	1,000,001
Payments to acquire additional controlling interest	$ 5,000,000
NG Advantage \| Common unit purchase agreement \| Preferred units
Acquisition and Divestitures
Stock issued during period, value, acquisitions		$ 7,500,000

Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Cash and cash equivalents	$ 158,143,000	$ 36,081,000
Total cash, cash equivalents and restricted cash	160,020,000	37,208,000	$ 46,775,000	$ 43,115,000
Cash in excess of insurance limits	156,795,000	34,709,000
Long-term restricted cash	0	0
Held in Escrow
Line of Credit Facility [Line Items]
Restricted cash	750,000	0
Standby letters of credit
Line of Credit Facility [Line Items]
Restricted cash	$ 1,127,000	$ 1,127,000

Short-term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Short-term investments
Amortized Cost	$ 95,964	$ 141,584
Gross Unrealized Losses	0	(122)
Estimated Fair Value	95,964	141,462
Municipal bonds and notes
Short-term investments
Amortized Cost	16,351	21,414
Gross Unrealized Losses	0	(49)
Estimated Fair Value	16,351	21,365
Zero coupon bonds
Short-term investments
Amortized Cost	64,871	54,159
Gross Unrealized Losses	(2)	(33)
Estimated Fair Value	64,869	54,126
Corporate bonds
Short-term investments
Amortized Cost	3,721	55,109
Gross Unrealized Losses	2	(40)
Estimated Fair Value	3,723	55,069
Certificates of deposit
Short-term investments
Amortized Cost	11,021	10,902
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 11,021	$ 10,902

Fair Value Measurements - Assets and Liabilities (Details) - Fair value measured on recurring basis - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Warrants
Liabilities:
Warrants	$ 435	$ 536
Municipal bonds and notes
Assets:
Available-for-sale debt securities	16,351	21,365
Zero coupon bonds
Assets:
Available-for-sale debt securities	64,869	54,126
Corporate bonds
Assets:
Available-for-sale debt securities	3,723	55,069
Certificates of deposit
Assets:
Available-for-sale debt securities	11,021	10,902
Level 1 \| Warrants
Liabilities:
Warrants	0	0
Level 1 \| Municipal bonds and notes
Assets:
Available-for-sale debt securities	0	0
Level 1 \| Zero coupon bonds
Assets:
Available-for-sale debt securities	0	0
Level 1 \| Corporate bonds
Assets:
Available-for-sale debt securities	0	0
Level 1 \| Certificates of deposit
Assets:
Available-for-sale debt securities	0	0
Level 2 \| Warrants
Liabilities:
Warrants	0	0
Level 2 \| Municipal bonds and notes
Assets:
Available-for-sale debt securities	16,351	21,365
Level 2 \| Zero coupon bonds
Assets:
Available-for-sale debt securities	64,869	54,126
Level 2 \| Corporate bonds
Assets:
Available-for-sale debt securities	3,723	55,069
Level 2 \| Certificates of deposit
Assets:
Available-for-sale debt securities	11,021	10,902
Level 3 \| Warrants
Liabilities:
Warrants	435	536
Level 3 \| Municipal bonds and notes
Assets:
Available-for-sale debt securities	0	0
Level 3 \| Zero coupon bonds
Assets:
Available-for-sale debt securities	0	0
Level 3 \| Corporate bonds
Assets:
Available-for-sale debt securities	0	0
Level 3 \| Certificates of deposit
Assets:
Available-for-sale debt securities	$ 0	$ 0

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Measurements
Impairment of long-lived assets held and used		$ 0	$ 58,119
Fair Value, Measurements, Nonrecurring
Fair Value Measurements
Assets held and used, long lived, at carrying value before write-down	$ 59,367		59,367
Assets held and used, long lived, at fair value after write-down	6,709		6,709
Impairment of long-lived assets held and used	$ 52,658		$ 52,658

Other Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Receivables
Other receivables	$ 17,890	$ 19,235
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	5,360	4,746
Accrued customer billings
Other Receivables
Other receivables	9,007	10,072
Fuel tax credits
Other Receivables
Other receivables	1,256	177
Other
Other Receivables
Other receivables	$ 2,267	$ 4,240

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials and spare parts	$ 37,013	$ 35,145
Finished goods	90	93
Total inventories	$ 37,103	$ 35,238

Land, Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Land, Property and Equipment
Land, property and equipment, gross	$ 646,201		$ 646,201		$ 635,706
Less: accumulated depreciation	(302,124)		(302,124)		(268,401)
Total land, property and equipment, net	344,077		344,077		367,305
Capitalized software costs	28,910		28,910		26,003
Accumulated amortization on the capitalized software costs	21,424		21,424		18,737
Amortization expense related to the capitalized software costs	1,026	$ 1,140	2,699	$ 3,134
Property and equipment purchases included in accounts payable and accrued liabilities	1,660		1,660		2,007
Land
Land, Property and Equipment
Land, property and equipment, gross	2,858		2,858		2,858
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,634		94,634		94,634
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	307,301		307,301		304,090
Trailers
Land, Property and Equipment
Land, property and equipment, gross	71,284		71,284		70,906
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	95,623		95,623		88,313
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 74,501		$ 74,501		$ 74,905

Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 5,900	$ 2,954
Accrued employee benefits	3,381	2,378
Accrued interest	4,897	1,486
Accrued gas and equipment purchases	10,560	8,722
Accrued property and other taxes	4,245	4,582
Accrued salaries and wages	6,117	8,363
Other	13,222	13,783
Total accrued liabilities	$ 48,322	$ 42,268

Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2013	Jul. 11, 2011
Long-term debt
Principal Balances	$ 239,062	$ 260,931
Unamortized Debt Financing Costs	366	844
Balance, Net of Financing Costs	238,696	260,087
Principal Balances, amounts due within one year	(115,951)	(140,223)
Unamortized Debt Financing Costs, amounts due within one year	(72)	(524)
Balance, Net of Financing Costs, amounts due within one year	(115,879)	(139,699)
Principal Balances, long-term	123,111	120,708
Unamortized Debt Financing Costs, long-term	294	320
Balance, Net of Financing Costs, long-term	122,817	120,388
7.5% Notes
Long-term debt
Principal Balances	100,000	125,000
Unamortized Debt Financing Costs	72	131
Balance, Net of Financing Costs	$ 99,928	124,869
Interest rate	7.50%			7.50%
5.25% Notes
Long-term debt
Principal Balances	$ 110,450	110,450
Unamortized Debt Financing Costs	2	454
Balance, Net of Financing Costs	$ 110,448	109,996
Interest rate	5.25%		5.25%
NG Advantage debt and capital lease obligations
Long-term debt
Principal Balances	$ 26,723	23,437
Unamortized Debt Financing Costs	292	259
Balance, Net of Financing Costs	26,431	23,178
Capital lease obligations
Long-term debt
Principal Balances	809	802
Unamortized Debt Financing Costs	0	0
Balance, Net of Financing Costs	809	802
Other debt
Long-term debt
Principal Balances	1,080	1,242
Unamortized Debt Financing Costs	0	0
Balance, Net of Financing Costs	$ 1,080	$ 1,242

Debt - 7.5% Notes (Details) - 7.5% Notes					9 Months Ended
Debt - 7.5% Notes (Details) - 7.5% Notes	Jun. 29, 2018 USD ($)	Feb. 09, 2017 USD ($)	Jun. 14, 2013 USD ($) day $ / shares shares	Jul. 11, 2011 USD ($) note	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Nov. 17, 2017 USD ($)	Feb. 21, 2017 USD ($)	Aug. 27, 2013 USD ($)
Long-term debt
Interest rate				7.50%		7.50%
Financing commitment received (up to)				$ 150,000,000
Number of debt instruments \| note				3
Financing commitment, issuance period				3 years
Principal amount of each debt instrument to be issued				$ 50,000,000
Buyers
Long-term debt
Additional amount of advances under the obligation assumed			$ 50,000,000
Amount of advance funded			$ 50,000,000
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 (at least) \| day			20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion \| day			30
Period during which the debt instrument principal balance is required to be paid following its issuance			7 years
Repayment in shares at maturity covenant, maximum number of shares (in shares) \| shares			13,993,630
Green Energy Investment Holdings, LLC
Long-term debt
Principal amount transferred								$ 11,800,000	$ 5,000,000
Debt instrument, repurchase amount during period	$ 25,000,000
Payment of accrued and unpaid interest	$ 505,000
Aggregate principal amount						$ 56,435,000
Green Energy Investment Holdings, LLC \| Boone Pickens
Long-term debt
Principal amount transferred							$ 40,000,000
Debt instrument, repurchase amount during period		$ 25,000,000
Payments for repurchase and retirement of debt instrument		$ 21,750,000
Gain on repurchase of debt instrument					$ 3,191,000
Other Third Parties
Long-term debt
Aggregate principal amount									$ 43,565,000

Debt - 5.25% Notes (Details) - 5.25% Notes - USD ($)		1 Months Ended	61 Months Ended
Debt - 5.25% Notes (Details) - 5.25% Notes - USD ($)	Oct. 01, 2018	Sep. 30, 2013	Sep. 29, 2018	Sep. 30, 2018
Long-term debt
Interest rate		5.25%		5.25%
Debt issuance amount		$ 250,000,000
Payment of certain debt issuance costs		7,805,000
Amount of advance funded		$ 242,195,000
Payments for repurchase and retirement of debt instrument			$ 84,344,000
Debt instrument, repurchase amount during period			$ 114,550,000
Stock issued during period (in shares)			6,265,829
Common stock exchange, face amount exchanged during period			$ 25,000,000
Subsequent Event
Long-term debt
Debt instrument, repurchase amount during period	$ 110,450,000
Payment of accrued and unpaid interest	$ 2,899,000
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 (at least)		25.00%

Debt - Plains Credit Facility (Details) - Plains Credit Facility - USD ($)	Feb. 29, 2016	Dec. 22, 2016
Long-term debt
Line of credit limit	$ 50,000,000
Line of credit		$ 23,500,000
Interest rate	2.70%
LIBOR
Long-term debt
Percentage of margin added to reference rate to determine interest rate on debt	2.30%

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Debt - Other Debt (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Mar. 19, 2014
Trailer and Equipment Debt
Long-term debt
Weighted average interest rate	5.89%	4.98%
Trailer and Equipment Debt \| Maximum
Long-term debt
Interest rate	8.76%
Other Debt
Long-term debt
Weighted average interest rate	4.79%	4.79%
Other Debt \| Maximum
Long-term debt
Interest rate	5.02%
Canton Renewables \| Canton Bonds
Long-term debt
Debt issuance amount			$ 12,400,000

Net Loss Per Share (Details) - USD ($)	3 Months Ended		9 Months Ended
Net Loss Per Share (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 21, 2016
Earnings Per Share [Abstract]
Weighted-average common shares outstanding (in shares)	203,469,222	150,927,825	172,946,896	150,128,204
Dilutive effect of potential common shares from restricted stock units and stock options (in shares)	0	0	0	0
Weighted-average common shares outstanding - diluted (in shares)	203,469,222	150,927,825	172,946,896	150,128,204
Citigroup Global Markets Inc. \| Equity Distribution Agreement
Securities Financing Transaction [Line Items]
Equity financing agreement, amount authorized (up to)					$ 200,000,000
Gross proceeds				$ 10,767,000
Fees and issuance costs				311,000
Net proceeds				$ 10,456,000
Shares issued (in shares)				3,802,500

Net Loss Per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Loss Per Share
Anti-dilutive securities (in shares)	25,255,465	27,043,400	25,255,465	27,043,400
Stock Options
Net Loss Per Share
Anti-dilutive securities (in shares)	9,417,492	9,648,613	9,417,492	9,648,613
Convertible Notes
Net Loss Per Share
Anti-dilutive securities (in shares)	13,409,242	14,991,521	13,409,242	14,991,521
Restricted Stock Units
Net Loss Per Share
Anti-dilutive securities (in shares)	2,428,731	2,403,266	2,428,731	2,403,266

Stock-Based Compensation (Details) - USD ($)	3 Months Ended		9 Months Ended
Stock-Based Compensation (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense, net of $0 tax in 2017 and 2018	$ 1,206,000	$ 2,216,000	$ 4,312,000	$ 6,904,000
Stock-based compensation expense, tax	0	0	0	0
Unrecognized compensation cost	$ 5,242,000		$ 5,242,000
Unrecognized compensation cost, weighted-average period			1 year 10 months 2 days
Restructuring Costs and Asset Impairment Charges
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense, net of $0 tax in 2017 and 2018		$ 300,000		$ 300,000

Stockholders’ Equity (Details) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Jun. 13, 2018	May 09, 2018	Sep. 30, 2017
Equity Distribution Agreement \| Citigroup Global Markets Inc.
Subsidiary, Sale of Stock [Line Items]
Fees and issuance costs			$ 311
Shares issued (in shares)			3,802,500
Gross proceeds from shares sold			$ 10,767
Purchase Agreement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)		50,856,296
Price per share (in dollars per share)		$ 1.64
Percentage of ownership after transaction	25.00%
Consideration received on transaction	$ 83,404
Fees and issuance costs	$ 2,694
Purchase Agreement \| Purchase Percentage Covenant, Threshold
Subsidiary, Sale of Stock [Line Items]
Percentage of ownership after transaction		5.00%
Purchase Agreement \| Purchase Percentage Covenant, Maximum
Subsidiary, Sale of Stock [Line Items]
Percentage of ownership after transaction		30.00%

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax benefit (expense)	$ (89)	$ 44	$ (266)	$ 2,183
Decrease in deferred tax liability, reduction in goodwill					$ 2,493
Decrease in deferred tax assets, operating loss carryforwards					29,768
Decrease in deferred tax asset valuation allowance					$ 29,768
Unrecognized tax benefits, increase from portion of AFTC revenue offset by the fuel tax			$ 2,178

Alternative Fuels Excise Tax Credit (Details) $ in Thousands	8 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 $ / gallon	Dec. 31, 2016 $ / gallon	Dec. 31, 2015 $ / gallon
Alternative Fuels Excise Tax Credit
Federal alternative fuels tax credit - CNG (in dollars per gasoline gallon equivalent)					0.50
Federal alternative fuels tax credit - LNG (in dollars per liquid gallon)			0.50	0.50	0.50
Federal alternative fuels tax credit - credits recognized as revenue \| $	$ 25,481	$ 1,382

Recently Adopted Accounting Changes and Recently Issued Accounting Standards (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Notes receivable and other long-term assets, net		$ 15,978	$ 20,434	$ 21,397
Deferred revenue		8,830	3,762	3,432
Accumulated deficit		(695,515)	(684,863)	(683,570)
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Notes receivable and other long-term assets, net		16,885		21,397
Deferred revenue		7,989		3,432
Accumulated deficit		(693,767)		$ (683,570)
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in net cash flows	$ 5,533
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Notes receivable and other long-term assets, net		(907)	(963)
Deferred revenue		841	330
Accumulated deficit		$ (1,748)	$ (1,293)

Subsequent Events (Details) - Designated as Hedging Instrument - Commodity Contract - Subsequent Event	1 Months Ended
	Oct. 31, 2018 contract gal
Subsequent Event [Line Items]
Number of contracts held \| contract	2
Notional amount, volume \| gal	5,000,000