Clean Energy Fuels (CLNE) 10-Q 5 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
Entity File Number	001-33480
Entity Registrant Name	CLEAN ENERGY FUELS CORP.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0968580
Entity Address, Address Line One	4675 MacArthur Court, Suite 800
Entity Address, City or Town	Newport Beach
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92660
City Area Code	949
Local Phone Number	437-1000
Title of 12(b) Security	Common stock
Trading Symbol	CLNE
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		198,270,294
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001368265
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash, cash equivalents and current portion of restricted cash	$ 91,605	$ 49,222
Short-term investments	530	56,929
Accounts receivable, net of allowance of $2,412 and $1,931 as of December 31, 2019 and September 30, 2020, respectively	52,904	61,760
Other receivables	23,152	84,898
Inventory	28,830	29,874
Prepaid expenses and other current assets	8,492	11,109
Derivative assets, related party	3,269
Total current assets	208,782	293,792
Operating lease right-of-use assets	26,567	28,627
Land, property and equipment, net	298,088	323,912
Long-term portion of restricted cash	4,000	4,000
Notes receivable and other long-term assets, net	28,453	31,622
Long-term portion of derivative assets, related party	6,570	3,270
Investments in other entities	25,985	26,305
Goodwill	64,328	64,328
Intangible assets, net	627	1,229
Total assets	663,400	777,085
Current liabilities:
Current portion of debt	6,126	56,013
Current portion of finance lease obligations	964	615
Current portion of operating lease obligations	3,189	3,359
Accounts payable	17,081	27,376
Accrued liabilities	50,202	67,697
Deferred revenue	1,720	7,338
Derivative liabilities, related party		164
Total current liabilities	79,282	162,562
Long-term portion of debt	29,047	32,872
Long-term portion of finance lease obligations	2,727	2,715
Long-term portion of operating lease obligations	24,008	26,206
Other long-term liabilities	4,867	9,701
Total liabilities	139,931	234,056
Commitments and contingencies (Note 17)
Stockholders' equity:
Preferred stock, $0.0001 par value. 1,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value. 304,000,000 shares authorized; 204,723,055 shares and 198,412,898 shares issued and outstanding as of December 31, 2019 and September 30, 2020, respectively	20	20
Additional paid-in capital	1,191,140	1,203,186
Accumulated deficit	(675,535)	(668,232)
Accumulated other comprehensive loss	(1,791)	(1,566)
Total Clean Energy Fuels Corp. stockholders' equity	513,834	533,408
Noncontrolling interest in subsidiary	9,635	9,621
Total stockholders' equity	523,469	543,029
Total liabilities and stockholders' equity	$ 663,400	$ 777,085

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,931	$ 2,412
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)	198,412,898	204,723,055
Common stock, outstanding (in shares)	198,412,898	204,723,055

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues [Abstract]
Total revenue	$ 70,886	$ 74,434	$ 216,766	$ 224,450
Cost of sales (exclusive of depreciation and amortization shown separately below):
Change in fair value of derivative warrants		(10)	(40)	1,587
Selling, general and administrative	16,639	17,640	51,790	54,007
Depreciation and amortization	11,744	12,247	35,718	37,331
Total operating expenses	73,672	79,809	224,242	249,295
Operating loss	(2,786)	(5,375)	(7,476)	(24,845)
Interest expense	(1,009)	(1,704)	(5,060)	(5,437)
Interest income	427	560	1,081	1,707
Other income, net	919	165	3,381	2,928
Income (loss) from equity method investments	(11)	377	(368)	(123)
Loss before income taxes	(2,460)	(5,977)	(8,442)	(25,770)
Income tax expense	(79)	(68)	(235)	(194)
Net Loss	(2,539)	(6,045)	(8,677)	(25,964)
Loss attributable to noncontrolling interest	268	1,711	1,374	5,301
Net loss attributable to Clean Energy Fuels Corp.	$ (2,271)	$ (4,334)	$ (7,303)	$ (20,663)
Net loss attributable to Clean Energy Fuels Corp. per share:
Basic and diluted (in dollars per share)	$ (0.01)	$ (0.02)	$ (0.04)	$ (0.10)
Weighted-average common shares outstanding:
Basic and diluted (in shares)	198,785,394	204,712,888	201,472,851	204,522,984
Product revenue
Revenues [Abstract]
Total revenue	$ 60,310	$ 62,808	$ 186,438	$ 190,947
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	38,767	43,145	118,494	137,696
Service revenue
Revenues [Abstract]
Total revenue	10,576	11,626	30,328	33,503
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	$ 6,522	$ 6,787	$ 18,280	$ 18,674

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Loss	$ (2,539)	$ (6,045)	$ (8,677)	$ (25,964)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of $0 tax in 2019 and 2020	687	(623)	(227)	7
Unrealized gains (losses) on available-for-sale securities, net of $0 tax in 2019 and 2020	(3)	5	2	73
Total other comprehensive income (loss)	684	(618)	(225)	80
Comprehensive loss	(1,855)	(6,663)	(8,902)	(25,884)
Clean Energy Fuels Corp.
Net Loss	(2,271)	(4,334)	(7,303)	(20,663)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of $0 tax in 2019 and 2020	687	(623)	(227)	7
Unrealized gains (losses) on available-for-sale securities, net of $0 tax in 2019 and 2020	(3)	5	2	73
Total other comprehensive income (loss)	684	(618)	(225)	80
Comprehensive loss	(1,587)	(4,952)	(7,528)	(20,583)
Noncontrolling Interest in Subsidiary
Net Loss	(268)	(1,711)	(1,374)	(5,301)
Other comprehensive income (loss), net of tax:
Comprehensive loss	$ (268)	$ (1,711)	$ (1,374)	$ (5,301)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustment, tax	$ 0	$ 0	$ 0	$ 0
Unrealized gains on available-for sale securities, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiary	Total
Beginning balance at Dec. 31, 2018	$ 20	$ 1,198,769	$ (688,653)	$ (2,138)	$ 17,011	$ 525,009
Beginning balance (in shares) at Dec. 31, 2018	203,599,892
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		175				175
Issuance of common stock (in shares)	1,052,040
Stock-based compensation		1,246				1,246
Net income (loss)			(10,946)		(1,879)	(12,825)
Other comprehensive income (loss)				374		374
Increase in ownership in subsidiary		228			(228)
Ending balance at Mar. 31, 2019	$ 20	1,200,418	(699,599)	(1,764)	14,904	513,979
Ending balance (in shares) at Mar. 31, 2019	204,651,932
Beginning balance at Dec. 31, 2018	$ 20	1,198,769	(688,653)	(2,138)	17,011	525,009
Beginning balance (in shares) at Dec. 31, 2018	203,599,892
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(5,301)	(25,964)
Other comprehensive income (loss)						80
Ending balance at Sep. 30, 2019	$ 20	1,202,339	(709,316)	(2,058)	11,482	502,467
Ending balance (in shares) at Sep. 30, 2019	204,719,995
Beginning balance at Mar. 31, 2019	$ 20	1,200,418	(699,599)	(1,764)	14,904	513,979
Beginning balance (in shares) at Mar. 31, 2019	204,651,932
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		4				4
Issuance of common stock (in shares)	3,214
Stock-based compensation		918				918
Net income (loss)			(5,383)		(1,711)	(7,094)
Other comprehensive income (loss)				324		324
Ending balance at Jun. 30, 2019	$ 20	1,201,340	(704,982)	(1,440)	13,193	508,131
Ending balance (in shares) at Jun. 30, 2019	204,655,146
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		107				107
Issuance of common stock (in shares)	64,849
Stock-based compensation		892				892
Net income (loss)			(4,334)		(1,711)	(6,045)
Other comprehensive income (loss)				(618)		(618)
Ending balance at Sep. 30, 2019	$ 20	1,202,339	(709,316)	(2,058)	11,482	502,467
Ending balance (in shares) at Sep. 30, 2019	204,719,995
Beginning balance at Dec. 31, 2019	$ 20	1,203,186	(668,232)	(1,566)	9,621	$ 543,029
Beginning balance (in shares) at Dec. 31, 2019	204,723,055					204,723,055
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		194				$ 194
Issuance of common stock (in shares)	871,010
Repurchase of common stock		(4,244)				(4,244)
Repurchase of common stock (in shares)	(2,810,449)
Stock-based compensation		1,054				1,054
Net income (loss)			1,704		(805)	899
Other comprehensive income (loss)				(1,915)		(1,915)
Increase in ownership in subsidiary		(1,388)			1,388
Ending balance at Mar. 31, 2020	$ 20	1,198,802	(666,528)	(3,481)	10,204	539,017
Ending balance (in shares) at Mar. 31, 2020	202,783,616
Beginning balance at Dec. 31, 2019	$ 20	1,203,186	(668,232)	(1,566)	9,621	$ 543,029
Beginning balance (in shares) at Dec. 31, 2019	204,723,055					204,723,055
Increase (Decrease) in Stockholders' Equity
Repurchase of common stock						$ (13,500)
Repurchase of common stock (in shares)						(7,347,691)
Net income (loss)					(1,374)	$ (8,677)
Other comprehensive income (loss)						(225)
Ending balance at Sep. 30, 2020	$ 20	1,191,140	(675,535)	(1,791)	9,635	$ 523,469
Ending balance (in shares) at Sep. 30, 2020	198,412,898					198,412,898
Beginning balance at Mar. 31, 2020	$ 20	1,198,802	(666,528)	(3,481)	10,204	$ 539,017
Beginning balance (in shares) at Mar. 31, 2020	202,783,616
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		41				41
Issuance of common stock (in shares)	25,214
Repurchase of common stock		(6,406)				(6,406)
Repurchase of common stock (in shares)	(3,302,050)
Stock-based compensation		760				760
Net income (loss)			(6,736)		(301)	(7,037)
Other comprehensive income (loss)				1,006		1,006
Ending balance at Jun. 30, 2020	$ 20	1,193,197	(673,264)	(2,475)	9,903	527,381
Ending balance (in shares) at Jun. 30, 2020	199,506,780
Increase (Decrease) in Stockholders' Equity
Issuance of common stock		248				248
Issuance of common stock (in shares)	141,310
Repurchase of common stock		(3,013)				(3,013)
Repurchase of common stock (in shares)	(1,235,192)
Stock-based compensation		708				708
Net income (loss)			(2,271)		(268)	(2,539)
Other comprehensive income (loss)				684		684
Ending balance at Sep. 30, 2020	$ 20	$ 1,191,140	$ (675,535)	$ (1,791)	$ 9,635	$ 523,469
Ending balance (in shares) at Sep. 30, 2020	198,412,898					198,412,898

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net Loss	$ (8,677)	$ (25,964)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	35,718	37,331
Provision for credit losses and inventory	1,421	1,071
Stock-based compensation expense	2,522	3,056
Change in fair value of derivative instruments	(4,055)	4,854
Derivative settlement loss		(210)
Amortization of discount and debt issuance cost	(69)	(555)
Gain on disposal of property and equipment	(3,314)	(4,043)
Gain from sale of certain assets of subsidiary	(176)
Loss from equity method investments	368	123
Non-cash lease expense	2,060	2,597
Deferred income taxes	90
Changes in operating assets and liabilities, net of assets and liabilities acquired and disposed:
Accounts and other receivables	62,602	3,947
Inventory	437	2,799
Prepaid expenses and other assets	4,626	(4,593)
Operating lease liabilities	(2,368)	(3,053)
Accounts payable	(8,630)	(3,215)
Deferred revenue	(11,957)	(3,121)
Accrued liabilities and other	(17,476)	(6,421)
Net cash provided by operating activities	53,122	4,603
Cash flows from investing activities:
Purchases of short-term investments	(45,293)	(138,260)
Maturities and sales of short-term investments	101,850	137,896
Purchases of and deposits on property and equipment	(9,985)	(12,252)
Loans made to customers	(40)
Payments on and proceeds from sales of loans receivable	1,442	556
Cash received from sale of certain assets of subsidiary, net	4,830	4,973
Investments in other entities	(150)
Proceeds from disposal of property and equipment	4,615	6,569
Net cash provided by (used in) investing activities	57,269	(518)
Cash flows from financing activities:
Issuances of common stock	483	286
Repurchase of common stock	(13,663)
Proceeds from debt instruments	300	3,694
Repayments of debt instruments and finance lease obligations	(55,009)	(5,066)
Fees paid for debt issuance costs		(29)
Net cash used in financing activities	(67,889)	(1,115)
Effect of exchange rates on cash, cash equivalents, and restricted cash	(119)	109
Net increase in cash, cash equivalents and restricted cash	42,383	3,079
Cash, cash equivalents and restricted cash, beginning of period	53,222	34,624
Cash, cash equivalents and restricted cash, end of period	95,605	37,703
Supplemental disclosure of cash flow information:
Income taxes paid	46	36
Interest paid, net of $391 and $57 capitalized, respectively	$ 4,841	$ 4,913

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Statement of Cash Flows [Abstract]
Interest paid, capitalized	$ 57	$ 391

General

General	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	Clean Energy Fuels Corp. and Subsidiaries Notes to Condensed Consolidated Financial Statements (Unaudited) Note 1—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 renewable and conventional natural gas as alternative fuels for vehicle fleets and related 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 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 September 30, 2020, results of operations, comprehensive loss, and stockholders’ equity for the three and nine months ended September 30, 2019 and 2020, and cash flows for the nine months ended September 30, 2019 and 2020. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and nine month periods ended September 30, 2019 and 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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 (“U.S. 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, 2019 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 10, 2020. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. 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. ​ Recently Adopted Accounting Pronouncements ​ In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ​ Recently Issued Accounting Pronouncements Pending Adoption ​ In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ​

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Note 2—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 Company is generally the principal in its customer contracts because it has control over the goods and services prior to transfer 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. The table below presents the Company’s revenue disaggregated by revenue source (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Volume-related (1) ​ $ 67,869 ​ $ 57,127 ​ $ 208,667 ​ $ 182,417 Station construction sales ​ 6,431 ​ 8,743 ​ 15,544 ​ 19,543 AFTC (2) ​ — ​ 5,016 ​ — ​ 14,806 Other ​ 134 ​ — ​ 239 ​ — Total revenue ​ $ 74,434 ​ $ 70,886 ​ $ 224,450 ​ $ 216,766 (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts associated with the Company’s Zero Now truck financing program. 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 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 and nine months ended September 30, 2019, changes in the fair value of commodity swaps and customer fueling contracts amounted to a gain of $1.1 million and a loss of $3.3 million, respectively. For the three and nine months ended September 30, 2020, changes in the fair value of commodity swaps and customer fueling contracts amounted to a loss of $0.1 million and a gain of $4.0 million, respectively. (2) Represents the federal alternative fuel excise tax credit that we refer to as “AFTC,” which had previously expired but on December 20, 2019 was retroactively extended for vehicle fuel sales made beginning January 1, 2018 through December 31, 2020. See Note 19 for more information. Remaining Performance Obligations Remaining performance obligations represent the transaction price of customer orders for which the work has not been performed. As of September 30, 2020, the aggregate amount of the transaction price allocated to remaining performance obligations was $15.2 million, 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 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 ‘ 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. As of December 31, 2019 and September 30, 2020, the Company’s contract balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Accounts receivable, net ​ $ 61,760 ​ $ 52,904 ​ ​ ​ ​ ​ Contract assets - current ​ $ 455 ​ $ 955 Contract assets - non-current ​ 3,777 ​ 3,854 Contract assets - total ​ $ 4,232 ​ $ 4,809 ​ ​ ​ ​ ​ Contract liabilities - current ​ $ 5,329 ​ $ 938 Contract liabilities - non-current ​ 6,339 ​ — Contract liabilities - total ​ $ 11,668 ​ $ 938 ​ Accounts Receivable, Net "Accounts receivable, net" in the accompanying condensed consolidated balance sheets includes amounts billed and currently due from customers. The amounts due are stated at their net estimated realizable value. The Company maintains an allowance 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, the age of outstanding receivables, and economic conditions that may affect a customer’s ability to pay. 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 and are classified as current or noncurrent based on when the related revenue is expected to be recognized. The current portion and noncurrent portion of contract liabilities are included in “Deferred revenue” and “Other long-term liabilities,” respectively, in the accompanying condensed consolidated balance sheets. Revenue recognized during the nine months ended September 30, 2019 related to the Company’s contract liability balances as of December 31, 2018 was $4.4 million. Revenue recognized during the nine months ended September 30, 2020 related to the Company’s contract liability balances as of December 31, 2019 was $4.8 million. In June 2020, the Company entered into a termination letter between NG Advantage and BP (as defined in Note 3) and paid $7.8 million in satisfaction of the remaining performance obligations, resulting in a reduction of the Company’s contract liability balance as of December 31, 2019 of $7.0 million, and a net revenue impact of $(0.8) million. Contract liabilities increased during the nine months ended September 30, 2020 as a result of billings in excess of revenue recognized and advance payments received from customers.

Investments in Other Entities a

Investments in Other Entities and Noncontrolling Interest in a Subsidiary	9 Months Ended
	Sep. 30, 2020
Investments, All Other Investments [Abstract]
Investments in Other Entities and Noncontrolling Interest in a Subsidiary	Note 3— 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 fueling systems manufacturing subsidiaries, CEC and SAFE S.p.A, in a new company, 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. As of 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 SAFE&CEC S.r.l., but has the ability to exercise significant influence over SAFE&CEC S.r.l.’s operations. The Company recorded income of $0.4 million and $0.0 million from this investment for the three months ended September 30, 2019 and 2020, respectively, and a loss of $0.0 million and $0.4 million for the nine months ended September 30, 2019 and 2020, respectively. The Company had an investment balance in SAFE&CEC S.r.l. of $23.7 million and $23.2 million as of December 31, 2019 and September 30, 2020, 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. In June 2020, the Company paid BP $7.8 million to terminate a portion of the forgoing arrangement. In connection with the arrangement, 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 $30.0 million plus related fees, which was reduced to $15.0 million effective June 24, 2020. This guaranty is in effect until thirty days following the Company’s notice to BP of its termination. As of December 31, 2019, NG Advantage had an outstanding balance of $26.7 million, plus accrued and unpaid interest, under the delayed draw convertible promissory note entered into with the Company in November 2019 (the “November 2019 Convertible Note”). On February 6, 2020, the Company converted the outstanding principal and accrued interest under the November 2019 Convertible Note into common units of NG Advantage, resulting in an increase in the Company’s controlling interest in NG Advantage from 64.6% to 93.2%. On February 29, 2020, NG Advantage issued to the Company 283,019 common units pursuant to the guaranty agreement entered in February 2018, which increased the Company’s controlling interest in NG Advantage to 93.3% as of September 30, 2020. The Company recorded a loss attributable to the noncontrolling interest in NG Advantage of $1.7 million and $0.3 million for the three months ended September 30, 2019 and 2020, respectively, and $5.3 million and $1.4 million for the nine months ended September 30, 2019 and 2020, respectively. The value of the noncontrolling interest was $9.6 million as of December 31, 2019 and September 30, 2020.

Cash, Cash Equivalents, and Res

Cash, Cash Equivalents, and Restricted Cash	9 Months Ended
	Sep. 30, 2020
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents, and Restricted Cash	Note 4—Cash, Cash Equivalents and Restricted Cash Cash, cash equivalents and restricted cash as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Current assets: ​ ​ Cash and cash equivalents ​ $ 49,207 ​ $ 91,590 Restricted cash - standby letters of credit ​ 15 ​ 15 Total cash, cash equivalents and current portion of restricted cash ​ $ 49,222 ​ $ 91,605 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ 4,000 Total long-term portion of restricted cash ​ $ 4,000 ​ $ 4,000 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 53,222 ​ $ 95,605 ​ 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 balances may be in excess of the Federal Deposit Insurance Corporation (“FDIC”) and Canadian Deposit Insurance Corporation (“CDIC”) limits. 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 $47.9 million and $90.3 million as of December 31, 2019 and September 30, 2020, 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

Short-term Investments	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Short-term Investments	Note 5—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 on available-for-sale 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 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, and evaluates the current expected credit loss. This evaluation is based on a number of factors, including historical experience, market data, issuer-specific factors, economic conditions, and any changes to the credit rating of the security. As of September 30, 2020, the Company has not recorded a credit loss related to available-for-sale debt securities and believes the carrying values for its available-for-sale debt securities are properly recorded. Short-term investments as of December 31, 2019 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Losses Fair Value Municipal bonds and notes ​ $ 2,986 ​ $ — ​ $ 2,986 Zero coupon bonds ​ 33,919 ​ — ​ 33,919 Corporate bonds ​ 19,509 ​ (3) ​ 19,506 Certificates of deposit ​ 518 ​ — ​ 518 Total short-term investments ​ $ 56,932 ​ $ (3) ​ $ 56,929 ​ Short-term investments as of September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Fair Value Certificates of deposit ​ $ 530 ​ $ — ​ $ 530 Total short-term investments ​ $ 530 ​ $ — ​ $ 530 ​

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	9 Months Ended
	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	Note 6 - 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 S.E. and THUSA (as defined in Note 12), for a total of 5.0 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 The Company has entered into fueling agreements with fleet operators under the Zero Now Derivatives and embedded derivatives as of December 31, 2019 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Long-term portion of derivative assets, related party ​ $ 3,270 ​ $ — ​ $ 3,270 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 232 ​ ​ — ​ ​ 232 Notes receivable and other long-term assets, net ​ ​ 491 ​ ​ — ​ ​ 491 Total derivative assets ​ $ 3,993 ​ $ — ​ $ 3,993 Liabilities: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative liabilities, related party ​ $ 164 ​ $ — ​ $ 164 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ ​ 42 ​ ​ — ​ ​ 42 Other long-term liabilities ​ ​ 39 ​ ​ — ​ ​ 39 Total derivative liabilities ​ $ 245 ​ $ — ​ $ 245 ​ Derivatives and embedded derivatives as of September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative assets, related party ​ $ 3,269 ​ $ — ​ $ 3,269 Long-term portion of derivative assets, related party ​ ​ 6,570 ​ ​ — ​ ​ 6,570 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 1 ​ ​ — ​ ​ 1 Notes receivable and other long-term assets, net ​ ​ 125 ​ ​ — ​ ​ 125 Total derivative assets ​ $ 9,965 ​ $ — ​ $ 9,965 Liabilities: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ $ 941 ​ $ — ​ $ 941 Other long-term liabilities ​ ​ 1,261 ​ ​ — ​ ​ 1,261 Total derivative liabilities ​ $ 2,202 ​ $ — ​ $ 2,202 ​ As of December 31, 2019 and September 30, 2020, the Company had a total volume on open commodity swap contracts of 21.9 million and 18.1 million diesel gallons, respectively, at a weighted-average price of approximately $3.18 per gallon. The following table reflects the weighted-average price of open commodity swap contracts as of December 31, 2019 and September 30, 2020, by year with associated volumes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 ​ ​ Volumes ​ Weighted-Average Price per ​ Volumes ​ Weighted-Average Price per Year (Diesel Gallons) Diesel Gallon (Diesel Gallons) Diesel Gallon 2020 5,000,000 ​ $ 3.18 1,250,000 ​ $ 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

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 7—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 certificates of deposit 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 and embedded derivatives in its fueling agreements under the Zero Now The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2019 and September 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.76 - $1.88 ​ $ 1.81 ​ $1.26 - $1.44 ​ $ 1.38 Historical Differential to PADD 3 Diesel ​ $0.79 - $1.16 ​ $ 0.91 ​ $0.81 - $1.58 ​ $ 0.98 Historical Differential to PADD 5 Diesel ​ $1.32 - $2.30 ​ $ 1.78 ​ $1.42 - $2.58 ​ $ 1.98 ​ The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.76 - $1.88 ​ $ 1.81 ​ $1.26 - $1.44 ​ $ 1.38 Historical Differential to PADD 3 Diesel ​ $0.79 - $1.16 ​ $ 0.91 ​ $0.81 - $1.58 ​ $ 0.98 Historical Differential to PADD 5 Diesel ​ $1.32 - $2.30 ​ $ 1.78 ​ $1.42 - $2.58 ​ $ 1.98 ​ The Company’s liability-classified warrants (or "derivative warrants"), which were issued by NG Advantage, are classified within Level 3 because the Company used the Black-Scholes option pricing model to estimate the fair value based on inputs that are not observable in any market. The warrants expired, unexercised, on July 2, 2020. 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, 2019 or September 30, 2020. 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, 2019 and September 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 2,986 ​ $ — ​ $ 2,986 ​ $ — Zero coupon bonds ​ 33,919 ​ — ​ 33,919 ​ — Corporate bonds ​ 19,506 ​ — ​ 19,506 ​ — Certificates of deposit (1) ​ 518 ​ — ​ 518 ​ — Commodity swap contracts (2) ​ ​ 3,270 ​ — ​ — ​ 3,270 Embedded derivatives (3) ​ ​ 723 ​ ​ — ​ ​ — ​ ​ 723 Liabilities: ​ ​ ​ ​ ​ Commodity swap contracts (2) ​ $ 164 ​ $ — ​ $ — ​ $ 164 Embedded derivatives (3) ​ ​ 81 ​ ​ — ​ ​ — ​ ​ 81 Warrants (4) ​ ​ 40 ​ ​ — ​ ​ — ​ ​ 40 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 Level 1 Level 2 Level 3 Assets: ​ ​ ​ Certificates of deposit (1) ​ $ 530 ​ $ — ​ $ 530 ​ $ — Commodity swap contracts (2) ​ 9,839 ​ — ​ — ​ 9,839 Embedded derivatives (3) ​ ​ 126 ​ ​ — ​ ​ — ​ ​ 126 Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ Embedded derivatives (3) ​ $ 2,202 ​ $ — ​ $ — ​ $ 2,202 ​ (1) Included in "Short-term investments" in the accompanying condensed consolidated balance sheets. See Note 5 for more information. (2) Included in “Derivative liabilities, related party” and "Long-term portion of derivative assets, related party’ as of December 31, 2019, and "Derivative assets, related party" and "Long-term portion of derivative assets, related party" as of September 30, 2020, in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (3) Included in "Prepaid expenses and other current assets", “Notes receivable and other long-term assets, net", “Accrued liabilities” and “Other long-term liabilities” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (4) Included in "Accrued liabilities" in the accompanying condensed consolidated balance sheet as of December 31, 2019. The warrants expired on July 2, 2020. ​ The following tables provide 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), as well as the change in unrealized gains or losses for the periods included in earnings (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ Assets: ​ Liabilities: ​ Liabilities: ​ ​ ​ ​ Commodity ​ Embedded ​ Commodity ​ Embedded ​ Liabilities: ​ Swap Contracts Derivatives ​ Swap Contracts ​ Derivatives Warrants Balance as of June 30, 2019 ​ $ 5,696 ​ $ 450 ​ $ — ​ $ — ​ $ (2,676) Settlements, net ​ ​ 1 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ 976 ​ 152 ​ — ​ — ​ 10 Balance as of September 30, 2019 ​ $ 6,673 ​ $ 602 ​ $ — ​ $ — ​ $ (2,666) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of June 30, 2020 ​ $ 9,743 ​ $ 94 ​ $ — ​ $ (1,924) ​ $ — Settlements, net ​ ​ (534) ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ 630 ​ ​ 32 ​ ​ — ​ ​ (278) ​ ​ — Balance as of September 30, 2020 ​ $ 9,839 ​ $ 126 ​ $ — ​ $ (2,202) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the three months ended September 30, 2019 included in earnings ​ $ 977 ​ $ 152 ​ $ — ​ $ — ​ $ 10 Change in unrealized gain (loss) for the three months ended September 30, 2020 included in earnings ​ $ 96 ​ $ 32 ​ $ — ​ $ (278) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ Assets: ​ Liabilities: ​ Liabilities: ​ ​ ​ ​ Commodity ​ Embedded ​ Commodity ​ Embedded ​ Liabilities: ​ Swap Contracts Derivatives ​ Swap Contracts ​ Derivatives Warrants Balance as of December 31, 2018 ​ $ 10,332 ​ $ — ​ $ — ​ $ — ​ $ (1,079) Settlements, net ​ ​ 210 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ (3,869) ​ 602 ​ — ​ — ​ (1,587) Balance as of September 30, 2019 ​ $ 6,673 ​ $ 602 ​ $ — ​ $ — ​ $ (2,666) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of December 31, 2019 ​ $ 3,270 ​ $ 723 ​ $ (164) ​ $ (81) ​ $ (40) Settlements, net ​ ​ (1,011) ​ ​ — ​ ​ 56 ​ ​ — ​ ​ — Total gain (loss) ​ 7,580 ​ ​ (597) ​ ​ 108 ​ ​ (2,121) ​ ​ 40 Balance as of September 30, 2020 ​ $ 9,839 ​ $ 126 ​ $ — ​ $ (2,202) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the nine months ended September 30, 2019 included in earnings ​ $ (3,659) ​ $ 602 ​ $ — ​ $ — ​ $ (1,587) Change in unrealized gain (loss) for the nine months ended September 30, 2020 included in earnings ​ $ 6,569 ​ $ (597) ​ $ 164 ​ $ (2,121) ​ $ 40 ​ 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, 2019 and September 30, 2020. The fair values of these debt instruments were estimated using a DCF 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.

Other Receivables

Other Receivables	9 Months Ended
	Sep. 30, 2020
Receivables [Abstract]
Other Receivables	Note 8—Other Receivables Other receivables as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 2020 Loans to customers to finance vehicle purchases ​ $ 653 ​ $ 386 Accrued customer billings ​ 6,124 ​ 6,066 Fuel tax credits ​ 69,585 ​ 14,994 Other ​ 8,536 ​ 1,706 Total other receivables ​ $ 84,898 ​ $ 23,152 ​

Inventory

Inventory	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventory	Note 9—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, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Raw materials and spare parts ​ $ 29,874 ​ $ 28,830 Total inventory ​ $ 29,874 ​ $ 28,830 ​

Land, Property and Equipment

Land, Property and Equipment	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Land, Property and Equipment	Note 10—Land, Property and Equipment Land, property and equipment, net as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ 2019 2020 Land ​ $ 3,476 ​ $ 3,476 LNG liquefaction plants ​ 94,633 ​ 94,633 Station equipment ​ 324,431 ​ 347,636 Trailers ​ 79,477 ​ 79,670 Other equipment ​ 101,655 ​ 86,921 Construction in progress ​ 75,232 ​ 71,597 ​ ​ 678,904 ​ 683,933 Less accumulated depreciation ​ (354,992) ​ (385,845) Total land, property and equipment, net ​ $ 323,912 ​ $ 298,088 ​ Included in "Land, property and equipment, net" are capitalized software costs of $30.4 million and $31.6 million as of December 31, 2019 and September 30, 2020, respectively. Accumulated amortization of the capitalized software costs is $26.3 million and $28.2 million as of December 31, 2019 and September 30, 2020, respectively. The Company recorded amortization expense related to capitalized software costs of $1.0 million and $0.6 million for the three months ended September 30, 2019 and 2020, respectively, and $3.1 million and $1.9 million for the nine months ended September 30, 2019 and 2020, respectively. As of September 30, 2019 and 2020, $2.2 million and $0.9 million, respectively, is 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

Accrued Liabilities	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Accrued Liabilities	Note 11—Accrued Liabilities Accrued liabilities as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ​ 2019 2020 Accrued alternative fuels incentives (1) ​ $ 27,839 ​ $ 14,738 Accrued employee benefits ​ 2,276 ​ 3,647 Accrued interest ​ 220 ​ 310 Accrued gas and equipment purchases ​ 11,383 ​ 9,724 Accrued property and other taxes ​ 3,732 ​ 2,947 Accrued salaries and wages ​ 9,105 ​ 7,711 Embedded derivatives ​ ​ 42 ​ ​ 941 Other (2) ​ 13,100 ​ 10,184 Total accrued liabilities ​ $ 67,697 ​ $ 50,202 (1) Includes the amount of RINs, LCFS Credits and the amount of AFTC payable to third parties. (2) No individual item in “Other” exceeds 5% of total current liabilities .

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	Note 12—Debt Debt obligations as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs 7.5% Notes ​ $ 50,000 $ 17 ​ $ 49,983 NG Advantage debt ​ 33,898 ​ 192 ​ 33,706 SG Facility ​ ​ 4,400 ​ ​ — ​ ​ 4,400 Other debt ​ 796 ​ — ​ 796 Total debt ​ 89,094 ​ 209 ​ 88,885 Less amounts due within one year ​ (56,097) ​ (84) ​ (56,013) Total long-term debt ​ $ 32,997 ​ $ 125 ​ $ 32,872 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs NG Advantage debt ​ $ 30,057 $ 147 ​ $ 29,910 SG Facility ​ ​ 4,700 ​ ​ — ​ ​ 4,700 Other debt ​ 563 ​ — ​ 563 Total debt ​ 35,320 ​ 147 ​ 35,173 Less amounts due within one year ​ (6,193) ​ ​ (67) ​ (6,126) Total long-term debt ​ $ 29,127 ​ $ 80 ​ $ 29,047 ​ 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 $150.0 million. The 7.5% Notes bore interest at the rate of 7.5% per annum and were 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 had 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 could force conversion of each 7.5% Note into shares of its common stock if such shares traded 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 7.5% Notes included customary events of default which, if any of them occurred, would permit or require the principal of, and accrued interest on, the 7.5% Notes to become, or to be declared, due and payable. Prior to January 1, 2018, (i) the Company purchased $25.0 million of the 7.5% Notes from Mr. Pickens, (ii) Mr. Pickens transferred the remaining balance of his 7.5% Notes to third parties, and (iii) GEIH transferred $16.8 million in principal amount of its 7.5% Notes to third parties. As of December 31, 2019, (i) GEIH held 7.5% Notes in an aggregate principal amount of $32.9 million, and (ii) other third parties held 7.5% Notes in an aggregate principal amount of $17.1 million, all of which were due June 14, 2020. In May 2020, the Company repaid the remaining $50.0 million of 7.5% Notes and related accrued and unpaid interest thereon. No events of default under the 7.5% Notes had occurred as of the date such 7.5% Notes were paid in full. SG Credit Agreement 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 $100.0 million of loans (“SG Loans”) in support of its Zero Now Zero Now Zero Now 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. As of September 30, 2020, the Company had $4.7 million outstanding on the SG Facility and no events of defaults had occurred. TOTAL Credit Support Agreement On January 2, 2019, the Company entered into a credit support agreement (“CSA”) with Total Holdings USA Inc. (“THUSA”), a wholly owned subsidiary of TOTAL S.E. 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 $100.0 million in SG 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 SG Loan amount for the preceding calendar quarter. Following any payment by THUSA to SG under the Guaranty, the Company would be obligated to immediately pay to THUSA the full amount of such payment plus interest on such amount at a rate equal to LIBOR plus 1.0%. In addition, the Company would be obligated to pay and reimburse THUSA for all reasonable out-of-pocket expenses it incurs in the performance of its services under the CSA, including all reasonable out-of-pocket attorneys’ fees and expenses incurred in connection with the payment to SG under the Guaranty or any enforcement or attempt to enforce any of the Company‘s obligations under the CSA. The CSA includes customary representations and warranties and affirmative and negative covenants by the Company. In addition, upon the occurrence of a “Trigger Event” and during its continuation, THUSA may, among other things: elect not to guarantee additional SG Loans; declare all or any portion of the outstanding amounts the Company owes THUSA under the CSA to be due and payable; and exercise all other rights it may have under applicable law. Each of the following events constitutes a Trigger Event: the Company defaults with respect to any payment obligation under the CSA; any representation or warranty made by the Company in the CSA was false, incorrect, incomplete or misleading in any material respect when made; the Company fails to observe or perform any material covenant, obligation, condition or agreement in the CSA; or the Company defaults in the observance or performance of any agreement, term or condition contained in any other agreement with THUSA or an affiliate of THUSA. 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 Zero Now Until the occurrence of a Trigger Event or Fundamental Trigger Event (as described below) under the CSA, the Company has the freedom to operate in the normal course and there are no restrictions on the flow of funds in and out of the lockbox account established pursuant to the lockbox agreement. Upon the occurrence of a Trigger Event under the CSA, all funds in the lockbox account will be: first, used to make scheduled debt repayments under the Credit Agreement; and second, released to the Company. Further, upon the occurrence of a “Fundamental Trigger Event” under the CSA and during its continuation, in addition to exercising any of the remedies available to THUSA upon the occurrence of a Trigger Event as described above: all participants in the Zero Now 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 SG 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 $6.3 million and $6.2 million, 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 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 $4.7 million. The proceeds were primarily used to fund the purchases of CNG trailers and equipment. Interest and principal are 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 $2.1 million 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 at an annual rate of 4.86%. 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 $6.3 million 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 at an annual rate of 9.28%. On December 20, 2018 (the “Closing Date”), NG Advantage entered into a purchase agreement to sell a compression station for a purchase price of $7.0 million to an entity whose member owners were 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 $0.1 million at an annual rate of 12.0%. Of the purchase price, NG Advantage received $4.7 million in cash, net of fees, the first month’s lease payment, and the repayment of a $2.0 million 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 $3.4 million 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 at an annual rate of 9.18%. In October 2019, NG Advantage entered into a sale-leaseback agreement, pursuant to which it sold compression equipment for a purchase price of $7.5 million and simultaneously leased it back for a term of five years with interest and principal payable in equal monthly installments at an annual rate of 10.47%. Of the purchase price, NG Advantage received $5.3 million in cash and $2.2 million was held as a security deposit. Other Debt As of September 30, 2020, the Company has other debt due through May 2023 bearing interest at 4.75%.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Note 13—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 following table sets forth the computations of basic and diluted earnings (loss) per share for the three and nine months ended September 30, 2019 and 2020 (in thousands except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ September 30, ​ September 30, ​ ​ 2019 2020 2019 2020 Net loss attributable to Clean Energy Fuels Corp. ​ $ (4,334) ​ $ (2,271) ​ $ (20,663) ​ $ (7,303) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ 204,712,888 ​ 198,785,394 ​ 204,522,984 ​ 201,472,851 Dilutive effect of potential common shares from restricted stock units and stock options ​ — ​ — ​ — ​ — Weighted-average common shares outstanding - diluted ​ 204,712,888 ​ 198,785,394 ​ 204,522,984 ​ 201,472,851 Basic and diluted loss per share ​ $ (0.02) ​ $ (0.01) ​ $ (0.10) ​ $ (0.04) ​ 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 ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Stock options 10,051,402 ​ 9,434,211 ​ 10,051,402 ​ 9,434,211 Convertible notes 3,164,557 ​ — ​ 3,164,557 ​ 1,486,418 Restricted stock units 1,257,873 ​ 988,980 ​ 1,257,873 ​ 988,980 Total ​ 14,473,832 ​ 10,423,191 ​ 14,473,832 ​ 11,909,609 ​

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Note 14—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 three and nine months ended September 30, 2019 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Stock-based compensation expense, net of $0 tax in 2019 and 2020 ​ $ 892 ​ $ 708 ​ $ 3,056 ​ $ 2,522 ​ As of September 30, 2020, there was $3.3 million 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 1.5 years. In May 2020, the Company adopted its Amended and Restated 2016 Performance Incentive Plan (“Amended 2016 Plan”), which increased the aggregate number of shares of the Company’s common stock to be delivered pursuant to all awards granted under the 2016 Performance Incentive Plan by an additional 17,500,000 shares, and became effective on May 18, 2020, the date of approval of the Amended 2016 Plan by the Company’s stockholders.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Stockholders' Equity	Note 15—Stockholders’ Equity Share Repurchase Program On March 12, 2020, the Company’s Board of Directors approved a share repurchase program of up to $30.0 million (exclusive of fees and commissions) of the Company’s outstanding common stock (the “Repurchase Program”). The Repurchase Program does not have an expiration date, and it may be suspended or discontinued at any time. As of September 30, 2020, the Company had utilized $13.5 million under the Repurchase Program to repurchase 7,347,691 shares of its common stock for a total cost of $13.7 million. The Repurchase Program does not obligate the Company to acquire any specific number of shares. Repurchases under the Repurchase Program may be effected from time to time through open market purchases, privately negotiated transactions, structured or derivative transactions, including accelerated share repurchase transactions, or other methods of acquiring shares, in each case subject to market conditions, applicable securities laws and other relevant factors. Repurchases may also be made under Rule 10b5-1 plans.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Note 16—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 $0.1 million for each of the three months ended September 30, 2019 and 2020, and $0.2 million for each of the nine months ended September 30, 2019 and 2020. Tax expense for all periods consists of taxes due on the Company’s U.S. and foreign operations. The effective tax rates for the three and nine months ended September 30, 2019 and 2020 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 nine months ended September 30, 2020 by $1.7 million. This increase is the portion of AFTC revenue recognized in the period attributed to the federal fuel tax the Company collected from its customers during the nine months ended September 30, 2020. The net interest incurred was immaterial for both the nine months ended September 30, 2019 and 2020.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 17—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 effect 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 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

Leases	9 Months Ended
	Sep. 30, 2020
Leases
Leases	Note 18—Leases Lessor Accounting The Company leases fueling station equipment to customers pursuant to agreements 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 accompanying 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 September 30, 2019 and 2020, the Company recognized $0.0 million and $0.1 million, respectively, in “Interest income” on its lease receivables. During the nine months ended September 30, 2019 and 2020, the Company recognized $0.1 million and $0.4 million, respectively, in “Interest income” on its lease receivables. The following schedule represents the Company’s maturities of lease receivables as of September 30, 2020 (in thousands): ​ ​ ​ ​ ​ Fiscal year: ​ Remainder of 2020 ​ $ 350 2021 ​ 1,402 2022 ​ 1,182 2023 ​ 962 2024 ​ 962 Thereafter ​ 4,320 Total minimum lease payments ​ 9,178 Less amount representing interest ​ (2,472) Present value of lease receivables ​ $ 6,706 ​ ​

Alternative Fuels Excise Tax Cr

Alternative Fuels Excise Tax Credit	9 Months Ended
	Sep. 30, 2020
Alternative Fuel Excise Tax Credit
Alternative Fuels Excise Tax Credit	Note 19—Alternative Fuel Excise Tax Credit Under separate pieces of U.S. federal legislation, the Company has been eligible to receive the AFTC for its natural gas vehicle fuel sales made between October 1, 2006 and September 30, 2020. On December 20, 2019, the AFTC, which had previously expired, was retroactively reinstated and extended beginning January 1, 2018 through December 31, 2020. The AFTC 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 2019 and 2020. Based on the service relationship with its customers, either the Company or its customers claim the credit. The Company records its AFTC, if any, as revenue in its condensed 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 December 20, 2019, all AFTC revenue for vehicle fuel the Company sold in the 2018 and 2019 calendar years, totaling $47.1 million, was recognized during the three months ended December 31, 2019. During the three and nine months ended September 30, 2020, the Company recognized AFTC revenue of $5.0 million and $14.8 million, respectively, for vehicle fuel the Company sold during each of these periods. AFTC is available through December 31, 2020 and may not be reinstated for vehicle fuel sales made after that date.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transaction	Note 20—Related Party Transactions TOTAL S.E. During the three and nine months ended September 30, 2019, the Company recognized revenue of $0.0 million and $1.7 million, respectively, related to RINs sold to TOTAL S.E. and its affiliates (“TOTAL”) in the ordinary course of business. During the three and nine months ended September 30, 2020, the Company recognized revenue of $2.6 million and $5.3 million, respectively, related to RINs and LNG sold to TOTAL in the ordinary course of business and settlements on commodity swap contracts (Note 6). As of December 31, 2019 and September 30, 2020, the Company had receivables from TOTAL of zero and $1.0 million, respectively. During the three and nine months ended September 30, 2019, the Company paid TOTAL $0.4 million and $0.9 million for expenses incurred in the ordinary course of business and settlements on commodity swap contracts (Note 6). During the three and nine months ended September 30, 2020, the Company paid TOTAL $0.1 million and $0.5 million, respectively, for expenses incurred in the ordinary course of business, settlements on commodity swap contracts (Note 6), and the guaranty fee under the CSA (Note 12). As of December 31, 2019 and September 30, 2020, the amount due to TOTAL was immaterial. SAFE&CEC S.r.l. During the three and nine months ended September 30, 2019, the Company received $0.0 million and $0.2 million, respectively, from SAFE&CEC S.r.l. in the ordinary course of business. During the three and nine months ended September 30, 2020, the Company received $0.2 million and $1.2 million, respectively, from SAFE&CEC S.r.l. in the ordinary course of business. As of December 31, 2019 and September 30, 2020, the Company had receivables from SAFE&CEC S.r.l. of $0.9 million and $0.1 million, respectively. During the three and nine months ended September 30, 2019, the Company paid SAFE&CEC S.r.l. $0.6 million and $2.1 million, respectively, for parts and equipment in the ordinary course of business. During the three and nine months ended September 30, 2020, the Company paid SAFE&CEC S.r.l. $1.5 million and $4.3 million, respectively, for parts and equipment in the ordinary course of business. As of December 31, 2019 and September 30, 2020, the Company had payables to SAFE&CEC S.r.l. of $0.8 million and $0.5 million, respectively.

General (Policies)

General (Policies)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to state fairly the Company’s consolidated financial position as of September 30, 2020, results of operations, comprehensive loss, and stockholders’ equity for the three and nine months ended September 30, 2019 and 2020, and cash flows for the nine months ended September 30, 2019 and 2020. All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and nine month periods ended September 30, 2019 and 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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 (“U.S. 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, 2019 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 10, 2020.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. 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.
Recently Adopted Accounting Changes and Recently Issued Accounting Standards	Recently Adopted Accounting Pronouncements ​ In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ​ Recently Issued Accounting Pronouncements Pending Adoption ​ In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes
Revenue Recognition	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.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Volume-related (1) ​ $ 67,869 ​ $ 57,127 ​ $ 208,667 ​ $ 182,417 Station construction sales ​ 6,431 ​ 8,743 ​ 15,544 ​ 19,543 AFTC (2) ​ — ​ 5,016 ​ — ​ 14,806 Other ​ 134 ​ — ​ 239 ​ — Total revenue ​ $ 74,434 ​ $ 70,886 ​ $ 224,450 ​ $ 216,766 (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts associated with the Company’s Zero Now truck financing program. 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 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 and nine months ended September 30, 2019, changes in the fair value of commodity swaps and customer fueling contracts amounted to a gain of $1.1 million and a loss of $3.3 million, respectively. For the three and nine months ended September 30, 2020, changes in the fair value of commodity swaps and customer fueling contracts amounted to a loss of $0.1 million and a gain of $4.0 million, respectively. (2) Represents the federal alternative fuel excise tax credit that we refer to as “AFTC,” which had previously expired but on December 20, 2019 was retroactively extended for vehicle fuel sales made beginning January 1, 2018 through December 31, 2020. See Note 19 for more information.
Summary of contract balances	As of December 31, 2019 and September 30, 2020, the Company’s contract balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Accounts receivable, net ​ $ 61,760 ​ $ 52,904 ​ ​ ​ ​ ​ Contract assets - current ​ $ 455 ​ $ 955 Contract assets - non-current ​ 3,777 ​ 3,854 Contract assets - total ​ $ 4,232 ​ $ 4,809 ​ ​ ​ ​ ​ Contract liabilities - current ​ $ 5,329 ​ $ 938 Contract liabilities - non-current ​ 6,339 ​ — Contract liabilities - total ​ $ 11,668 ​ $ 938

Cash, Cash Equivalents, and R_2

Cash, Cash Equivalents, and Restricted Cash (Tables)	9 Months Ended
	Sep. 30, 2020
Cash and Cash Equivalents [Abstract]
Schedule of cash and cash equivalents	Cash, cash equivalents and restricted cash as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Current assets: ​ ​ Cash and cash equivalents ​ $ 49,207 ​ $ 91,590 Restricted cash - standby letters of credit ​ 15 ​ 15 Total cash, cash equivalents and current portion of restricted cash ​ $ 49,222 ​ $ 91,605 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ 4,000 Total long-term portion of restricted cash ​ $ 4,000 ​ $ 4,000 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 53,222 ​ $ 95,605
Schedule of components of restricted cash	Cash, cash equivalents and restricted cash as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Current assets: ​ ​ Cash and cash equivalents ​ $ 49,207 ​ $ 91,590 Restricted cash - standby letters of credit ​ 15 ​ 15 Total cash, cash equivalents and current portion of restricted cash ​ $ 49,222 ​ $ 91,605 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ 4,000 Total long-term portion of restricted cash ​ $ 4,000 ​ $ 4,000 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 53,222 ​ $ 95,605

Short-term Investments (Tables)

Short-term Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Summary of short-term investments	Short-term investments as of December 31, 2019 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Losses Fair Value Municipal bonds and notes ​ $ 2,986 ​ $ — ​ $ 2,986 Zero coupon bonds ​ 33,919 ​ — ​ 33,919 Corporate bonds ​ 19,509 ​ (3) ​ 19,506 Certificates of deposit ​ 518 ​ — ​ 518 Total short-term investments ​ $ 56,932 ​ $ (3) ​ $ 56,929 ​ Short-term investments as of September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gains Fair Value Certificates of deposit ​ $ 530 ​ $ — ​ $ 530 Total short-term investments ​ $ 530 ​ $ — ​ $ 530

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	9 Months Ended
	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of commodity derivative activity	Derivatives and embedded derivatives as of December 31, 2019 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Long-term portion of derivative assets, related party ​ $ 3,270 ​ $ — ​ $ 3,270 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 232 ​ ​ — ​ ​ 232 Notes receivable and other long-term assets, net ​ ​ 491 ​ ​ — ​ ​ 491 Total derivative assets ​ $ 3,993 ​ $ — ​ $ 3,993 Liabilities: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative liabilities, related party ​ $ 164 ​ $ — ​ $ 164 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ ​ 42 ​ ​ — ​ ​ 42 Other long-term liabilities ​ ​ 39 ​ ​ — ​ ​ 39 Total derivative liabilities ​ $ 245 ​ $ — ​ $ 245 ​ Derivatives and embedded derivatives as of September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative assets, related party ​ $ 3,269 ​ $ — ​ $ 3,269 Long-term portion of derivative assets, related party ​ ​ 6,570 ​ ​ — ​ ​ 6,570 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 1 ​ ​ — ​ ​ 1 Notes receivable and other long-term assets, net ​ ​ 125 ​ ​ — ​ ​ 125 Total derivative assets ​ $ 9,965 ​ $ — ​ $ 9,965 Liabilities: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ $ 941 ​ $ — ​ $ 941 Other long-term liabilities ​ ​ 1,261 ​ ​ — ​ ​ 1,261 Total derivative liabilities ​ $ 2,202 ​ $ — ​ $ 2,202
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, 2019 and September 30, 2020, by year with associated volumes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 ​ ​ Volumes ​ Weighted-Average Price per ​ Volumes ​ Weighted-Average Price per Year (Diesel Gallons) Diesel Gallon (Diesel Gallons) Diesel Gallon 2020 5,000,000 ​ $ 3.18 1,250,000 ​ $ 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

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of estimated fair value of outstanding commodity swap contracts and embedded derivatives	The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2019 and September 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.76 - $1.88 ​ $ 1.81 ​ $1.26 - $1.44 ​ $ 1.38 Historical Differential to PADD 3 Diesel ​ $0.79 - $1.16 ​ $ 0.91 ​ $0.81 - $1.58 ​ $ 0.98 Historical Differential to PADD 5 Diesel ​ $1.32 - $2.30 ​ $ 1.78 ​ $1.42 - $2.58 ​ $ 1.98 ​ The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ September 30, 2020 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.76 - $1.88 ​ $ 1.81 ​ $1.26 - $1.44 ​ $ 1.38 Historical Differential to PADD 3 Diesel ​ $0.79 - $1.16 ​ $ 0.91 ​ $0.81 - $1.58 ​ $ 0.98 Historical Differential to PADD 5 Diesel ​ $1.32 - $2.30 ​ $ 1.78 ​ $1.42 - $2.58 ​ $ 1.98
Schedule of information by level for assets and liabilities that are measured at fair value on a recurring basis	The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2019 and September 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 2,986 ​ $ — ​ $ 2,986 ​ $ — Zero coupon bonds ​ 33,919 ​ — ​ 33,919 ​ — Corporate bonds ​ 19,506 ​ — ​ 19,506 ​ — Certificates of deposit (1) ​ 518 ​ — ​ 518 ​ — Commodity swap contracts (2) ​ ​ 3,270 ​ — ​ — ​ 3,270 Embedded derivatives (3) ​ ​ 723 ​ ​ — ​ ​ — ​ ​ 723 Liabilities: ​ ​ ​ ​ ​ Commodity swap contracts (2) ​ $ 164 ​ $ — ​ $ — ​ $ 164 Embedded derivatives (3) ​ ​ 81 ​ ​ — ​ ​ — ​ ​ 81 Warrants (4) ​ ​ 40 ​ ​ — ​ ​ — ​ ​ 40 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 Level 1 Level 2 Level 3 Assets: ​ ​ ​ Certificates of deposit (1) ​ $ 530 ​ $ — ​ $ 530 ​ $ — Commodity swap contracts (2) ​ 9,839 ​ — ​ — ​ 9,839 Embedded derivatives (3) ​ ​ 126 ​ ​ — ​ ​ — ​ ​ 126 Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ Embedded derivatives (3) ​ $ 2,202 ​ $ — ​ $ — ​ $ 2,202 ​ (1) Included in "Short-term investments" in the accompanying condensed consolidated balance sheets. See Note 5 for more information. (2) Included in “Derivative liabilities, related party” and "Long-term portion of derivative assets, related party’ as of December 31, 2019, and "Derivative assets, related party" and "Long-term portion of derivative assets, related party" as of September 30, 2020, in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (3) Included in "Prepaid expenses and other current assets", “Notes receivable and other long-term assets, net", “Accrued liabilities” and “Other long-term liabilities” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (4) Included in "Accrued liabilities" in the accompanying condensed consolidated balance sheet as of December 31, 2019. The warrants expired on July 2, 2020.
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)	The following tables provide 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), as well as the change in unrealized gains or losses for the periods included in earnings (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ Assets: ​ Liabilities: ​ Liabilities: ​ ​ ​ ​ Commodity ​ Embedded ​ Commodity ​ Embedded ​ Liabilities: ​ Swap Contracts Derivatives ​ Swap Contracts ​ Derivatives Warrants Balance as of June 30, 2019 ​ $ 5,696 ​ $ 450 ​ $ — ​ $ — ​ $ (2,676) Settlements, net ​ ​ 1 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ 976 ​ 152 ​ — ​ — ​ 10 Balance as of September 30, 2019 ​ $ 6,673 ​ $ 602 ​ $ — ​ $ — ​ $ (2,666) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of June 30, 2020 ​ $ 9,743 ​ $ 94 ​ $ — ​ $ (1,924) ​ $ — Settlements, net ​ ​ (534) ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ 630 ​ ​ 32 ​ ​ — ​ ​ (278) ​ ​ — Balance as of September 30, 2020 ​ $ 9,839 ​ $ 126 ​ $ — ​ $ (2,202) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the three months ended September 30, 2019 included in earnings ​ $ 977 ​ $ 152 ​ $ — ​ $ — ​ $ 10 Change in unrealized gain (loss) for the three months ended September 30, 2020 included in earnings ​ $ 96 ​ $ 32 ​ $ — ​ $ (278) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ Assets: ​ Liabilities: ​ Liabilities: ​ ​ ​ ​ Commodity ​ Embedded ​ Commodity ​ Embedded ​ Liabilities: ​ Swap Contracts Derivatives ​ Swap Contracts ​ Derivatives Warrants Balance as of December 31, 2018 ​ $ 10,332 ​ $ — ​ $ — ​ $ — ​ $ (1,079) Settlements, net ​ ​ 210 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Total gain (loss) ​ (3,869) ​ 602 ​ — ​ — ​ (1,587) Balance as of September 30, 2019 ​ $ 6,673 ​ $ 602 ​ $ — ​ $ — ​ $ (2,666) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of December 31, 2019 ​ $ 3,270 ​ $ 723 ​ $ (164) ​ $ (81) ​ $ (40) Settlements, net ​ ​ (1,011) ​ ​ — ​ ​ 56 ​ ​ — ​ ​ — Total gain (loss) ​ 7,580 ​ ​ (597) ​ ​ 108 ​ ​ (2,121) ​ ​ 40 Balance as of September 30, 2020 ​ $ 9,839 ​ $ 126 ​ $ — ​ $ (2,202) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the nine months ended September 30, 2019 included in earnings ​ $ (3,659) ​ $ 602 ​ $ — ​ $ — ​ $ (1,587) Change in unrealized gain (loss) for the nine months ended September 30, 2020 included in earnings ​ $ 6,569 ​ $ (597) ​ $ 164 ​ $ (2,121) ​ $ 40

Other Receivables (Tables)

Other Receivables (Tables)	9 Months Ended
	Sep. 30, 2020
Receivables [Abstract]
Schedule of other receivables	Other receivables as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 2020 Loans to customers to finance vehicle purchases ​ $ 653 ​ $ 386 Accrued customer billings ​ 6,124 ​ 6,066 Fuel tax credits ​ 69,585 ​ 14,994 Other ​ 8,536 ​ 1,706 Total other receivables ​ $ 84,898 ​ $ 23,152

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Schedule of inventories	Inventory as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ ​ 2019 ​ 2020 Raw materials and spare parts ​ $ 29,874 ​ $ 28,830 Total inventory ​ $ 29,874 ​ $ 28,830

Land, Property and Equipment (T

Land, Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Summary of land, property and equipment	Land, property and equipment, net as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, September 30, ​ 2019 2020 Land ​ $ 3,476 ​ $ 3,476 LNG liquefaction plants ​ 94,633 ​ 94,633 Station equipment ​ 324,431 ​ 347,636 Trailers ​ 79,477 ​ 79,670 Other equipment ​ 101,655 ​ 86,921 Construction in progress ​ 75,232 ​ 71,597 ​ ​ 678,904 ​ 683,933 Less accumulated depreciation ​ (354,992) ​ (385,845) Total land, property and equipment, net ​ $ 323,912 ​ $ 298,088

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Schedule of accrued liabilities	Accrued liabilities as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ September 30, ​ 2019 2020 Accrued alternative fuels incentives (1) ​ $ 27,839 ​ $ 14,738 Accrued employee benefits ​ 2,276 ​ 3,647 Accrued interest ​ 220 ​ 310 Accrued gas and equipment purchases ​ 11,383 ​ 9,724 Accrued property and other taxes ​ 3,732 ​ 2,947 Accrued salaries and wages ​ 9,105 ​ 7,711 Embedded derivatives ​ ​ 42 ​ ​ 941 Other (2) ​ 13,100 ​ 10,184 Total accrued liabilities ​ $ 67,697 ​ $ 50,202 (1) Includes the amount of RINs, LCFS Credits and the amount of AFTC payable to third parties. (2) No individual item in “Other” exceeds 5% of total current liabilities .

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of long-term debt	Debt obligations as of December 31, 2019 and September 30, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs 7.5% Notes ​ $ 50,000 $ 17 ​ $ 49,983 NG Advantage debt ​ 33,898 ​ 192 ​ 33,706 SG Facility ​ ​ 4,400 ​ ​ — ​ ​ 4,400 Other debt ​ 796 ​ — ​ 796 Total debt ​ 89,094 ​ 209 ​ 88,885 Less amounts due within one year ​ (56,097) ​ (84) ​ (56,013) Total long-term debt ​ $ 32,997 ​ $ 125 ​ $ 32,872 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs NG Advantage debt ​ $ 30,057 $ 147 ​ $ 29,910 SG Facility ​ ​ 4,700 ​ ​ — ​ ​ 4,700 Other debt ​ 563 ​ — ​ 563 Total debt ​ 35,320 ​ 147 ​ 35,173 Less amounts due within one year ​ (6,193) ​ ​ (67) ​ (6,126) Total long-term debt ​ $ 29,127 ​ $ 80 ​ $ 29,047

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of information required to compute basic and diluted net loss per share	The following table sets forth the computations of basic and diluted earnings (loss) per share for the three and nine months ended September 30, 2019 and 2020 (in thousands except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ September 30, ​ September 30, ​ ​ 2019 2020 2019 2020 Net loss attributable to Clean Energy Fuels Corp. ​ $ (4,334) ​ $ (2,271) ​ $ (20,663) ​ $ (7,303) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ 204,712,888 ​ 198,785,394 ​ 204,522,984 ​ 201,472,851 Dilutive effect of potential common shares from restricted stock units and stock options ​ — ​ — ​ — ​ — Weighted-average common shares outstanding - diluted ​ 204,712,888 ​ 198,785,394 ​ 204,522,984 ​ 201,472,851 Basic and diluted loss per share ​ $ (0.02) ​ $ (0.01) ​ $ (0.10) ​ $ (0.04)
Schedule of potentially dilutive securities that have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive	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 ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Stock options 10,051,402 ​ 9,434,211 ​ 10,051,402 ​ 9,434,211 Convertible notes 3,164,557 ​ — ​ 3,164,557 ​ 1,486,418 Restricted stock units 1,257,873 ​ 988,980 ​ 1,257,873 ​ 988,980 Total ​ 14,473,832 ​ 10,423,191 ​ 14,473,832 ​ 11,909,609

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
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	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 three and nine months ended September 30, 2019 and 2020 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2019 2020 2019 2020 Stock-based compensation expense, net of $0 tax in 2019 and 2020 ​ $ 892 ​ $ 708 ​ $ 3,056 ​ $ 2,522

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2020
Leases
Schedule of maturities of lease receivables	The following schedule represents the Company’s maturities of lease receivables as of September 30, 2020 (in thousands): ​ ​ ​ ​ ​ Fiscal year: ​ Remainder of 2020 ​ $ 350 2021 ​ 1,402 2022 ​ 1,182 2023 ​ 962 2024 ​ 962 Thereafter ​ 4,320 Total minimum lease payments ​ 9,178 Less amount representing interest ​ (2,472) Present value of lease receivables ​ $ 6,706

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contracts with Customers
Revenue	$ 70,886	$ 74,434	$ 216,766	$ 224,450
Receivables, net	52,904		52,904		$ 61,760
Contract Assets - Current	955		955		455
Contract Assets - Noncurrent	3,854		3,854		3,777
Contract Assets - Total	4,809		4,809		4,232
Contract Liabilities - Current	938		938		5,329
Contract Liabilities - Noncurrent					6,339
Contract Liabilities - Total	938		938		$ 11,668
Volume -Related
Revenue from Contracts with Customers
Revenue	57,127	67,869	182,417	208,667
Gain on derivatives		1,100	4,000
Loss on derivatives	100			3,300
Station construction sales
Revenue from Contracts with Customers
Revenue	8,743	6,431	19,543	15,544
AFTC
Revenue from Contracts with Customers
Revenue	$ 5,016		$ 14,806
Other
Revenue from Contracts with Customers
Revenue		$ 134		$ 239

Revenue - Remaining Performance

Revenue - Remaining Performance Obligations (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Remaining Performance Obligations
Revenue, remaining performance obligation, amount		$ 15.2
Contract with customer, liability, revenue recognized		$ 4.8	$ 4.4
NG Advantage
Remaining Performance Obligations
Payment for termination of contract	$ 7.8
Decrease in contract with customer liability	7
Revenue impact on termination of contract	$ (0.8)
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Remaining Performance Obligations
Revenue, remaining performance obligation, expected timing of satisfaction, period		12 months
Maximum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Remaining Performance Obligations
Revenue, remaining performance obligation, expected timing of satisfaction, period		24 months

Investments in Other Entities_2

Investments in Other Entities and Noncontrolling Interest in a Subsidiary (Details) - USD ($) $ in Thousands	Feb. 29, 2020	Feb. 28, 2018	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 24, 2020	Feb. 06, 2020	Feb. 05, 2020	Dec. 31, 2019	Dec. 29, 2017	Oct. 14, 2014
Acquisition and Divestitures
Income (loss) from equity method investments				$ (11)	$ 377	$ (368)	$ (123)
Payments to acquire additional controlling interest						150
Outstanding balance				35,173		35,173					$ 88,885
Loss from noncontrolling interest				268	1,711	1,374	5,301
BP Products North America | Long-Term Natural Gas Purchase Contracts | NG Advantage
Acquisition and Divestitures
Contingent consideration, liability (up to)		$ 30,000						$ 15,000
Contingent consideration, liability, term		30 days
Payment to terminate a portion of the forgoing arrangement			$ 7,800
Clean Energy Fuels Corp. | NG Advantage | Convertible Debt
Acquisition and Divestitures
Outstanding balance											26,700
SAFE&CEC S.r.l.
Acquisition and Divestitures
Ownership interest												49.00%
Income (loss) from equity method investments				0	400	(400)	0
Investment balance				23,200		23,200					23,700
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				300	$ 1,700	1,400	$ 5,300
Noncontrolling interest, fair value				$ 9,600		$ 9,600					$ 9,600
NG Advantage | Common unit purchase agreement
Acquisition and Divestitures
Ownership interest acquired				93.30%		93.30%			93.20%	64.60%			53.30%
Issuance of equity by subsidiary to parent (in shares)	283,019

Cash, Cash Equivalents and Rest

Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Restricted Cash
Cash and cash equivalents	$ 91,590	$ 49,207
Total cash, cash equivalents and current portion of restricted cash	91,605	49,222
Long-term portion of restricted cash	4,000	4,000
Total cash, cash equivalents and restricted cash	95,605	53,222	$ 37,703	$ 34,624
Amount in excess of FDIC and CDIC limits	90,300	47,900
Standby letters of credit
Restricted Cash
Restricted cash	15	15
Long-term portion of restricted cash	$ 4,000	$ 4,000

Short-Term Investments (Details

Short-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 530	$ 56,932
Gross Unrealized Losses		(3)
Estimated Fair Value	530	56,929
Municipal bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,986
Estimated Fair Value		2,986
Zero coupon bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		33,919
Estimated Fair Value		33,919
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		19,509
Gross Unrealized Losses		(3)
Estimated Fair Value		19,506
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	530	518
Estimated Fair Value	$ 530	$ 518

Derivative Instruments and He_3

Derivative Instruments and Hedging Activities - Narrative (Details) - Not Designated as Hedging Instrument - Commodity swaps gal in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Oct. 31, 2018contractgal	Sep. 30, 2020$ / galgal	Dec. 31, 2019$ / galgal
Derivative [Line Items]
Derivative asset, number of instruments held | contract	2
Volumes (Diesel Gallons) | gal	5	18.1	21.9
Weighted -average price per diesel gallon (in usd per gallon) | $ / gal		3.18	3.18

Derivative Instruments and He_4

Derivative Instruments and Hedging Activities - Summary of Commodity Derivative Activity (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative Assets
Gross Amounts Recognized	$ 9,965	$ 3,993
Net Amount Presented	9,965	3,993
Derivative Liability
Gross Amounts Recognized	2,202	245
Net Amount Presented	2,202	245
Current portion of derivative liabilities, related party | Commodity swaps
Derivative Assets
Gross Amounts Recognized	3,269
Net Amount Presented	3,269
Derivative Liability
Gross Amounts Recognized		164
Net Amount Presented		164
Long-term portion of derivative assets, related party | Commodity swaps
Derivative Assets
Gross Amounts Recognized	6,570	3,270
Net Amount Presented	6,570	3,270
Prepaid expenses and other current assets | Fueling agreements
Derivative Assets
Gross Amounts Recognized	1	232
Net Amount Presented	1	232
Notes receivable and other long-term assets, net | Fueling agreements
Derivative Assets
Gross Amounts Recognized	125	491
Net Amount Presented	125	491
Accrued liabilities | Fueling agreements
Derivative Liability
Gross Amounts Recognized	941	42
Net Amount Presented	941	42
Other long-term liabilities | Fueling agreements
Derivative Liability
Gross Amounts Recognized	1,261	39
Net Amount Presented	$ 1,261	$ 39

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities - Schedule of Weighted-Average Price of Open Commodity Wwap Contracts (Details) - Not Designated as Hedging Instrument	9 Months Ended	12 Months Ended
	Sep. 30, 2020$ / galgal	Dec. 31, 2019$ / galgal
Commodity Swap 2020
Derivative [Line Items]
Volumes (Diesel Gallons) | gal	1,250,000	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 - Commo

Fair Value Measurements - Commodity Swap Contracts (Details) - Not Designated as Hedging Instrument - Valuation Technique, Discounted Cash Flow - Level 3	Sep. 30, 2020	Dec. 31, 2019
Commodity swaps | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.26	1.76
Commodity swaps | Minimum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.81	0.79
Commodity swaps | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.42	1.32
Commodity swaps | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.44	1.88
Commodity swaps | Maximum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.58	1.16
Commodity swaps | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.58	2.30
Commodity swaps | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.38	1.81
Commodity swaps | Weighted Average | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.98	0.91
Commodity swaps | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.98	1.78
Fueling agreements | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.26	1.76
Fueling agreements | Minimum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.81	0.79
Fueling agreements | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.42	1.32
Fueling agreements | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.44	1.88
Fueling agreements | Maximum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.58	1.16
Fueling agreements | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.58	2.30
Fueling agreements | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.38	1.81
Fueling agreements | Weighted Average | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.98	0.91
Fueling agreements | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.98	1.78

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Available-for-sale securities	$ 530	$ 56,929
Short-term investments	530	56,929
Municipal bonds and notes
Assets:
Available-for-sale securities		2,986
Zero coupon bonds
Assets:
Available-for-sale securities		33,919
Corporate bonds
Assets:
Available-for-sale securities		19,506
Certificates of deposit
Assets:
Available-for-sale securities	530	518
Fair value measured on recurring basis | Municipal bonds and notes
Assets:
Available-for-sale securities		2,986
Fair value measured on recurring basis | Zero coupon bonds
Assets:
Available-for-sale securities		33,919
Fair value measured on recurring basis | Corporate bonds
Assets:
Available-for-sale securities		19,506
Fair value measured on recurring basis | Certificates of deposit
Assets:
Short-term investments	530	518
Fair value measured on recurring basis | Commodity swap contracts
Assets:
Derivative assets	9,839	3,270
Liabilities:
Derivative liabilities		164
Fair value measured on recurring basis | Embedded derivatives
Assets:
Derivative assets	126	723
Liabilities:
Derivative liabilities	2,202	81
Fair value measured on recurring basis | Warrants
Liabilities:
Derivative liabilities		40
Fair value measured on recurring basis | Level 2 | Municipal bonds and notes
Assets:
Available-for-sale securities		2,986
Fair value measured on recurring basis | Level 2 | Zero coupon bonds
Assets:
Available-for-sale securities		33,919
Fair value measured on recurring basis | Level 2 | Corporate bonds
Assets:
Available-for-sale securities		19,506
Fair value measured on recurring basis | Level 2 | Certificates of deposit
Assets:
Short-term investments	530	518
Fair value measured on recurring basis | Level 3 | Commodity swap contracts
Assets:
Derivative assets	9,839	3,270
Liabilities:
Derivative liabilities		164
Fair value measured on recurring basis | Level 3 | Embedded derivatives
Assets:
Derivative assets	126	723
Liabilities:
Derivative liabilities	$ 2,202	81
Fair value measured on recurring basis | Level 3 | Warrants
Liabilities:
Derivative liabilities		$ 40

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Recognition - Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income [Extensible List]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Commodity swap contracts
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	$ 9,743	$ 5,696	$ 3,270	$ 10,332
Settlements, net	(534)	1	(1,011)	210
Total gain (loss)	630	976	7,580	(3,869)
Ending balance	9,839	6,673	9,839	6,673
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	96	977	6,569	(3,659)
Embedded derivatives
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	94	450	723
Total gain (loss)	32	152	(597)	602
Ending balance	126	602	126	602
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 32	$ 152	$ (597)	$ 602

Fair Value Measurements - Fai_2

Fair Value Measurements - Fair Value Recognition - Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income [Extensible List]	Unrealized Gain (Loss) on Commodity Contracts	Unrealized Gain (Loss) on Commodity Contracts	Unrealized Gain (Loss) on Commodity Contracts	Unrealized Gain (Loss) on Commodity Contracts
Commodity swap contracts
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance			$ (164)
Settlements, net			56
Total gain (loss)			108
Change in unrealized gain (loss) included in earnings			164
Embedded derivatives
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance	$ (1,924)		(81)
Total gain (loss)	(278)		(2,121)
Ending Balance	(2,202)		(2,202)
Change in unrealized gain (loss) included in earnings	$ (278)		(2,121)
Warrants
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance		$ (2,676)	40	$ (1,079)
Total gain (loss)		10	40	(1,587)
Ending Balance		(2,666)		(2,666)
Change in unrealized gain (loss) included in earnings		$ 10	$ 40	$ (1,587)

Fair Value Measurements - (Deta

Fair Value Measurements - (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Asset transferred from level 1 to 2	$ 0	$ 0
Asset transferred from level 2 to 1	0	0
Asset transferred level 3 net	0	0
Liabilities transferred from level 1 to 2	0	0
Liabilities transferred from level 2 to 1	0	0
Liabilities transferred level 3 net	$ 0	$ 0

Other Receivables (Details)

Other Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Other Receivables
Other receivables	$ 23,152	$ 84,898
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	386	653
Accrued customer billings
Other Receivables
Other receivables	6,066	6,124
Fuel tax credits
Other Receivables
Other receivables	14,994	69,585
Other
Other Receivables
Other receivables	$ 1,706	$ 8,536

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials and spare parts	$ 28,830	$ 29,874
Total inventory	$ 28,830	$ 29,874

Land, Property and Equipment (D

Land, Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Land, Property and Equipment
Land, property and equipment, gross	$ 683,933		$ 683,933		$ 678,904
Less accumulated depreciation	(385,845)		(385,845)		(354,992)
Total land, property and equipment, net	298,088		298,088		323,912
Capitalized software costs, net	31,600		31,600		30,400
Accumulated amortization on the capitalized software costs	28,200		28,200		26,300
Amortization expense related to the capitalized software costs	600	$ 1,000	1,900	$ 3,100
Amount included in accounts payable balances			900	$ 2,200
Land
Land, Property and Equipment
Land, property and equipment, gross	3,476		3,476		3,476
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,633		94,633		94,633
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	347,636		347,636		324,431
Trailers
Land, Property and Equipment
Land, property and equipment, gross	79,670		79,670		79,477
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	86,921		86,921		101,655
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 71,597		$ 71,597		$ 75,232

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 14,738	$ 27,839
Accrued employee benefits	3,647	2,276
Accrued interest	310	220
Accrued gas and equipment purchases	9,724	11,383
Accrued property and other taxes	2,947	3,732
Accrued salaries and wages	7,711	9,105
Embedded derivatives	941	42
Other	10,184	13,100
Total accrued liabilities	$ 50,202	$ 67,697

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2013
Principal Balances
Total debt	$ 35,320	$ 89,094
Less amounts due within one year	(6,193)	(56,097)
Total long-term debt	29,127	32,997
Unamortized Debt Financing Costs
Total debt	147	209
Less amounts due within one year	(67)	(84)
Total long-term debt	80	125
Balance, Net of Financing Costs
Total debt	35,173	88,885
Less amounts due within one year	(6,126)	(56,013)
Total long-term debt	29,047	32,872
7.5% Notes
Principal Balances
Total debt		50,000
Unamortized Debt Financing Costs
Total debt		17
Balance, Net of Financing Costs
Total debt		$ 49,983
Interest rate		7.50%	7.50%
NG Advantage debt
Principal Balances
Total debt	30,057	$ 33,898
Unamortized Debt Financing Costs
Total debt	147	192
Balance, Net of Financing Costs
Total debt	29,910	33,706
SG Facility
Principal Balances
Total debt	4,700	4,400
Balance, Net of Financing Costs
Total debt	4,700	4,400
Other debt
Principal Balances
Total debt	563	796
Balance, Net of Financing Costs
Total debt	$ 563	$ 796

Debt - 7.5% Notes (Details)

Debt - 7.5% Notes (Details) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2020USD ($)	Jun. 30, 2013USD ($)D$ / shares	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)
Long-term debt [Line Items]
Amount of advance funded			$ 300	$ 3,694
Aggregate principal amount			$ 35,320			$ 89,094
7.5% Notes
Long-term debt [Line Items]
Interest rate		7.50%				7.50%
Debt issuance amount		$ 150,000
Conversion price of shares (in dollars per share) | $ / shares		$ 15.80
Percentage of the trade price of common stock that the conversion price must be at premium for the Company to force conversion		40.00%
Number of days within 30 consecutive trading days in which the trade price of the entity's common stock must be at premium of the conversion price for the Company to force conversion | D		20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion | D		30
Repayments of debt	$ 50,000
Aggregate principal amount						$ 50,000
7.5% Notes | Green Energy Investment Holdings, LLC
Long-term debt [Line Items]
Principal amount transferred					$ 16,800
Aggregate principal amount						32,900
7.5% Notes | Mr. Pickens
Long-term debt [Line Items]
Repurchased face amount during period					$ 25,000
7.5% Notes | Other Third Parties
Long-term debt [Line Items]
Aggregate principal amount						$ 17,100

Debt - SG Credit and TOTAL Cred

Debt - SG Credit and TOTAL Credit Support Agreement (Details) - USD ($) $ in Thousands	Jan. 02, 2019	Sep. 30, 2020	Dec. 31, 2019
Long-term debt [Line Items]
Outstanding amount		$ 35,320	$ 89,094
SG Facility | Socit Gnrale
Long-term debt [Line Items]
Maximum borrowing capacity (up to)	$ 100,000
Commitment fee percentage	0.39%
Covenant for debt default	$ 20,000
Outstanding amount		$ 4,700
SG Facility | Socit Gnrale | London Interbank Offered Rate (LIBOR)
Long-term debt [Line Items]
Basis spread on variable rate	1.30%
SG Facility | Total Holdings USA Inc.
Long-term debt [Line Items]
Maximum borrowing capacity (up to)	$ 100,000
Interest rate per quarter	2.50%
Covenant for debt default	$ 20,000
SG Facility | Total Holdings USA Inc. | London Interbank Offered Rate (LIBOR)
Long-term debt [Line Items]
Basis spread on variable rate	1.00%

Debt - NG Advantage Debt and Fi

Debt - NG Advantage Debt and Financing Lease Obligations (Details) $ in Millions	Jan. 17, 2019USD ($)installment	Dec. 20, 2018USD ($)	Mar. 01, 2018USD ($)installment	Dec. 18, 2017USD ($)installment	Oct. 31, 2019USD ($)	Jan. 24, 2017USD ($)installment	Nov. 30, 2016USD ($)installment	May 12, 2016USD ($)installment
Compression Station
Long-term debt [Line Items]
Purchase price		$ 7
Sale leaseback transaction, term		5 years
Annual rate (as a percent)		12.00%
Sale leaseback transaction, monthly rental payments		$ 0.1
Sale leaseback transaction, rent expense		4.7
Sale leaseback transaction, rent expense, repayment of promissory note		$ 2
Compression Equipment
Long-term debt [Line Items]
Purchase price					$ 7.5
Proceeds from sale of equipment in sale-leaseback agreement					5.3
Security deposit held					$ 2.2
Sale leaseback transaction, term					5 years
Annual rate (as a percent)					10.47%
BoA | BoA MLA
Long-term debt [Line Items]
Interest rate				4.86%
Proceeds from sale of equipment in sale-leaseback agreement				$ 2.1
Sale leaseback transaction, term				5 years
Number of equal monthly installments | installment				60
First National | First National MLA
Long-term debt [Line Items]
Interest rate			9.28%
Net proceeds, financing activities			$ 6.3
Sale leaseback transaction, term			6 years
Number of equal monthly installments | installment			72
Nations Fund I, LLC | Nations MLA
Long-term debt [Line Items]
Interest rate	9.18%
Proceeds from sale of equipment in sale-leaseback agreement	$ 3.4
Sale leaseback transaction, term	4 years
Number of equal monthly installments | installment	48
Loan and Security Agreement [Member] | 4.41% Term Loan | Commerce Bank & Trust Company
Long-term debt [Line Items]
Debt issuance amount								$ 6.3
Number of monthly installments | installment								84
Interest rate								4.41%
Loan and Security Agreement [Member] | 5.0% Term Loan | Commerce Bank & Trust Company
Long-term debt [Line Items]
Debt issuance amount						$ 6.2
Number of monthly installments | installment						84
Interest rate						5.00%
Loan and Security Agreement [Member] | 5.17% Term Loan | Wintrust Commercial Finance
Long-term debt [Line Items]
Debt issuance amount							$ 4.7
Number of monthly installments | installment							72
Interest rate							5.17%

Debt - Other Debt (Details)

Debt - Other Debt (Details)	Sep. 30, 2020
Other debt | Maximum
Long-term debt [Line Items]
Interest rate	4.75%

Net Income (Loss) Per Share (De

Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss attributable to Clean Energy Fuels Corp.	$ (2,271)	$ (4,334)	$ (7,303)	$ (20,663)
Weighted average common shares outstanding	198,785,394	204,712,888	201,472,851	204,522,984
Weighted average common shares outstanding - diluted	198,785,394	204,712,888	201,472,851	204,522,984
Basic and diluted loss per share	$ (0.01)	$ (0.02)	$ (0.04)	$ (0.10)

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Loss Per Share
Anti-dilutive securities (in shares)	10,423,191	14,473,832	11,909,609	14,473,832
Stock options
Net Loss Per Share
Anti-dilutive securities (in shares)	9,434,211	10,051,402	9,434,211	10,051,402
Convertibles notes
Net Loss Per Share
Anti-dilutive securities (in shares)		3,164,557	1,486,418	3,164,557
Restricted stock units
Net Loss Per Share
Anti-dilutive securities (in shares)	988,980	1,257,873	988,980	1,257,873

Stock-Based Compensation (Detai

Stock-Based Compensation (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense, net of $0 tax in 2018 and 2019		$ 708,000	$ 892,000	$ 2,522,000	$ 3,056,000
Stock-based compensation expense, tax		0	$ 0	0	$ 0
Unrecognized compensation cost		$ 3,300,000		$ 3,300,000
Unrecognized compensation cost, weighted-average period				1 year 6 months
Amended 2016 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in the aggregate number of shares	17,500,000

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Mar. 12, 2020
Equity [Abstract]
Approved share repurchase program					$ 30,000
Repurchase of common stock	$ 3,013	$ 6,406	$ 4,244	$ 13,500
Repurchase of common stock (in shares)				7,347,691
Repurchase of common stock				$ 13,663

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax expense	$ 79	$ 68	$ 235	$ 194
Unrecognized tax benefits, increase from portion of AFTC revenue offset by the fuel tax			$ 1,700

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases
Sales-type lease, interest income	$ 0.1	$ 0	$ 0.4	$ 0.1

Leases - Maturities of Lease Re

Leases - Maturities of Lease Receivables (Details) $ in Thousands	Sep. 30, 2020USD ($)
Fiscal year:
Remainder of 2020	$ 350
2021	1,402
2022	1,182
2023	962
2024	962
Thereafter	4,320
Total minimum lease payments	9,178
Less amount representing interest	(2,472)
Present value of lease receivables	$ 6,706

Alternative Fuel Excise Tax Cre

Alternative Fuel Excise Tax Credit (Details) $ in Millions	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2020USD ($)$ / gal	Dec. 31, 2019$ / gal
Alternative Fuel Excise Tax Credit
Federal alternative fuels tax credit - CNG (in dollars per gasoline gallon equivalent)			0.50	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 | $	$ 5	$ 47.1	$ 14.8

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
TOTAL S.E.
Related Party Transaction [Line Items]
Proceeds from related party	$ 2.6	$ 0	$ 5.3	$ 1.7
Receivables from related party	1		1		$ 0
Related party expense	0.1	0.4	0.5	0.9
SAFE&CEC S.r.l.
Related Party Transaction [Line Items]
Proceeds from related party	0.2	0	1.2	0.2
Receivables from related party	0.1		0.1		0.9
Related party expense	1.5	$ 0.6	4.3	$ 2.1
Payable to related parties	$ 0.5		$ 0.5		$ 0.8