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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	May 02, 2019
Document and Entity Information
Entity Registrant Name	Clean Energy Fuels Corp.
Entity Central Index Key	0001368265
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
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)		204,654,228
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash, cash equivalents and current portion of restricted cash	$ 28,763	$ 30,624
Short-term investments	66,164	65,646
Accounts receivable, net of allowance for doubtful accounts of $1,919 and $1,984 as of December 31, 2018 and March 31, 2019, respectively	70,341	68,865
Other receivables	9,198	15,544
Derivative assets, related party	728	1,508
Inventory	32,653	34,975
Prepaid expenses and other current assets	8,769	8,444
Total current assets	216,616	225,606
Operating lease right-of-use assets	23,801
Land, property and equipment, net	338,192	350,568
Long-term portion of restricted cash	4,848	4,000
Notes receivable and other long-term assets, net	16,948	17,470
Long-term portion of derivative assets, related party	4,634	8,824
Investments in other entities	25,842	26,079
Goodwill	64,328	64,328
Intangible assets, net	1,951	2,207
Total assets	697,160	699,082
Current liabilities:
Current portion of debt	5,344	4,712
Current portion of finance lease obligations		693
Current portion of finance lease obligations	695
Current portion of operating lease obligations	3,545
Accounts payable	15,413	19,024
Accrued liabilities	36,754	48,469
Deferred revenue	6,858	7,361
Total current liabilities	68,609	80,259
Long-term portion of debt	76,501	75,003
Long-term portion of finance lease obligations		3,776
Long-term portion of finance lease obligations	3,718
Long-term portion of operating lease obligations	21,621
Other long-term liabilities	12,732	15,035
Total liabilities	183,181	174,073
Commitments and contingencies (Note 17)
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 304,000,000 shares as of December 31, 2018 and March 31, 2019, respectively; issued and outstanding 203,599,892 shares and 204,651,932 shares as of December 31, 2018 and March 31, 2019, respectively	20	20
Additional paid-in capital	1,200,418	1,198,769
Accumulated deficit	(699,599)	(688,653)
Accumulated other comprehensive loss	(1,764)	(2,138)
Total Clean Energy Fuels Corp. stockholders’ equity	499,075	507,998
Noncontrolling interest in subsidiary	14,904	17,011
Total stockholders’ equity	513,979	525,009
Total liabilities and stockholders’ equity	$ 697,160	$ 699,082

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,984	$ 1,919
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	304,000,000
Common stock, issued (in shares)	204,651,932	203,599,892
Common stock, outstanding (in shares)	204,651,932	203,599,892

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue:
Total revenue	$ 77,698	$ 102,403
Cost of sales (exclusive of depreciation and amortization shown separately below):
Change in fair value of derivative warrants	1,614	(21)
Selling, general and administrative	18,434	18,858
Depreciation and amortization	12,479	12,801
Total operating expenses	91,355	86,434
Operating income (loss)	(13,657)	15,969
Interest expense	(1,891)	(4,503)
Interest income	580	575
Other income (expense), net	2,670	(12)
Loss from equity method investments	(467)	(1,468)
Income (loss) before income taxes	(12,765)	10,561
Income tax expense	(60)	(88)
Net income (loss)	(12,825)	10,473
Loss attributable to noncontrolling interest	1,879	1,749
Net income (loss) attributable to Clean Energy Fuels Corp.	$ (10,946)	$ 12,222
Income (loss) per share:
Basic (in dollars per share)	$ (0.05)	$ 0.08
Diluted (in dollars per share)	$ (0.05)	$ 0.08
Weighted-average common shares outstanding:
Basic (in shares)	204,196,669	152,194,695
Diluted (in shares)	204,196,669	156,643,092
Product revenue
Revenue:
Total revenue	$ 68,448	$ 92,251
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	54,430	50,199
Service revenue
Revenue:
Total revenue	9,250	10,152
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	$ 4,398	$ 4,597

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net income (loss)	$ (12,825)	$ 10,473
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2018 and 2019	308	(78)
Unrealized gains on available-for-sale securities, net of $0 tax in 2018 and 2019	66	53
Total other comprehensive income (loss)	374	(25)
Comprehensive income (loss)	(12,451)	10,448
Clean Energy Fuels Corp.
Net income (loss)	(10,946)	12,222
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2018 and 2019	308	(78)
Unrealized gains on available-for-sale securities, net of $0 tax in 2018 and 2019	66	53
Total other comprehensive income (loss)	374	(25)
Comprehensive income (loss)	(10,572)	12,197
Noncontrolling Interest
Net income (loss)	(1,879)	(1,749)
Other comprehensive income, net of tax:
Comprehensive income (loss)	$ (1,879)	$ (1,749)

- 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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+ Details

Condensed Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, tax	$ 0	$ 0
Unrealized (losses) gains on available-for-sale securities, tax	$ 0	$ 0

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiary
Beginning balance (in shares) at Dec. 31, 2017		151,650,969
Beginning balance at Dec. 31, 2017	$ 449,658	$ 15	$ 1,111,432	$ (683,570)	$ (887)	$ 22,668
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		863,581
Issuance of common stock, net of offering costs	110		110
Stock-based compensation	1,898		1,898
Net income (loss)	10,473			12,222		(1,749)
Other comprehensive income (loss)	(25)				(25)
Ending balance (in shares) at Mar. 31, 2018		152,514,550
Ending balance at Mar. 31, 2018	$ 460,821	$ 15	1,113,440	(672,641)	(912)	20,919
Beginning balance (in shares) at Dec. 31, 2018	203,599,892	203,599,892
Beginning balance at Dec. 31, 2018	$ 525,009	$ 20	1,198,769	(688,653)	(2,138)	17,011
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		1,052,040
Issuance of common stock, net of offering costs	175		175
Stock-based compensation	1,246		1,246
Net income (loss)	(12,825)			(10,946)		(1,879)
Other comprehensive income (loss)	$ 374				374
Increase in ownership in subsidiary			228			(228)
Ending balance (in shares) at Mar. 31, 2019	204,651,932	204,651,932
Ending balance at Mar. 31, 2019	$ 513,979	$ 20	$ 1,200,418	$ (699,599)	$ (1,764)	$ 14,904

- Definition

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

+ References

+ Details

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ (12,825)	$ 10,473
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	12,479	12,801
Provision for doubtful accounts, notes and inventory	300	227
Stock-based compensation expense	1,246	1,898
Change in fair value of derivative instruments	6,584	(21)
Amortization of discount and debt issuance cost	(150)	198
Loss (gain) on disposal of property and equipment	(2,680)	866
Loss from equity method investments	467	1,468
Changes in operating assets and liabilities:
Accounts and other receivables	(5)	(36,796)
Inventory	2,023	(2,704)
Prepaid expenses and other assets	558	(1,525)
Accounts payable	(1,208)	3,970
Deferred revenue	(3,485)	3,914
Accrued expenses and other	(11,533)	2,882
Net cash used in operating activities	(8,229)	(2,349)
Cash flows from investing activities:
Purchases of short-term investments	(26,659)	(41,723)
Maturities and sales of short-term investments	26,396	55,181
Purchases of and deposits on property and equipment	(4,316)	(7,131)
Payments on and proceeds from sales of loans receivable	141	84
Cash received from sale of certain assets of subsidiary, net	5,114	871
Proceeds from disposal of property and equipment	4,388	0
Net cash provided by investing activities	5,064	7,282
Cash flows from financing activities:
Issuances of common stock	175	0
Fees paid for issuances of common stock and debt issuance costs	(15)	0
Proceeds from debt instruments	3,394	6,261
Repayment of finance lease obligations and debt instruments	(1,475)	(1,234)
Net cash provided by financing activities	2,079	5,027
Effect of exchange rates on cash, cash equivalents and restricted cash	73	(72)
Net increase (decrease) in cash, cash equivalents and restricted cash	(1,013)	9,888
Cash, cash equivalents and restricted cash, beginning of period	34,624	37,208
Cash, cash equivalents and restricted cash, end of period	33,611	47,096
Supplemental disclosure of cash flow information:
Income taxes paid	0	24
Interest paid, net of approximately $33 and $80 capitalized, respectively	$ 1,756	$ 2,856

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Cash Flows [Abstract]
Interest paid, capitalized	$ 80	$ 33

General	3 Months Ended
General	Mar. 31, 2019
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. 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 March 31, 2019, and results of operations, comprehensive income (loss) and cash flows for the three months ended March 31, 2018 and 2019. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three month periods ended March 31, 2018 and 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 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, 2018 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 12, 2019. Reclassifications Certain prior period amounts have been reclassified in the condensed consolidated balance sheets and condensed consolidated statements of operations and 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, fair value measurements, goodwill and long-lived asset valuations and impairment assessments, income tax valuations and stock-based compensation expense.

Revenue from Contracts with Customers

3 Months Ended

Mar. 31, 2019

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. 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 revenue disaggregated by revenue source. The Company is generally the principal in its customer contracts because 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 March 31,
	2018		2019
Volume -related ⁽¹⁾	$	67,219	$	74,528
Station construction sales	5,798		3,170
Alternative fuels excise tax credit (“AFTC”)	25,481		—
Other	3,905		—
Total revenue	$	102,403	$	77,698

⁽¹⁾ Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. The amounts are classified as revenue because the Company’s commodity swap contracts are used to economically offset the risk associated with the diesel -to -natural gas price spread resulting from anticipated customer fueling contracts under the Company’s Zero Now truck financing program. See Note 6 for more information about these derivative instruments. For the three months ended March 31, 2018 and 2019, changes in the fair value of commodity swaps amounted to a loss of $0 and $4,970, respectively.

Remaining Performance Obligations

Remaining performance obligations represent the transaction price of customer orders for which the work has not been performed. As of March 31, 2019, the aggregate amount of the transaction price allocated to remaining performance obligations was $10,494, 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.

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 three months ended March 31, 2019, were not materially impacted by any factors outside the normal course of business.

As of December 31, 2018 and March 31, 2019, the Company’s contract balances were as follows:



	December 31, 2018		March 31, 2019
Receivables, net	$	68,865	$	70,341

Contract Assets - Current	$	656	$	843
Contract Assets - Noncurrent	3,825		3,740
Contract Assets - Total	$	4,481	$	4,583

Contract Liabilities - Current	$	5,513	$	5,015
Contract Liabilities - Noncurrent	9,844		6,861
Contract Liabilities - Total	$	15,357	$	11,876

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 payments received primarily from a customer of NG Advantage, LLC (“NG Advantage”) in advance of the performance obligations. Deferred revenue is classified as current or noncurrent based on when the revenue is expected to be recognized. The current portion and noncurrent portion of deferred revenue are included in “Deferred revenue” and “Other long -term liabilities,” respectively, in the accompanying condensed consolidated balance sheets.

Revenue recognized during the three months ended March 31, 2018 related to the Company’s contract liability balances as of December 31, 2017 was $1,842. The decrease in the contract liabilities balance for the three months ended March 31, 2019 is primarily driven by billings in excess of revenue recognized, offset by $3,317 of revenue recognized related to the Company’s contract liability balances as of December 31, 2018.

Investments in Other Entities and Noncontrolling Interest in a Subsidiary	3 Months Ended
	Mar. 31, 2019
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 IMW Industries Ltd. (formerly known as Clean Energy Compression Corp.) (“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 $1,441 and $440 for the three months ended March 31, 2018 and 2019, respectively. The Company has an investment balance in SAFE&CEC S.r.l. of $23,372 and $23,161 as of December 31, 2018 and March 31, 2019, 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. NG Advantage has entered into an arrangement with BP Products North America (“BP”) for the supply, sale and reservation of a specified volume of CNG transportation capacity until March 2022. On February 28, 2018, the Company entered into a guaranty agreement with NG Advantage and BP pursuant to which the Company guarantees NG Advantage’s payment obligations to BP in the event of default by NG Advantage under the supply arrangement, in an amount up to an aggregate of $30,000 plus related fees. This guaranty is in effect until thirty days following the Company’s notice to BP of its termination. As initial 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%. In each month from November 2018 through February 2019, the Company was issued 100,000 additional common units of NG Advantage, for a total of 400,000 common units, pursuant to the guaranty agreement entered in February 2018. The issuance of 400,000 additional common units increased the Company’s controlling interest in NG Advantage to 64.6% as of March 31, 2019. On February 15, 2019, NG Advantage and the Company entered into a transaction pursuant to which the Company agreed to lend to NG Advantage up to $5,000 in accordance with the terms of a delayed draw convertible promissory note (the “2019 Note”). NG Advantage simultaneously drew $2,500 under the 2019 Note, and on April 15, 2019, NG Advantage drew the remaining $2,500 under the 2019 Note. All unpaid principal and accrued interest under the 2019 Note is due and payable on the earlier of February 15, 2023 or in the event of default. The Company may convert the outstanding principal and accrued interest under the 2019 Note at any time prior to payment in full into common units of NG Advantage. The Company recorded a loss attributable to the noncontrolling interest in NG Advantage of $1,749 and $1,879 for the three months ended March 31, 2018 and 2019, respectively. The value of the noncontrolling interest was $17,011 and $14,904 as of December 31, 2018 and March 31, 2019, respectively.

Cash, Cash Equivalents, and Restricted Cash

3 Months Ended

Mar. 31, 2019

Cash and Cash Equivalents [Abstract]

Cash, Cash Equivalents, and Restricted Cash

Cash, cash equivalents and restricted cash as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Current assets:
Cash and cash equivalents	$	29,844	$	27,983
Restricted cash - standby letter of credit	30		30
Restricted cash - held in escrow	750		750
Total cash, cash equivalents and current portion of restricted cash	$	30,624	$	28,763

Long-term assets:
Restricted cash - standby letter of credit	$	4,000	$	4,000
Restricted cash - held in escrow	—		848
Total long-term portion of restricted cash	$	4,000	$	4,848

Total cash, cash equivalents and restricted cash	$	34,624	$	33,611

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 $28,524 and $26,658 as of December 31, 2018 and March 31, 2019, 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 Investments

3 Months Ended

Mar. 31, 2019

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 March 31, 2019, the Company believes its carrying values for its available-for-sale debt securities are properly recorded.

Short-term investments as of December 31, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	9,210	$	(19	)	$	9,191
Zero coupon bonds	29,823		(28		)	29,795
Corporate bonds	26,175		(22		)	26,153
Certificates of deposit	507		—			507
Total short-term investments	$	65,715	$	(69	)	$	65,646

Short-term investments as of March 31, 2019 consisted of the following:



	Amortized Cost		Gross Unrealized Gains (Losses)			Estimated Fair Value
Municipal bonds and notes	$	20,458	$	2		$	20,460
Zero coupon bonds	23,466		(3		)	23,463
Corporate bonds	21,736		(2		)	21,734
Certificates of deposit	507		—			507
Total short-term investments	$	66,167	$	(3	)	$	66,164

Derivative Instruments and Hedging Activities

3 Months Ended

Mar. 31, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments and Hedging Activities

In October 2018, the Company executed two commodity swap contracts with Total Gas & Power North America, an affiliate of TOTAL and THUSA (as defined in Notes 15 and 12, respectively), 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 diesel price fluctuation risks related to the natural gas fuel supply commitments the Company makes in its fueling agreements with fleet operators that participate in the Zero Now truck financing program. These contracts are not designated as accounting hedges and as a result, changes in the fair value of derivative instruments are recognized as earnings in “Product revenue” in the accompanying condensed consolidated statements of operations.

Commodity derivatives as of December 31, 2018 consisted of the following:



	Gross Amounts Recognized		Gross Amounts Offset		Net Amount Presented
Assets:
Current portion of derivative assets, related party	$	1,508	$	—	$	1,508
Long-term portion of derivative assets, related party	8,824		—		8,824
Total derivative assets	$	10,332	$	—	$	10,332

Commodity derivatives as of March 31, 2019 consisted of the following:



	Gross Amounts Recognized		Gross Amounts Offset		Net Amount Presented
Assets:
Current portion of derivative assets, related party	$	728	$	—	$	728
Long-term portion of derivative assets, related party	4,634		—		4,634
Total derivative assets	$	5,362	$	—	$	5,362

As of December 31, 2018 and March 31, 2019, the Company had a total volume on open commodity swap contracts of 25 million diesel gallons at a weighted -average price of approximately $3.18 per gallon, respectively.

The following table reflects the weighted -average price of open commodity swap contracts as of December 31, 2018 and March 31, 2019, by year with associated volumes, respectively:



	December 31, 2018			March 31, 2019
Year	Volumes (Diesel Gallons)	Weighted -Average Price per Diesel Gallon		Volumes (Diesel Gallons)	Weighted -Average Price per Diesel Gallon
2019	3,125,000	$	3.18	3,125,000	$	3.18
2020	5,000,000	$	3.18	5,000,000	$	3.18
2021	5,000,000	$	3.18	5,000,000	$	3.18
2022	5,000,000	$	3.18	5,000,000	$	3.18
2023	5,000,000	$	3.18	5,000,000	$	3.18
2024	1,875,000	$	3.18	1,875,000	$	3.18

Fair Value Measurements

3 Months Ended

Mar. 31, 2019

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 used the income approach to value its outstanding commodity swap contracts (see Note 6). Under the income approach, the Company used a discounted cash flow (“DCF”) model in which cash flows anticipated over the term of the contracts are discounted to their present value using an expected discount rate. The discount rate used for cash flows reflects the specific risks in spot and forward rates and credit valuation adjustments. This valuation approach is considered a Level 3 fair value measurement. The significant unobservable inputs used in the fair value measurement of the Company’s derivative instruments are Ultra-Low Sulfur Diesel (“ULSD”) forward prices and differentials from ULSD to Petroleum Administration for Defense District (“PADD”) regions. Significant increases (decreases) in any of those inputs in isolation would result in a significantly lower (higher) fair value measurement. Generally, a change in the ULSD forward prices is accompanied by a directionally opposite but less extreme change in the ULSD-PADD differential.

The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2018 and March 31, 2019, respectively:



	December 31, 2018			March 31, 2019
Significant Unobservable Inputs	Input Range	Weighted Average		Input Range	Weighted Average
ULSD Gulf Coast Forward Curve	$1.71 - $1.79	$	1.75	$1.90 - $1.96	$	1.93
Historical Differential to PADD 3 Diesel	$0.76 - $1.16	$	0.89	$0.76 - $1.16	$	0.89
Historical Differential to PADD 5 Diesel	$1.22 - $2.12	$	1.55	$1.25 - $2.14	$	1.59

The Company’s liability-classified warrants (which were all issued by NG Advantage) 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 or liabilities between Level 1, Level 2, or Level 3 of the fair value hierarchy as of December 31, 2018 or March 31, 2019.

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, 2018 and March 31, 2019, respectively:



	December 31, 2018		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities ⁽¹⁾:
Municipal bonds and notes	$	9,191	$	—	$	9,191	$	—
Zero coupon bonds	29,795		—		29,795		—
Corporate bonds	26,153		—		26,153		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	10,332		—		—		10,332
Liabilities:
Warrants ⁽³⁾	$	1,079	$	—	$	—	$	1,079



	March 31, 2019		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	20,460	$	—	$	20,460	$	—
Zero coupon bonds	23,463		—		23,463		—
Corporate bonds	21,734		—		21,734		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	5,362		—		—		5,362
Liabilities:
Warrants ⁽³⁾	$	2,693	$	—	$	—	$	2,693

(1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information.

(2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” in the accompanying condensed consolidated balance sheets. See Note 6 for more information.

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

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



	Assets: Commodity Swap Contracts			Liabilities: Warrants
Balance as of December 31, 2017	$	—		$	(536	)
Gain (loss) included in earnings	—			21
Balance as of March 31, 2018	$	—		$	(515	)

Balance as of December 31, 2018	$	10,332		$	(1,079	)
Gain (loss) included in earnings	(4,970		)	(1,614		)
Balance as of March 31, 2019	$	5,362		$	(2,693	)

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, 2018 and March 31, 2019. 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 12 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

3 Months Ended

Mar. 31, 2019

Receivables [Abstract]

Other Receivables

Other receivables as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Loans to customers to finance vehicle purchases	$	276	$	1,887
Accrued customer billings	6,261		5,382
Fuel tax credits	434		434
Other	8,573		1,495
Total other receivables	$	15,544	$	9,198

- 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

3 Months Ended

Mar. 31, 2019

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.

Inventory as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Raw materials and spare parts	$	34,890	$	32,565
Finished goods	85		88
Total inventory	$	34,975	$	32,653

Land, Property and Equipment

3 Months Ended

Mar. 31, 2019

Property, Plant and Equipment [Abstract]

Land, Property and Equipment

Land, property and equipment as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018			March 31, 2019
Land	$	3,681		$	3,681
LNG liquefaction plants	94,633			94,633
Station equipment	319,119			315,694
Trailers	75,901			75,221
Other equipment	97,268			97,793
Construction in progress	73,485			74,346
	664,087			661,368
Less: accumulated depreciation	(313,519		)	(323,176		)
Total land, property and equipment, net	$	350,568		$	338,192

Included in “Land, property and equipment, net” are capitalized software costs of $29,344 and $29,573 as of December 31, 2018 and March 31, 2019, respectively. Accumulated amortization of the capitalized software costs is $22,472 and $23,504 as of December 31, 2018 and March 31, 2019, respectively.

The Company recorded amortization expense related to the capitalized software costs of $718 and $1,035 for the three months ended March 31, 2018 and 2019, respectively.

As of March 31, 2018 and 2019, $939 and $2,163, respectively, are included in “Accounts payable” and “Accrued liabilities,” 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

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Accrued Liabilities

Accrued liabilities as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Accrued alternative fuels incentives	$	6,923	$	5,969
Accrued employee benefits	2,248		2,673
Accrued interest	78		1,135
Accrued gas and equipment purchases	12,833		8,577
Accrued property and other taxes	3,397		3,001
Accrued salaries and wages	8,609		4,159
Other	14,381		11,240
Total accrued liabilities	$	48,469	$	36,754

Debt

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Debt

Debt obligations as of December 31, 2018 and March 31, 2019 consisted of the following and are further discussed below:



	December 31, 2018
	Principal Balances			Unamortized Debt Financing Costs			Balance, Net of Financing Costs
7.5% Notes	$	50,000		$	58		$	49,942
NG Advantage debt	28,904			155			28,749
Other debt	1,024			—			1,024
Total debt	79,928			213			79,715
Less amounts due within one year	(4,811		)	(99		)	(4,712		)
Total long-term debt	$	75,117		$	114		$	75,003



	March 31, 2019
	Principal Balances			Unamortized Debt Financing Costs			Balance Net of Financing Costs
7.5% Notes	$	50,000		$	48		$	49,952
NG Advantage debt	31,065			141			30,924
Other debt	969			—			969
Total debt	82,034			189			81,845
Less amounts due within one year	(5,402		)	(58		)	(5,344		)
Total long-term debt	$	76,632		$	131		$	76,501

7.5% Notes

In June 2013, the Company issued notes (the “7.5% Notes”) to T. Boone Pickens and Green Energy Investment Holdings, LLC (“GEIH”) in the amount of $150,000. The 7.5% Notes 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 7.5% Notes include 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 March 31, 2019.

Prior to January 1, 2018, (i) the Company purchased $25,000 of the 7.5% Notes from Mr. Pickens, (ii) Mr. Pickens transferred all remaining balance of his 7.5% Notes to third parties, and (iii) GEIH transferred $16,800 in principal amount of its 7.5% Notes to third parties.

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 purchased 7.5% Notes were canceled in full.

On December 4, 2018, the Company purchased from the holders thereof all outstanding 7.5% Notes due July 2019, having an aggregate outstanding principal amount of $50,000, for a cash purchase price of $50,500. Upon such purchase, the purchased 7.5% Notes were canceled in full.

As a result of the foregoing transactions, as of March 31, 2019, (i) GEIH held 7.5% Notes in an aggregate principal amount of $32,906, and (ii) other third parties held 7.5% Notes in an aggregate principal amount of $17,094, all of which are due June 2020.

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”). The Company had no amounts outstanding under the Credit Facility as of March 31, 2019.

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 that the Company holds in an account at Plains. There are certain covenants and events of default associated with the Plains LSA. No events of default under the Plains LSA had occurred as of March 31, 2019.

Société Générale Term Loan Facility

On January 2, 2019, the Company entered into a term credit agreement (the “Credit Agreement”) with Société Générale, a company incorporated as a société anonyme under the laws of France (“SG”). The Credit Agreement provides for a term loan facility (the “SG Facility”) pursuant to which the Company may obtain, subject to certain conditions, up to $100,000 of loans (“Loans”) in support of its Zero Now truck financing program. Under the Credit Agreement, the Company is permitted to use the proceeds from the Loans solely to fund the incremental cost of trucks purchased or financed under the Zero Now truck financing program and related fees and expenses incurred by the Company in connection therewith. Interest on outstanding Loans accrues at a rate equal to LIBOR plus 1.30% per annum, and a commitment fee on any unused portion of the SG Facility accrues at a rate equal to 0.39% per annum. Interest and commitment fees are payable quarterly.

The Credit Agreement does not include financial covenants, and the Company has not provided SG with any security for its obligations under the Credit Agreement. As described below, THUSA has entered into the Guaranty to guarantee the Company’s payment obligations to SG under the Credit Agreement. The Company has not drawn down on the SG Facility and no events of defaults had occurred as of March 31, 2019.

TOTAL Credit Support Agreement

On January 2, 2019, the Company entered a credit support agreement (“CSA”) with Total Holdings USA Inc. (“THUSA”), a wholly owned subsidiary of TOTAL (as defined in Note 15). Under the CSA, THUSA agreed to enter into a guaranty agreement (“Guaranty”) pursuant to which it has guaranteed the Company’s obligation to repay to SG up to $100,000 in Loans and interest thereon in accordance with the Credit Agreement. In consideration for the commitments of THUSA under the CSA, the Company is required to pay THUSA a quarterly guaranty fee at a rate per quarter equal to 2.5% of the average aggregate Loan amount for the preceding calendar quarter.

As security for the Company’s obligations under the CSA, on January 2, 2019, the Company entered into a pledge and security agreement with THUSA and delivered a collateral assignment of contracts to THUSA, pursuant to which the Company collaterally assigned to THUSA all fueling agreements it enters into with participants in the Zero Now truck financing program. In addition, on January 2, 2019, the Company entered into a lockbox agreement with THUSA and Plains, under which the Company granted THUSA a security interest in the cash flow generated by the fueling agreements the Company enters into with participants in the Zero Now truck financing program.

The CSA will terminate following the later of: the payment in full of all of the Company’s obligations under the CSA; and the termination or expiration of the Guaranty following the maturity date of the last outstanding Loan or December 31, 2023, whichever is earlier.

NG Advantage Debt

On May 12, 2016 and January 24, 2017, respectively, NG Advantage entered into a Loan and Security Agreement (the “Commerce LSA”) with Commerce Bank & Trust Company (“Commerce”), pursuant to which Commerce agreed to lend NG Advantage $6,300 and $6,150, respectively. The proceeds were primarily used to fund the purchases of CNG trailers and equipment. Interest and principal for both loans are payable monthly in 84 equal monthly installments at an annual rate of 4.41% and 5.0%, respectively. As collateral security for the prompt payment in full when due of NG Advantage’s obligations to Commerce under the Commerce LSA, NG Advantage pledged to and granted Commerce a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received under the Commerce LSA.

On November 30, 2016, NG Advantage entered into a Loan and Security Agreement (the “Wintrust LSA”) with Wintrust Commercial Finance (“Wintrust”), pursuant to which Wintrust agreed to lend NG Advantage $4,695. The proceeds were primarily used to fund the purchases of CNG trailers and equipment. Interest and principal is payable monthly in 72 equal monthly installments at an annual rate of 5.17%. As collateral security for the prompt payment in full when due of NG Advantage’s obligations to Wintrust under the Wintrust LSA, NG Advantage pledged to and granted Wintrust a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received under the Wintrust LSA.

Financing Obligations

NG Advantage has entered into sale and leaseback transactions with various lessors as described below. In each instance, the sale and leaseback transaction does not qualify for sale-leaseback accounting because of NG Advantage’s continuing involvement with the buyer-lessor due to a fixed price repurchase option. As a result, the transactions are recorded under the financing method, in which the assets remain on the accompanying condensed consolidated balance sheets and the proceeds from the transactions are recorded as financing liabilities.

On December 18, 2017, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “BoA MLA”) with Bank of America Leasing & Capital, LLC (“BoA”). Pursuant to the BoA MLA, NG Advantage received $2,117 in cash for CNG trailers and simultaneously leased them back from BoA for five years commencing January 1, 2018 with interest and principal payable in 60 equal monthly installments.

On March 1, 2018, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “First National MLA”) with First National Capital, LLC (“First National”). Pursuant to the First National MLA, NG Advantage received $6,261 in cash, net of fees and the first month’s lease payment for CNG trailers and simultaneously leased them back from First National for six years commencing March 1, 2018 with interest and principal payable in 72 equal monthly installments.

On December 20, 2018 (the “Closing Date”), NG Advantage entered into a purchase agreement to sell a compression station for a purchase price of $7,000 to an entity whose member owners are noncontrolling interest member owners of NG Advantage. On the Closing Date and immediately following the consummation of the sale of the compression station, NG Advantage entered into a lease agreement with the buyer of the station (the “Lease”) pursuant to which the station was leased back to NG Advantage for a term of five years with monthly rent payments equal to $70. Of the purchase price, NG Advantage received $4,730 in cash, net of fees, the first month’s lease payment, and the repayment of a $2,000 promissory note from one of the member owners of the buyer, which was issued on November 19, 2018.

On January 17, 2019, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “Nations MLA”) with Nations Fund I, LLC (“Nations”). Pursuant to the Nations MLA, NG Advantage received $3,358 in cash, net of the first month’s lease payment, for CNG trailers and simultaneously leased them back from Nations for four years commencing February 1, 2019 with interest and principal payable in 48 equal monthly installments.

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 4.78% and 4.78% as of December 31, 2018 and March 31, 2019, respectively.

Net Income (Loss) Per Share

3 Months Ended

Mar. 31, 2019

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

Basic net income (loss) per share is computed by dividing the net income (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 income (loss) per share is computed by dividing the net income (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 income (loss) per share if their effect would be antidilutive.

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



	Three Months Ended March 31,
	2018	2019
Weighted-average common shares outstanding	152,194,695	204,196,669
Dilutive effect of potential common shares from restricted stock units and stock options	4,448,397	—
Weighted-average common shares outstanding -diluted	156,643,092	204,196,669

The following potentially dilutive securities have been excluded from the diluted net income (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 March 31,
	2018	2019
Stock options	8,573,749	10,300,404
Convertible notes	14,991,521	3,164,557
Restricted stock units	—	1,305,672
Total	23,565,270	14,770,633

Stock-Based Compensation

3 Months Ended

Mar. 31, 2019

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 March 31,
	2018		2019
Stock-based compensation expense, net of $0 tax in 2018 and 2019	$	1,898	$	1,246

As of March 31, 2019, there was $5,650 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 1.97 years.

Stockholders’ Equity	3 Months Ended
Stockholders’ Equity	Mar. 31, 2019
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, in a private placement (the “Total Private Placement”). The purchase price per share was 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 March 31, 2019; (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 $1,909. 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 March 31, 2019, the Company was in compliance with all of its registration covenants set forth in the registration rights agreement.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2019
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 expense was $88 and $60 for the three months ended March 31, 2018 and 2019, respectively. Tax expense for all periods was comprised of taxes due on the Company’s U.S. and foreign operations. The decrease in the Company’s income tax expense for the three months ended March 31, 2019 as compared to the three months ended March 31, 2018 was primarily due to a reduction in the Company’s expected state tax expense. The effective tax rates for the three months ended March 31, 2018 and 2019 are different from the federal statutory tax rate primarily due to losses for which no tax benefit has been recognized. The Company increased its liability for unrecognized tax benefits in the three months ended March 31, 2018 by $2,689, which was primarily attributable to the portion of AFTC revenue recognized in the period. This 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 months ended March 31, 2018 and 2019, respectively.

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2019
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.

Leases

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

Leases

Leases (Topic 842)

On January 1, 2019, the Company adopted the new lease accounting standard (see Note 20 for more information on the standard and the impact of the adoption) where leases are now classified as either operating leases or finance leases. The Company’s operating leases are comprised of real estate for fueling stations, office spaces, warehouses, a LNG liquefaction plant, and office equipment, and its finance leases are comprised of vehicles.

At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether it obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether it has the right to direct the use of the asset. The commencement date of the contract is when the lessor makes the underlying asset available for use by the lessee.

Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made, and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less.

As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease.

The lease classification affects the expense recognition on the condensed consolidated statement of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, where depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting.

The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12.

NG Advantage has provided residual value guarantees on leases of certain vehicles aggregating $1,381 to the lessors. NG Advantage expects to owe these amounts in full and therefore they have been included in the measurement of the lease liabilities and ROU assets.

Certain of the Company’s real estate leases contain variable lease payments, including payments based on a change in the index or gasoline gallon equivalents of natural gas dispensed at fueling stations. These variable lease payments cannot be determined at the commencement of the lease, are not included in the ROU assets and liabilities and are recorded as a period expense when incurred.

Lessee Accounting

As of March 31, 2019, the Company’s finance and operating lease asset and liability balances were as follows:



	March 31, 2019
Finance leases:
Land, property and equipment, gross	$	5,299
Accumulated depreciation	(1,803		)
Land, property and equipment, net	$	3,496

Current portion of finance lease obligations	$	695
Long-term portion of finance lease obligations	3,718
Total finance lease liabilities	$	4,413

Operating leases:
Operating lease right-of-use assets ⁽¹⁾	$	23,801

Current portion of operating lease obligations	$	3,545
Long-term portion of operating lease obligations	21,621
Total operating lease liabilities	$	25,166

(1) The Company’s operating lease ROU assets are comprised of the following:



	March 31, 2019
	Assets		Liabilities
Real estate for fueling stations	$	17,370	$	17,370
LNG plant, office spaces and warehouses	6,419		7,784
Office equipment	12		12
Total operating lease right-of-use assets	$	23,801	$	25,166

The components of lease expense for finance and operating leases for three months ended March 31, 2019 consisted of the following:



	March 31, 2019
Finance leases:
Depreciation on assets under finance leases	$	259
Interest on lease liabilities	49
Total finance leases expense	$	308

Operating leases:
Lease expense	$	1,239
Lease expense on short-term leases	1,090
Variable lease expense	631
Sublease income	(52		)
Total operating leases expense	$	2,908

Supplemental information on finance and operating leases are as follows:



	March 31, 2019
Operating cash outflows from finance leases	$	(49	)
Operating cash outflows from operating leases	$	(1,224	)
Financing cash outflows from finance leases	$	(184	)

Assets obtained in exchange for new finance lease liabilities ⁽¹⁾	$	129

Weighted-average remaining lease term - finance leases	5.2 years
Weighted-average remaining lease term - operating leases	11.5 years

Weighted-average discount rate - finance leases	4.43		%
Weighted-average discount rate - operating leases	8.16		%

(1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.

The following schedule represents the Company’s maturities of finance and operating lease liabilities as of March 31, 2019:



	Finance Leases			Operating Leases
Fiscal year:
2019	$	686		$	3,839
2020	789			4,526
2021	686			3,594
2022	549			2,641
2023	529			2,629
Thereafter	1,875			22,919
Total minimum lease payments	5,114			40,148
Less amount representing interest	(701		)	(14,982		)
Present value of lease liabilities	$	4,413		$	25,166

Lessor Accounting

The Company leases fueling station equipment to customers that contain an option to extend and an end-of-term purchase option. Receivables from these leases are accounted for as finance leases, specifically sales-type leases, and are included in “Other receivables” and “Notes receivable and other long-term assets, net” in the condensed consolidated balance sheets.

The Company recognizes the net investment in the lease as the sum of the lease receivable and the unguaranteed residual value, both of which are measured at the present value using the interest rate implicit in the lease.

During the three months ended March 31, 2019, the Company recognized $37 in “Interest income” on its lease receivables.

The following schedule represents the Company’s maturities of lease receivables as of March 31, 2019:



Fiscal year:
2019	$	140
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,124
Less amount representing interest	(1,043		)
Present value of lease receivables	$	1,081

Leases (Topic 840)

As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption.

Operating Lease Commitments

The Company leases facilities, including the land for its LNG production plant in Boron, California and certain equipment under noncancelable operating leases expiring at various dates through 2038. If a lease has a fixed and determinable escalation clause, or periods of rent holidays, the difference between rental expense and rent paid is included in “Accrued liabilities” and “Other long-term liabilities” in the accompanying consolidated balance sheets.

The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018:



Fiscal year:
2019	$	6,340
2020	4,332
2021	3,311
2022	2,409
2023	2,300
Thereafter	13,214
Total future minimum lease payments	$	31,906

Rent expense, including variable rent, totaled $1,698 for the three months ended March 31, 2018.

Capital Lease Obligations and Receivables

The Company leases equipment under capital leases with a weighted-average interest rate of 4.48%. As of December 31, 2018, future payments under these capital leases are as follows:



Fiscal year:
2019	$	883
2020	742
2021	656
2022	540
2023	529
Thereafter	1,868
Total minimum lease payments	5,218
Less amount representing interest	(749		)
Capital lease obligations	4,469
Less current portion	(693		)
Capital lease obligations, less current portion	$	3,776

The value of the equipment under capital leases as of December 31, 2018 was $6,143, with related accumulated amortization of $1,832, respectively.

The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5%.

As of December 31, 2018, future receipts under this lease are as follows:



Fiscal year:
2019	$	186
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Capital lease receivables	2,170
Less amount representing interest	(1,080		)
Capital lease receivables, less current portion	$	1,090

Leases

Leases (Topic 842)

The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12.

Lessee Accounting

As of March 31, 2019, the Company’s finance and operating lease asset and liability balances were as follows:



	March 31, 2019
Finance leases:
Land, property and equipment, gross	$	5,299
Accumulated depreciation	(1,803		)
Land, property and equipment, net	$	3,496

Current portion of finance lease obligations	$	695
Long-term portion of finance lease obligations	3,718
Total finance lease liabilities	$	4,413

Operating leases:
Operating lease right-of-use assets ⁽¹⁾	$	23,801

Current portion of operating lease obligations	$	3,545
Long-term portion of operating lease obligations	21,621
Total operating lease liabilities	$	25,166

(1) The Company’s operating lease ROU assets are comprised of the following:



	March 31, 2019
	Assets		Liabilities
Real estate for fueling stations	$	17,370	$	17,370
LNG plant, office spaces and warehouses	6,419		7,784
Office equipment	12		12
Total operating lease right-of-use assets	$	23,801	$	25,166

The components of lease expense for finance and operating leases for three months ended March 31, 2019 consisted of the following:



	March 31, 2019
Finance leases:
Depreciation on assets under finance leases	$	259
Interest on lease liabilities	49
Total finance leases expense	$	308

Operating leases:
Lease expense	$	1,239
Lease expense on short-term leases	1,090
Variable lease expense	631
Sublease income	(52		)
Total operating leases expense	$	2,908

Supplemental information on finance and operating leases are as follows:



	March 31, 2019
Operating cash outflows from finance leases	$	(49	)
Operating cash outflows from operating leases	$	(1,224	)
Financing cash outflows from finance leases	$	(184	)

Assets obtained in exchange for new finance lease liabilities ⁽¹⁾	$	129

Weighted-average remaining lease term - finance leases	5.2 years
Weighted-average remaining lease term - operating leases	11.5 years

Weighted-average discount rate - finance leases	4.43		%
Weighted-average discount rate - operating leases	8.16		%

(1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.

The following schedule represents the Company’s maturities of finance and operating lease liabilities as of March 31, 2019:



	Finance Leases			Operating Leases
Fiscal year:
2019	$	686		$	3,839
2020	789			4,526
2021	686			3,594
2022	549			2,641
2023	529			2,629
Thereafter	1,875			22,919
Total minimum lease payments	5,114			40,148
Less amount representing interest	(701		)	(14,982		)
Present value of lease liabilities	$	4,413		$	25,166

Lessor Accounting

During the three months ended March 31, 2019, the Company recognized $37 in “Interest income” on its lease receivables.

The following schedule represents the Company’s maturities of lease receivables as of March 31, 2019:



Fiscal year:
2019	$	140
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,124
Less amount representing interest	(1,043		)
Present value of lease receivables	$	1,081

Leases (Topic 840)

As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption.

Operating Lease Commitments

The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018:



Fiscal year:
2019	$	6,340
2020	4,332
2021	3,311
2022	2,409
2023	2,300
Thereafter	13,214
Total future minimum lease payments	$	31,906

Rent expense, including variable rent, totaled $1,698 for the three months ended March 31, 2018.

Capital Lease Obligations and Receivables

The Company leases equipment under capital leases with a weighted-average interest rate of 4.48%. As of December 31, 2018, future payments under these capital leases are as follows:



Fiscal year:
2019	$	883
2020	742
2021	656
2022	540
2023	529
Thereafter	1,868
Total minimum lease payments	5,218
Less amount representing interest	(749		)
Capital lease obligations	4,469
Less current portion	(693		)
Capital lease obligations, less current portion	$	3,776

The value of the equipment under capital leases as of December 31, 2018 was $6,143, with related accumulated amortization of $1,832, respectively.

The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5%.

As of December 31, 2018, future receipts under this lease are as follows:



Fiscal year:
2019	$	186
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Capital lease receivables	2,170
Less amount representing interest	(1,080		)
Capital lease receivables, less current portion	$	1,090

Leases

Leases (Topic 842)

The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12.

Lessee Accounting

As of March 31, 2019, the Company’s finance and operating lease asset and liability balances were as follows:



	March 31, 2019
Finance leases:
Land, property and equipment, gross	$	5,299
Accumulated depreciation	(1,803		)
Land, property and equipment, net	$	3,496

Current portion of finance lease obligations	$	695
Long-term portion of finance lease obligations	3,718
Total finance lease liabilities	$	4,413

Operating leases:
Operating lease right-of-use assets ⁽¹⁾	$	23,801

Current portion of operating lease obligations	$	3,545
Long-term portion of operating lease obligations	21,621
Total operating lease liabilities	$	25,166

(1) The Company’s operating lease ROU assets are comprised of the following:



	March 31, 2019
	Assets		Liabilities
Real estate for fueling stations	$	17,370	$	17,370
LNG plant, office spaces and warehouses	6,419		7,784
Office equipment	12		12
Total operating lease right-of-use assets	$	23,801	$	25,166

The components of lease expense for finance and operating leases for three months ended March 31, 2019 consisted of the following:



	March 31, 2019
Finance leases:
Depreciation on assets under finance leases	$	259
Interest on lease liabilities	49
Total finance leases expense	$	308

Operating leases:
Lease expense	$	1,239
Lease expense on short-term leases	1,090
Variable lease expense	631
Sublease income	(52		)
Total operating leases expense	$	2,908

Supplemental information on finance and operating leases are as follows:



	March 31, 2019
Operating cash outflows from finance leases	$	(49	)
Operating cash outflows from operating leases	$	(1,224	)
Financing cash outflows from finance leases	$	(184	)

Assets obtained in exchange for new finance lease liabilities ⁽¹⁾	$	129

Weighted-average remaining lease term - finance leases	5.2 years
Weighted-average remaining lease term - operating leases	11.5 years

Weighted-average discount rate - finance leases	4.43		%
Weighted-average discount rate - operating leases	8.16		%

(1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.

The following schedule represents the Company’s maturities of finance and operating lease liabilities as of March 31, 2019:



	Finance Leases			Operating Leases
Fiscal year:
2019	$	686		$	3,839
2020	789			4,526
2021	686			3,594
2022	549			2,641
2023	529			2,629
Thereafter	1,875			22,919
Total minimum lease payments	5,114			40,148
Less amount representing interest	(701		)	(14,982		)
Present value of lease liabilities	$	4,413		$	25,166

Lessor Accounting

During the three months ended March 31, 2019, the Company recognized $37 in “Interest income” on its lease receivables.

The following schedule represents the Company’s maturities of lease receivables as of March 31, 2019:



Fiscal year:
2019	$	140
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,124
Less amount representing interest	(1,043		)
Present value of lease receivables	$	1,081

Leases (Topic 840)

As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption.

Operating Lease Commitments

The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018:



Fiscal year:
2019	$	6,340
2020	4,332
2021	3,311
2022	2,409
2023	2,300
Thereafter	13,214
Total future minimum lease payments	$	31,906

Rent expense, including variable rent, totaled $1,698 for the three months ended March 31, 2018.

Capital Lease Obligations and Receivables

The Company leases equipment under capital leases with a weighted-average interest rate of 4.48%. As of December 31, 2018, future payments under these capital leases are as follows:



Fiscal year:
2019	$	883
2020	742
2021	656
2022	540
2023	529
Thereafter	1,868
Total minimum lease payments	5,218
Less amount representing interest	(749		)
Capital lease obligations	4,469
Less current portion	(693		)
Capital lease obligations, less current portion	$	3,776

The value of the equipment under capital leases as of December 31, 2018 was $6,143, with related accumulated amortization of $1,832, respectively.

The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5%.

As of December 31, 2018, future receipts under this lease are as follows:



Fiscal year:
2019	$	186
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Capital lease receivables	2,170
Less amount representing interest	(1,080		)
Capital lease receivables, less current portion	$	1,090

Alternative Fuels Excise Tax Credit	3 Months Ended
Alternative Fuels Excise Tax Credit	Mar. 31, 2019
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 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 during the three months ended March 31, 2018 and was collected subsequent to that date. AFTC is not currently available, and may not be reinstated, for vehicle fuel sales made after December 31, 2017.

Recently Adopted Accounting Changes

3 Months Ended

Mar. 31, 2019

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Recently Adopted Accounting Changes

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASC 842”), which amends the guidance in former Accounting Standards Codification Topic 840, Leases (“ASC 840”). The new standard requires most leases to be recognized on the balance sheet which will increase reported assets and liabilities. Accounting for lessors and capital leases (now known as finance leases) is substantially similar to ASC 840. 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.

The Company adopted this standard using the modified retrospective method and recognized the cumulative effect of initially applying ASC 842 as an adjustment to accumulated deficit in the consolidated balance sheet as of January 1, 2019. Results for reporting periods beginning after January 1, 2019 are presented under ASC 842, while prior period amounts are not adjusted. This adoption had a material impact to the Company’s condensed consolidated balance sheets and did not have a material impact to the Company’s condensed consolidated statements of operations or its condensed consolidated statements of cash flows. The primary impact was to record ROU assets and lease liabilities for existing operating leases on the condensed consolidated balance sheets.

As permitted under ASC 842, the Company elected the package of practical expedients that permit it to not reassess (1) whether an existing contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. The Company also elected the practical expedient allowing it to use hindsight in determining the lease term and in assessing the likelihood a purchase option will be exercised.

The ASC 842 adoption adjustments are as follows:



	Balance as of December 31, 2018		Adjustments Due to ASC 842			Balance as of January 1, 2019
Operating lease right-of-use assets	$	—	$	24,453		$	24,453
Operating lease obligations	$	—	$	25,943		$	25,943
Accrued liabilities	$	48,469	$	(496	)	$	47,973
Other long-term liabilities	$	15,035	$	(994	)	$	14,041

The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of March 31, 2019 are as follows:



	March 31, 2019
	Balance before ASC 842 Adoption		Effect of Change			As Reported
Operating lease right-of-use assets	$	—	$	23,801		$	23,801
Current portion of operating lease obligations	$	—	$	3,545		$	3,545
Long-term portion of operating lease obligations	$	—	$	21,621		$	21,621
Accrued liabilities	$	37,269	$	(515	)	$	36,754
Other long-term liabilities	$	13,582	$	(850	)	$	12,732

General (Policies)

3 Months Ended

Mar. 31, 2019

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 March 31, 2019, and results of operations, comprehensive income (loss) and cash flows for the three months ended March 31, 2018 and 2019. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three month periods ended March 31, 2018 and 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 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, 2018 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 12, 2019.

Reclassifications

Certain prior period amounts have been reclassified in the condensed consolidated balance sheets and condensed consolidated statements of operations and 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, fair value measurements, goodwill and long-lived asset valuations and impairment assessments, income tax valuations and stock-based compensation expense.

Revenue Recognition Overview



	Three Months Ended March 31,
	2018		2019
Volume -related ⁽¹⁾	$	67,219	$	74,528
Station construction sales	5,798		3,170
Alternative fuels excise tax credit (“AFTC”)	25,481		—
Other	3,905		—
Total revenue	$	102,403	$	77,698

Remaining Performance Obligations

Contract Balances

As of December 31, 2018 and March 31, 2019, the Company’s contract balances were as follows:



	December 31, 2018		March 31, 2019
Receivables, net	$	68,865	$	70,341

Contract Assets - Current	$	656	$	843
Contract Assets - Noncurrent	3,825		3,740
Contract Assets - Total	$	4,481	$	4,583

Contract Liabilities - Current	$	5,513	$	5,015
Contract Liabilities - Noncurrent	9,844		6,861
Contract Liabilities - Total	$	15,357	$	11,876

Receivables, Net

Contract Assets

Contract Liabilities

Recently Adopted Accounting Changes and Recently Issued Accounting Standards

The ASC 842 adoption adjustments are as follows:



	Balance as of December 31, 2018		Adjustments Due to ASC 842			Balance as of January 1, 2019
Operating lease right-of-use assets	$	—	$	24,453		$	24,453
Operating lease obligations	$	—	$	25,943		$	25,943
Accrued liabilities	$	48,469	$	(496	)	$	47,973
Other long-term liabilities	$	15,035	$	(994	)	$	14,041

The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of March 31, 2019 are as follows:



	March 31, 2019
	Balance before ASC 842 Adoption		Effect of Change			As Reported
Operating lease right-of-use assets	$	—	$	23,801		$	23,801
Current portion of operating lease obligations	$	—	$	3,545		$	3,545
Long-term portion of operating lease obligations	$	—	$	21,621		$	21,621
Accrued liabilities	$	37,269	$	(515	)	$	36,754
Other long-term liabilities	$	13,582	$	(850	)	$	12,732

Revenue from Contracts with Customers (Tables)

3 Months Ended

Mar. 31, 2019

Revenue from Contract with Customer [Abstract]

Disaggregation of revenue



	Three Months Ended March 31,
	2018		2019
Volume -related ⁽¹⁾	$	67,219	$	74,528
Station construction sales	5,798		3,170
Alternative fuels excise tax credit (“AFTC”)	25,481		—
Other	3,905		—
Total revenue	$	102,403	$	77,698

Summary of contract balances

As of December 31, 2018 and March 31, 2019, the Company’s contract balances were as follows:



	December 31, 2018		March 31, 2019
Receivables, net	$	68,865	$	70,341

Contract Assets - Current	$	656	$	843
Contract Assets - Noncurrent	3,825		3,740
Contract Assets - Total	$	4,481	$	4,583

Contract Liabilities - Current	$	5,513	$	5,015
Contract Liabilities - Noncurrent	9,844		6,861
Contract Liabilities - Total	$	15,357	$	11,876

Cash, Cash Equivalents, and Restricted Cash (Tables)

3 Months Ended

Mar. 31, 2019

Cash and Cash Equivalents [Abstract]

Schedule of cash and cash equivalents

Cash, cash equivalents and restricted cash as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Current assets:
Cash and cash equivalents	$	29,844	$	27,983
Restricted cash - standby letter of credit	30		30
Restricted cash - held in escrow	750		750
Total cash, cash equivalents and current portion of restricted cash	$	30,624	$	28,763

Long-term assets:
Restricted cash - standby letter of credit	$	4,000	$	4,000
Restricted cash - held in escrow	—		848
Total long-term portion of restricted cash	$	4,000	$	4,848

Total cash, cash equivalents and restricted cash	$	34,624	$	33,611

Schedule of restricted cash

Cash, cash equivalents and restricted cash as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Current assets:
Cash and cash equivalents	$	29,844	$	27,983
Restricted cash - standby letter of credit	30		30
Restricted cash - held in escrow	750		750
Total cash, cash equivalents and current portion of restricted cash	$	30,624	$	28,763

Long-term assets:
Restricted cash - standby letter of credit	$	4,000	$	4,000
Restricted cash - held in escrow	—		848
Total long-term portion of restricted cash	$	4,000	$	4,848

Total cash, cash equivalents and restricted cash	$	34,624	$	33,611

Short-term Investments (Tables)

3 Months Ended

Mar. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Summary of short-term investments

Short-term investments as of December 31, 2018 consisted of the following:



	Amortized Cost		Gross Unrealized Losses			Estimated Fair Value
Municipal bonds and notes	$	9,210	$	(19	)	$	9,191
Zero coupon bonds	29,823		(28		)	29,795
Corporate bonds	26,175		(22		)	26,153
Certificates of deposit	507		—			507
Total short-term investments	$	65,715	$	(69	)	$	65,646

Short-term investments as of March 31, 2019 consisted of the following:



	Amortized Cost		Gross Unrealized Gains (Losses)			Estimated Fair Value
Municipal bonds and notes	$	20,458	$	2		$	20,460
Zero coupon bonds	23,466		(3		)	23,463
Corporate bonds	21,736		(2		)	21,734
Certificates of deposit	507		—			507
Total short-term investments	$	66,167	$	(3	)	$	66,164

Derivative Instruments and Hedging Activities (Tables)

3 Months Ended

Mar. 31, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Summary of commodity derivative activity

Commodity derivatives as of December 31, 2018 consisted of the following:



	Gross Amounts Recognized		Gross Amounts Offset		Net Amount Presented
Assets:
Current portion of derivative assets, related party	$	1,508	$	—	$	1,508
Long-term portion of derivative assets, related party	8,824		—		8,824
Total derivative assets	$	10,332	$	—	$	10,332

Commodity derivatives as of March 31, 2019 consisted of the following:



	Gross Amounts Recognized		Gross Amounts Offset		Net Amount Presented
Assets:
Current portion of derivative assets, related party	$	728	$	—	$	728
Long-term portion of derivative assets, related party	4,634		—		4,634
Total derivative assets	$	5,362	$	—	$	5,362

Schedule of weighted-average price of open commodity swap contract

The following table reflects the weighted -average price of open commodity swap contracts as of December 31, 2018 and March 31, 2019, by year with associated volumes, respectively:



	December 31, 2018			March 31, 2019
Year	Volumes (Diesel Gallons)	Weighted -Average Price per Diesel Gallon		Volumes (Diesel Gallons)	Weighted -Average Price per Diesel Gallon
2019	3,125,000	$	3.18	3,125,000	$	3.18
2020	5,000,000	$	3.18	5,000,000	$	3.18
2021	5,000,000	$	3.18	5,000,000	$	3.18
2022	5,000,000	$	3.18	5,000,000	$	3.18
2023	5,000,000	$	3.18	5,000,000	$	3.18
2024	1,875,000	$	3.18	1,875,000	$	3.18

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of fair value of outstanding commodity swap contracts

The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2018 and March 31, 2019, respectively:



	December 31, 2018			March 31, 2019
Significant Unobservable Inputs	Input Range	Weighted Average		Input Range	Weighted Average
ULSD Gulf Coast Forward Curve	$1.71 - $1.79	$	1.75	$1.90 - $1.96	$	1.93
Historical Differential to PADD 3 Diesel	$0.76 - $1.16	$	0.89	$0.76 - $1.16	$	0.89
Historical Differential to PADD 5 Diesel	$1.22 - $2.12	$	1.55	$1.25 - $2.14	$	1.59

Schedule of information by level for assets 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, 2018 and March 31, 2019, respectively:



	December 31, 2018		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities ⁽¹⁾:
Municipal bonds and notes	$	9,191	$	—	$	9,191	$	—
Zero coupon bonds	29,795		—		29,795		—
Corporate bonds	26,153		—		26,153		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	10,332		—		—		10,332
Liabilities:
Warrants ⁽³⁾	$	1,079	$	—	$	—	$	1,079



	March 31, 2019		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	20,460	$	—	$	20,460	$	—
Zero coupon bonds	23,463		—		23,463		—
Corporate bonds	21,734		—		21,734		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	5,362		—		—		5,362
Liabilities:
Warrants ⁽³⁾	$	2,693	$	—	$	—	$	2,693

(1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information.

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

Schedule of information by level for 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, 2018 and March 31, 2019, respectively:



	December 31, 2018		Level 1		Level 2		Level 3
Assets:
Available-for-sale securities ⁽¹⁾:
Municipal bonds and notes	$	9,191	$	—	$	9,191	$	—
Zero coupon bonds	29,795		—		29,795		—
Corporate bonds	26,153		—		26,153		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	10,332		—		—		10,332
Liabilities:
Warrants ⁽³⁾	$	1,079	$	—	$	—	$	1,079



	March 31, 2019		Level 1		Level 2		Level 3
Assets:
Available-for-sale debt securities ⁽¹⁾:
Municipal bonds and notes	$	20,460	$	—	$	20,460	$	—
Zero coupon bonds	23,463		—		23,463		—
Corporate bonds	21,734		—		21,734		—
Certificates of deposit ⁽¹⁾	507		—		507		—
Commodity swap contracts ⁽²⁾	5,362		—		—		5,362
Liabilities:
Warrants ⁽³⁾	$	2,693	$	—	$	—	$	2,693

(1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information.

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

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



	Assets: Commodity Swap Contracts			Liabilities: Warrants
Balance as of December 31, 2017	$	—		$	(536	)
Gain (loss) included in earnings	—			21
Balance as of March 31, 2018	$	—		$	(515	)

Balance as of December 31, 2018	$	10,332		$	(1,079	)
Gain (loss) included in earnings	(4,970		)	(1,614		)
Balance as of March 31, 2019	$	5,362		$	(2,693	)

Other Receivables (Tables)

3 Months Ended

Mar. 31, 2019

Receivables [Abstract]

Schedule of other receivables

Other receivables as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Loans to customers to finance vehicle purchases	$	276	$	1,887
Accrued customer billings	6,261		5,382
Fuel tax credits	434		434
Other	8,573		1,495
Total other receivables	$	15,544	$	9,198

Inventory (Tables)

3 Months Ended

Mar. 31, 2019

Inventory Disclosure [Abstract]

Schedule of inventories

Inventory as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Raw materials and spare parts	$	34,890	$	32,565
Finished goods	85		88
Total inventory	$	34,975	$	32,653

Land, Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2019

Property, Plant and Equipment [Abstract]

Summary of land, property and equipment

Land, property and equipment as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018			March 31, 2019
Land	$	3,681		$	3,681
LNG liquefaction plants	94,633			94,633
Station equipment	319,119			315,694
Trailers	75,901			75,221
Other equipment	97,268			97,793
Construction in progress	73,485			74,346
	664,087			661,368
Less: accumulated depreciation	(313,519		)	(323,176		)
Total land, property and equipment, net	$	350,568		$	338,192

Accrued Liabilities (Tables)

3 Months Ended

Mar. 31, 2019

Payables and Accruals [Abstract]

Schedule of accrued liabilities

Accrued liabilities as of December 31, 2018 and March 31, 2019 consisted of the following:



	December 31, 2018		March 31, 2019
Accrued alternative fuels incentives	$	6,923	$	5,969
Accrued employee benefits	2,248		2,673
Accrued interest	78		1,135
Accrued gas and equipment purchases	12,833		8,577
Accrued property and other taxes	3,397		3,001
Accrued salaries and wages	8,609		4,159
Other	14,381		11,240
Total accrued liabilities	$	48,469	$	36,754

Debt (Tables)

3 Months Ended

Mar. 31, 2019

Debt Disclosure [Abstract]

Schedule of debt obligations

Debt obligations as of December 31, 2018 and March 31, 2019 consisted of the following and are further discussed below:



	December 31, 2018
	Principal Balances			Unamortized Debt Financing Costs			Balance, Net of Financing Costs
7.5% Notes	$	50,000		$	58		$	49,942
NG Advantage debt	28,904			155			28,749
Other debt	1,024			—			1,024
Total debt	79,928			213			79,715
Less amounts due within one year	(4,811		)	(99		)	(4,712		)
Total long-term debt	$	75,117		$	114		$	75,003



	March 31, 2019
	Principal Balances			Unamortized Debt Financing Costs			Balance Net of Financing Costs
7.5% Notes	$	50,000		$	48		$	49,952
NG Advantage debt	31,065			141			30,924
Other debt	969			—			969
Total debt	82,034			189			81,845
Less amounts due within one year	(5,402		)	(58		)	(5,344		)
Total long-term debt	$	76,632		$	131		$	76,501

Net Income (Loss) Per Share (Tables)

3 Months Ended

Mar. 31, 2019

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 income (loss) per share is as follows:



	Three Months Ended March 31,
	2018	2019
Weighted-average common shares outstanding	152,194,695	204,196,669
Dilutive effect of potential common shares from restricted stock units and stock options	4,448,397	—
Weighted-average common shares outstanding -diluted	156,643,092	204,196,669

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 March 31,
	2018	2019
Stock options	8,573,749	10,300,404
Convertible notes	14,991,521	3,164,557
Restricted stock units	—	1,305,672
Total	23,565,270	14,770,633

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

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 March 31,
	2018		2019
Stock-based compensation expense, net of $0 tax in 2018 and 2019	$	1,898	$	1,246

Leases (Tables)

3 Months Ended

Mar. 31, 2019

Leases [Abstract]

Schedule of finance and operating lease asset and liability balances

As of March 31, 2019, the Company’s finance and operating lease asset and liability balances were as follows:



	March 31, 2019
Finance leases:
Land, property and equipment, gross	$	5,299
Accumulated depreciation	(1,803		)
Land, property and equipment, net	$	3,496

Current portion of finance lease obligations	$	695
Long-term portion of finance lease obligations	3,718
Total finance lease liabilities	$	4,413

Operating leases:
Operating lease right-of-use assets ⁽¹⁾	$	23,801

Current portion of operating lease obligations	$	3,545
Long-term portion of operating lease obligations	21,621
Total operating lease liabilities	$	25,166

(1) The Company’s operating lease ROU assets are comprised of the following:



	March 31, 2019
	Assets		Liabilities
Real estate for fueling stations	$	17,370	$	17,370
LNG plant, office spaces and warehouses	6,419		7,784
Office equipment	12		12
Total operating lease right-of-use assets	$	23,801	$	25,166

Schedule of omponents of lease expense for finance and operating lease liabilities and supplemental information

The components of lease expense for finance and operating leases for three months ended March 31, 2019 consisted of the following:



	March 31, 2019
Finance leases:
Depreciation on assets under finance leases	$	259
Interest on lease liabilities	49
Total finance leases expense	$	308

Operating leases:
Lease expense	$	1,239
Lease expense on short-term leases	1,090
Variable lease expense	631
Sublease income	(52		)
Total operating leases expense	$	2,908

Supplemental information on finance and operating leases are as follows:



	March 31, 2019
Operating cash outflows from finance leases	$	(49	)
Operating cash outflows from operating leases	$	(1,224	)
Financing cash outflows from finance leases	$	(184	)

Assets obtained in exchange for new finance lease liabilities ⁽¹⁾	$	129

Weighted-average remaining lease term - finance leases	5.2 years
Weighted-average remaining lease term - operating leases	11.5 years

Weighted-average discount rate - finance leases	4.43		%
Weighted-average discount rate - operating leases	8.16		%

Schedule of maturities of operating lease liabilities

The following schedule represents the Company’s maturities of finance and operating lease liabilities as of March 31, 2019:



	Finance Leases			Operating Leases
Fiscal year:
2019	$	686		$	3,839
2020	789			4,526
2021	686			3,594
2022	549			2,641
2023	529			2,629
Thereafter	1,875			22,919
Total minimum lease payments	5,114			40,148
Less amount representing interest	(701		)	(14,982		)
Present value of lease liabilities	$	4,413		$	25,166

Schedule of maturities of finance lease liabilities

The following schedule represents the Company’s maturities of finance and operating lease liabilities as of March 31, 2019:



	Finance Leases			Operating Leases
Fiscal year:
2019	$	686		$	3,839
2020	789			4,526
2021	686			3,594
2022	549			2,641
2023	529			2,629
Thereafter	1,875			22,919
Total minimum lease payments	5,114			40,148
Less amount representing interest	(701		)	(14,982		)
Present value of lease liabilities	$	4,413		$	25,166

Schedule of maturities of lease receivables

The following schedule represents the Company’s maturities of lease receivables as of March 31, 2019:



Fiscal year:
2019	$	140
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,124
Less amount representing interest	(1,043		)
Present value of lease receivables	$	1,081

Schedule of future minimum lease obligations under noncancelable operating leases

The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018:



Fiscal year:
2019	$	6,340
2020	4,332
2021	3,311
2022	2,409
2023	2,300
Thereafter	13,214
Total future minimum lease payments	$	31,906

Schedule of future payments under capital leases

The Company leases equipment under capital leases with a weighted-average interest rate of 4.48%. As of December 31, 2018, future payments under these capital leases are as follows:



Fiscal year:
2019	$	883
2020	742
2021	656
2022	540
2023	529
Thereafter	1,868
Total minimum lease payments	5,218
Less amount representing interest	(749		)
Capital lease obligations	4,469
Less current portion	(693		)
Capital lease obligations, less current portion	$	3,776

Schedule of future receipts under capital leases

As of December 31, 2018, future receipts under this lease are as follows:



Fiscal year:
2019	$	186
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Capital lease receivables	2,170
Less amount representing interest	(1,080		)
Capital lease receivables, less current portion	$	1,090

Recently Adopted Accounting Changes (Tables)

3 Months Ended

Mar. 31, 2019

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Schedule of adoption adjustments

The ASC 842 adoption adjustments are as follows:



	Balance as of December 31, 2018		Adjustments Due to ASC 842			Balance as of January 1, 2019
Operating lease right-of-use assets	$	—	$	24,453		$	24,453
Operating lease obligations	$	—	$	25,943		$	25,943
Accrued liabilities	$	48,469	$	(496	)	$	47,973
Other long-term liabilities	$	15,035	$	(994	)	$	14,041

The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of March 31, 2019 are as follows:



	March 31, 2019
	Balance before ASC 842 Adoption		Effect of Change			As Reported
Operating lease right-of-use assets	$	—	$	23,801		$	23,801
Current portion of operating lease obligations	$	—	$	3,545		$	3,545
Long-term portion of operating lease obligations	$	—	$	21,621		$	21,621
Accrued liabilities	$	37,269	$	(515	)	$	36,754
Other long-term liabilities	$	13,582	$	(850	)	$	12,732

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 77,698	$ 102,403
Loss on change in fair value of commodity swaps	(1,614)	21
Receivables, net	70,341		$ 68,865
Contract Assets - Current	843		656
Contract Assets - Noncurrent	3,740		3,825
Contract Assets - Total	4,583		4,481
Contract Liabilities - Current	5,015		5,513
Contract Liabilities - Noncurrent	6,861		9,844
Contract Liabilities - Total	11,876		$ 15,357
Volume -related
Disaggregation of Revenue [Line Items]
Revenue	74,528	67,219
Loss on change in fair value of commodity swaps	4,970	0
Station construction sales
Disaggregation of Revenue [Line Items]
Revenue	3,170	5,798
Alternative fuels excise tax credit (“AFTC”)
Disaggregation of Revenue [Line Items]
Revenue	0	25,481
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 3,905

Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue, remaining performance obligation	$ 10,494
Contract with customer, liability, revenue recognized	$ 3,317	$ 1,842

Revenue from Contracts with Customers - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01	Mar. 31, 2019
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

Investments in Other Entities and Noncontrolling Interest in a Subsidiary (Details) - USD ($)					1 Months Ended				3 Months Ended		4 Months Ended
	Apr. 15, 2019	Feb. 15, 2019	Oct. 01, 2018	Feb. 28, 2018	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Mar. 31, 2019	Mar. 31, 2018	Feb. 28, 2019	Dec. 29, 2017	Oct. 14, 2014
Acquisition and Divestitures
Loss from equity method investments									$ 467,000	$ 1,468,000
Investment balance							$ 26,079,000		25,842,000
Loss from noncontrolling interest									$ 1,879,000	1,749,000
Common unit purchase agreement \| NG Advantage
Acquisition and Divestitures
Issuance of equity by subsidiary to parent (in shares)					100,000,000	100,000,000	100,000,000	100,000			400,000
Common unit purchase agreement \| NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent			61.70%	53.50%					53.30%
Common unit purchase agreement \| NG Advantage \| NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent									64.60%
BP Products North America \| Long-Term Natural Gas Purchase Contracts \| NG Advantage
Acquisition and Divestitures
Contingent consideration, liability (up to)				$ 30,000,000
Business Combination, Contingent Consideration, Liability, Term				30 days
Clean Energy Fuels Corp. \| NG Advantage \| Convertible Debt
Acquisition and Divestitures
Debt issuance amount		$ 5,000,000
Proceeds from convertible debt		$ 2,500,000
Clean Energy Fuels Corp. \| NG Advantage \| Convertible Debt \| Subsequent Event
Acquisition and Divestitures
Proceeds from convertible debt	$ 2,500,000
SAFE&CEC S.r.l.
Acquisition and Divestitures
Ownership interest												49.00%
Loss from equity method investments									$ 440,000	1,441,000
Investment balance							$ 23,372,000		23,161,000
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									1,879,000	$ 1,749,000
Noncontrolling interest, fair value							$ 17,011,000		$ 14,904,000
NG Advantage \| Common unit purchase agreement
Acquisition and Divestitures
Ownership interest acquired													53.30%
Stock issued during period, acquisitions (in shares)			1,000,001	19,660
Payments to acquire additional controlling interest			$ 5,000,000

Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Cash and cash equivalents	$ 27,983	$ 29,844
Total cash, cash equivalents and current portion of restricted cash	28,763	30,624
Long-term portion of restricted cash	4,848	4,000
Total cash, cash equivalents and restricted cash	33,611	34,624	$ 47,096	$ 37,208
Cash in excess of insurance limits	26,658	28,524
Held in escrow
Line of Credit Facility [Line Items]
Restricted cash	750	750
Long-term portion of restricted cash	848	0
Standby letters of credit
Line of Credit Facility [Line Items]
Restricted cash	30	30
Long-term portion of restricted cash	$ 4,000	$ 4,000

Short-term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Short-term investments
Amortized Cost	$ 66,167	$ 65,715
Gross Unrealized Gains (Losses)	(3)	(69)
Estimated Fair Value	66,164	65,646
Municipal bonds and notes
Short-term investments
Amortized Cost	20,458	9,210
Gross Unrealized Gains (Losses)	2	(19)
Estimated Fair Value	20,460	9,191
Zero coupon bonds
Short-term investments
Amortized Cost	23,466	29,823
Gross Unrealized Gains (Losses)	(3)	(28)
Estimated Fair Value	23,463	29,795
Corporate bonds
Short-term investments
Amortized Cost	21,736	26,175
Gross Unrealized Gains (Losses)	(2)	(22)
Estimated Fair Value	21,734	26,153
Certificates of deposit
Short-term investments
Amortized Cost	507	507
Gross Unrealized Gains (Losses)	0	0
Estimated Fair Value	$ 507	$ 507

Derivative Instruments and Hedging Activities - Narrative (Details) - Not Designated as Hedging Instrument - Commodity swap contracts			1 Months Ended
	Mar. 31, 2019 $ / gal gal	Dec. 31, 2018 $ / gal gal	Oct. 31, 2018 contract gal
Derivative [Line Items]
Derivative asset, number of instruments held \| contract			2
Volumes (diesel gallons) \| gal	25,000,000	25,000,000	5,000,000
Weighted -average price per diesel gallon (in usd per gallon) \| $ / gal	3.18	3.18

Derivative Instruments and Hedging Activities - Summary of Commodity Derivative Activity (Details) - Not Designated as Hedging Instrument - Commodity swap contracts - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Gross Amounts Recognized	$ 5,362	$ 10,332
Gross Amounts Offset	0	0
Net Amount Presented	5,362	10,332
Current portion of derivative assets, related party
Derivative [Line Items]
Gross Amounts Recognized	728	1,508
Gross Amounts Offset	0	0
Net Amount Presented	728	1,508
Long-term portion of derivative assets, related party
Derivative [Line Items]
Gross Amounts Recognized	4,634	8,824
Gross Amounts Offset	0	0
Net Amount Presented	$ 4,634	$ 8,824

Derivative Instruments and Hedging Activities - Schedule of Weighted-Average Price of Open Commodity Wwap Contracts (Details) - Not Designated as Hedging Instrument	Mar. 31, 2019 $ / gal gal	Dec. 31, 2018 $ / gal gal
Commodity Swap 2019
Derivative [Line Items]
Volumes (diesel gallons) \| gal	3,125,000	3,125,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18
Commodity Swap 2020
Derivative [Line Items]
Volumes (diesel gallons) \| gal	5,000,000	5,000,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18
Commodity Swap 2021
Derivative [Line Items]
Volumes (diesel gallons) \| gal	5,000,000	5,000,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18
Commodity Swap 2022
Derivative [Line Items]
Volumes (diesel gallons) \| gal	5,000,000	5,000,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18
Commodity Swap 2023
Derivative [Line Items]
Volumes (diesel gallons) \| gal	5,000,000	5,000,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18
Commodity Swap 2024
Derivative [Line Items]
Volumes (diesel gallons) \| gal	1,875,000	1,875,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) \| $ / gal	3.18	3.18

Fair Value Measurements - Commodity Swap Contracts (Details) - Commodity swap contracts - Not Designated as Hedging Instrument - Valuation Technique, Discounted Cash Flow - Level 3 - member	Mar. 31, 2019	Dec. 31, 2018
Minimum \| ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.90	1.71
Minimum \| Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.76	0.76
Minimum \| Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.25	1.22
Maximum \| ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.96	1.79
Maximum \| Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.16	1.16
Maximum \| Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.14	2.12
Weighted Average \| ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.93	1.75
Weighted Average \| Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.89	0.89
Weighted Average \| Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.59	1.55

Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Available-for-sale securities	$ 66,164	$ 65,646
Short-term investments	66,164	65,646
Fair value measured on recurring basis \| Municipal bonds and notes
Assets:
Available-for-sale securities	20,460	9,191
Fair value measured on recurring basis \| Zero coupon bonds
Assets:
Available-for-sale securities	23,463	29,795
Fair value measured on recurring basis \| Corporate bonds
Assets:
Available-for-sale securities	21,734	26,153
Fair value measured on recurring basis \| Certificates of deposit
Assets:
Short-term investments	507	507
Fair value measured on recurring basis \| Commodity swap contracts
Assets:
Derivative	5,362	10,332
Fair value measured on recurring basis \| Warrants
Liabilities:
Warrants	2,693	1,079
Fair value measured on recurring basis \| Level 1 \| Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 1 \| Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 1 \| Corporate bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 1 \| Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis \| Level 1 \| Commodity swap contracts
Assets:
Derivative	0	0
Fair value measured on recurring basis \| Level 1 \| Warrants
Liabilities:
Warrants	0	0
Fair value measured on recurring basis \| Level 2 \| Municipal bonds and notes
Assets:
Available-for-sale securities	20,460	9,191
Fair value measured on recurring basis \| Level 2 \| Zero coupon bonds
Assets:
Available-for-sale securities	23,463	29,795
Fair value measured on recurring basis \| Level 2 \| Corporate bonds
Assets:
Available-for-sale securities	21,734	26,153
Fair value measured on recurring basis \| Level 2 \| Certificates of deposit
Assets:
Short-term investments	507	507
Fair value measured on recurring basis \| Level 2 \| Commodity swap contracts
Assets:
Derivative	0	0
Fair value measured on recurring basis \| Level 2 \| Warrants
Liabilities:
Warrants	0	0
Fair value measured on recurring basis \| Level 3 \| Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 3 \| Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 3 \| Corporate bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis \| Level 3 \| Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis \| Level 3 \| Commodity swap contracts
Assets:
Derivative	5,362	10,332
Fair value measured on recurring basis \| Level 3 \| Warrants
Liabilities:
Warrants	$ 2,693	$ 1,079

Fair Value Measurements - Fair Value Recognition - Assets (Details) - Commodity Swap Contracts - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	$ 10,332	$ 0
Gain (loss) included in earnings	(4,970)	0
Ending balance	$ 5,362	$ 0

Fair Value Measurements - Fair Value Recognition - Liabilities (Details) - Warrants - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance	$ (1,079)	$ (536)
Gain (loss) included in earnings	(1,614)	21
Ending Balance	$ (2,693)	$ (515)

Other Receivables (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Other Receivables
Other receivables	$ 9,198	$ 15,544
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	1,887	276
Accrued customer billings
Other Receivables
Other receivables	5,382	6,261
Fuel tax credits
Other Receivables
Other receivables	434	434
Other
Other Receivables
Other receivables	$ 1,495	$ 8,573

Inventory (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials and spare parts	$ 32,565	$ 34,890
Finished goods	88	85
Total inventory	$ 32,653	$ 34,975

Land, Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Land, Property and Equipment
Land, property and equipment, gross	$ 661,368		$ 664,087
Less: accumulated depreciation	(323,176)		(313,519)
Total land, property and equipment, net	338,192		350,568
Capitalized software costs	29,573		29,344
Accumulated amortization on the capitalized software costs	23,504		22,472
Amortization expense related to the capitalized software costs	1,035	$ 718
Property and equipment purchases included in accounts payable and accrued liabilities	2,163		939
Land
Land, Property and Equipment
Land, property and equipment, gross	3,681		3,681
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,633		94,633
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	315,694		319,119
Trailers
Land, Property and Equipment
Land, property and equipment, gross	75,221		75,901
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	97,793		97,268
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 74,346		$ 73,485

Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 5,969		$ 6,923
Accrued employee benefits	2,673		2,248
Accrued interest	1,135		78
Accrued gas and equipment purchases	8,577		12,833
Accrued property and other taxes	3,001		3,397
Accrued salaries and wages	4,159		8,609
Other	11,240		14,381
Total accrued liabilities	$ 36,754	$ 47,973	$ 48,469

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2013	Jul. 11, 2011
Principal Balances
Total debt	$ 82,034	$ 79,928
Less amounts due within one year	(5,402)	(4,811)
Total long-term debt	76,632	75,117
Unamortized Debt Financing Costs
Total debt	189	213
Less amounts due within one year	(58)	(99)
Total long-term debt	131	114
Balance, Net of Financing Costs
Total debt	81,845	79,715
Less amounts due within one year	(5,344)	(4,712)
Total long-term debt	76,501	75,003
7.5% Notes
Principal Balances
Total debt	50,000	50,000
Unamortized Debt Financing Costs
Total debt	48	58
Balance, Net of Financing Costs
Total debt	$ 49,952	49,942
Interest rate	7.50%		7.50%	7.50%
NG Advantage debt
Principal Balances
Total debt	$ 31,065	28,904
Unamortized Debt Financing Costs
Total debt	141	155
Balance, Net of Financing Costs
Total debt	30,924	28,749
Other debt
Principal Balances
Total debt	969	1,024
Unamortized Debt Financing Costs
Total debt	0	0
Balance, Net of Financing Costs
Total debt	$ 969	$ 1,024

Debt - 7.5% Notes (Details)			1 Months Ended	55 Months Ended
Debt - 7.5% Notes (Details)	Dec. 04, 2018 USD ($)	Jun. 29, 2018 USD ($)	Jun. 30, 2013 USD ($) day $ / shares shares	Dec. 31, 2017 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 11, 2011
Long-term debt [Line Items]
Aggregate principal amount					$ 82,034,000	$ 79,928,000
7.5% Notes
Long-term debt [Line Items]
Interest rate			7.50%		7.50%		7.50%
Debt issuance amount			$ 150,000,000
Debt instrument, repurchase amount during period	$ 50,000,000
Payments for repurchase and retirement of debt instrument	$ 50,500,000
Aggregate principal amount					$ 50,000,000	$ 50,000,000
7.5% Notes \| Buyers
Long-term debt [Line Items]
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
7.5% Notes \| Green Energy Investment Holdings, LLC
Long-term debt [Line Items]
Debt instrument, repurchase amount during period		$ 25,000,000
Principal amount transferred				$ 16,800,000
Payment of accrued and unpaid interest		$ 505,000
Aggregate principal amount					32,906,000
7.5% Notes \| Green Energy Investment Holdings, LLC \| Boone Pickens
Long-term debt [Line Items]
Debt instrument, repurchase amount during period				$ 25,000,000
7.5% Notes \| Other Third Parties
Long-term debt [Line Items]
Aggregate principal amount					$ 17,094,000

Debt - Plains Credit Facility (Details) - Plains Credit Facility - USD ($)	Feb. 29, 2016	Mar. 31, 2019
Long-term debt [Line Items]
Line of credit limit	$ 50,000,000
Line of credit		$ 0
Interest rate	2.70%
LIBOR
Long-term debt [Line Items]
Basis spread on variable rate	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 - Société Générale Term Loan Facility (Details) - Line of Credit - Société Générale - Term Loan Facility	Jan. 02, 2019 USD ($)
Line of Credit Facility [Line Items]
Line of credit limit	$ 100,000,000
Unused capacity, commitment fee percentage	0.39%
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.30%

Debt - TOTAL Credit Support Agreement (Details) - Total Holdings USA Inc. - Credit Support Agreement	Jan. 02, 2019 USD ($)
Long-term debt [Line Items]
Debt issuance amount	$ 100,000,000
Guaranty fee percentage	2.50%

Debt - NG Advantage Debt (Details)	Jan. 17, 2019 USD ($) installment	Dec. 20, 2018 USD ($)	Mar. 01, 2018 USD ($) installment	Dec. 18, 2017 USD ($) installment	Jan. 24, 2017 USD ($)	Nov. 30, 2016 USD ($) installment	May 12, 2016 USD ($) installment
Commerce Bank & Trust Company \| Loan And Security Agreement \| 4.41% Term Loan
Long-term debt [Line Items]
Debt issuance amount							$ 6,300,000
Number of equal monthly installments \| installment							84
Interest rate							4.41%
Commerce Bank & Trust Company \| Loan And Security Agreement \| 5.0% Term Loan
Long-term debt [Line Items]
Debt issuance amount					$ 6,150,000
Number of equal monthly installments \| installment							84
Interest rate					5.00%
Wintrust Commercial Finance \| Loan And Security Agreement \| 5.17% Term Loan
Long-term debt [Line Items]
Debt issuance amount						$ 4,695,000
Number of equal monthly installments \| installment						72
Interest rate						5.17%
Master Lease Agreement \| Bank Of America Leasing & Capital, LLC
Long-term debt [Line Items]
Gross proceeds, financing activities				$ 2,117,000
Term of agreement				5 years
Number of equal monthly installments \| installment				60
Master Lease Agreement \| First National Capital, LLC
Long-term debt [Line Items]
Net proceeds, financing activities			$ 6,261,000
Term of agreement			6 years
Number of equal monthly installments \| installment			72
Master Lease Agreement \| Nations Fund I, LLC
Long-term debt [Line Items]
Net proceeds, financing activities	$ 3,358,000
Term of agreement	4 years
Number of equal monthly installments \| installment	48
NG Advantage Financing Lease Obligation
Long-term debt [Line Items]
Net proceeds, financing activities		$ 4,730,000
Term of agreement		5 years
Purchase price		$ 7,000,000
Monthly rental payments		70,000
Rent expense, repayment of promissory note		$ 2,000,000

Debt - Other Debt (Details) - Other Debt	Mar. 31, 2019	Dec. 31, 2018
Long-term debt [Line Items]
Weighted average interest rate	4.78%	4.78%
Maximum
Long-term debt [Line Items]
Interest rate	5.02%

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Weighted-average common shares outstanding (in shares)	204,196,669	152,194,695
Dilutive effect of potential common shares from restricted stock units and stock options (in shares)	0	4,448,397
Weighted-average common shares outstanding - diluted (in shares)	204,196,669	156,643,092

Net Income (Loss) Per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Loss Per Share
Anti-dilutive securities (in shares)	14,770,633	23,565,270
Stock Options
Net Loss Per Share
Anti-dilutive securities (in shares)	10,300,404	8,573,749
Convertible Notes
Net Loss Per Share
Anti-dilutive securities (in shares)	3,164,557	14,991,521
Restricted stock units
Net Loss Per Share
Anti-dilutive securities (in shares)	1,305,672	0

Stock-Based Compensation (Details) - USD ($)	3 Months Ended
Stock-Based Compensation (Details) - USD ($)	Mar. 31, 2019	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense, net of $0 tax in 2018 and 2019	$ 1,246,000	$ 1,898,000
Stock-based compensation expense, tax	0	$ 0
Unrecognized compensation cost	$ 5,650,000
Unrecognized compensation cost, weighted-average period	1 year 11 months 19 days

Stockholders’ Equity (Details) - Purchase Agreement - USD ($) $ / shares in Units, $ in Thousands	Jun. 13, 2018	May 09, 2018
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	$ 1,909
Purchase Percentage Covenant, Threshold
Subsidiary, Sale of Stock [Line Items]
Percentage of ownership after transaction		5.00%
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
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense	$ 60	$ 88
Unrecognized tax benefits, increase from portion of AFTC revenue offset by the fuel tax		$ 2,689

Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
Leases - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Residual value of leased asset	$ 1,381
Sales-type lease, interest income	37
Operating leases, rent expense, including variable rent		$ 1,698
Capital leases weighted average interest rate			4.48%
Capital leased assets, gross			$ 6,143
Capital leases, accumulated depreciation			$ 1,832
Capital leases, sales type leases, interest rate			13.50%
T. Boone Pickens
Lessee, Lease, Description [Line Items]
Lessee, operating lease, monthly rental payments	$ 12

Leases - Finance and Operating Lease Asset and Liability Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Finance leases:
Land, property and equipment, gross	$ 5,299
Accumulated depreciation	(1,803)
Land, property and equipment, net	3,496
Current portion of finance lease obligations	695
Long-term portion of finance lease obligations	3,718
Total finance lease liabilities	4,413
Operating leases:
Operating lease right-of-use assets	23,801	$ 24,453
Current portion of operating lease obligations	3,545
Long-term portion of operating lease obligations	21,621
Total operating lease liabilities	25,166	$ 25,943
Real estate for fueling stations
Operating leases:
Operating lease right-of-use assets	17,370
Total operating lease liabilities	17,370
LNG plant, office spaces and warehouses
Operating leases:
Operating lease right-of-use assets	6,419
Total operating lease liabilities	7,784
Office equipment
Operating leases:
Operating lease right-of-use assets	12
Total operating lease liabilities	$ 12

Leases - Components of Lease Expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Finance leases:
Depreciation on assets under finance leases	$ 259
Interest on lease liabilities	49
Total finance leases expense	308
Operating leases:
Lease expense	1,239
Lease expense on short-term leases	1,090
Variable lease expense	631
Sublease income	(52)
Total operating leases expense	$ 2,908

Leases - Supplemental Information (Details) $ in Thousands	3 Months Ended
Leases - Supplemental Information (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating cash outflows from finance leases	$ (49)
Operating cash outflows from operating leases	(1,224)
Financing cash outflows from finance leases	(184)
Assets obtained in exchange for new finance lease liabilities	$ 129
Weighted-average remaining lease term - finance leases	5 years 2 months 16 days
Weighted-average remaining lease term - operating leases	11 years 6 months 7 days
Weighted-average discount rate - finance leases	4.43%
Weighted-average discount rate - operating leases	8.16%

Leases - Maturities of Finance and Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Finance Leases
2019	$ 686
2020	789
2021	686
2022	549
2023	529
Thereafter	1,875
Total minimum lease payments	5,114
Less amount representing interest	(701)
Present value of lease liabilities	4,413
Operating Leases
2019	3,839
2020	4,526
2021	3,594
2022	2,641
2023	2,629
Thereafter	22,919
Total minimum lease payments	40,148
Less amount representing interest	(14,982)
Present value of lease liabilities	$ 25,166	$ 25,943

Leases - Maturities of Lease Receivables (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Fiscal year:
2019	$ 140
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,124
Less amount representing interest	(1,043)
Present value of lease receivables	$ 1,081

Leases - Operating Lease Commitments (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Fiscal year:
2019	$ 6,340
2020	4,332
2021	3,311
2022	2,409
2023	2,300
Thereafter	13,214
Total future minimum lease payments	$ 31,906

Leases - Capitalized Lease Obligation (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Fiscal year:
2019	$ 883
2020	742
2021	656
2022	540
2023	529
Thereafter	1,868
Total minimum lease payments	5,218
Less amount representing interest	(749)
Capital lease obligations	4,469
Less current portion	(693)
Capital lease obligations, less current portion	$ 3,776

Leases - Capitalized Lease Receivables (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Fiscal year:
2019	$ 186
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Capital lease receivables	2,170
Less amount representing interest	(1,080)
Capital lease receivables, less current portion	$ 1,090

Alternative Fuels Excise Tax Credit (Details) $ in Thousands	12 Months Ended			14 Months Ended
	Dec. 31, 2017 $ / gallon	Dec. 31, 2016 $ / gallon	Dec. 31, 2015 $ / gallon	Mar. 31, 2019 USD ($)
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
Federal alternative fuels tax credit - credits recognized as revenue \| $				$ 25,481

Recently Adopted Accounting Changes (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 23,801	$ 24,453
Operating lease obligations	25,166	25,943
Accrued liabilities	36,754	47,973	$ 48,469
Other long-term liabilities	12,732	14,041	$ 15,035
Current portion of operating lease obligations	3,545
Long-term portion of operating lease obligations	21,621
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		24,453
Operating lease obligations		25,943
Accrued liabilities		(496)
Other long-term liabilities		$ (994)
Balance before ASC 842 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accrued liabilities	37,269
Other long-term liabilities	13,582
Effect of Change \| Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	23,801
Accrued liabilities	(515)
Other long-term liabilities	(850)
Current portion of operating lease obligations	3,545
Long-term portion of operating lease obligations	$ 21,621

Label	Element	Value
Noncontrolling Interest [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	$ 22,668,000
Common Stock [Member]
Common Stock, Shares, Issued	us-gaap_CommonStockSharesIssued	151,650,969
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	$ 15,000
Additional Paid-in Capital [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	1,111,432,000
AOCI Attributable to Parent [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(887,000)
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(684,863,000)
Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	(1,293,000)
Accounting Standards Update 2014-09 [Member] \| Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (1,293,000)