Clean Energy Fuels (CLNE) 10-K 24 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 18, 2022	Jun. 30, 2021
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2021
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		222,503,640
Entity Public Float			$ 1,793,811,286
Auditor Name	KPMG LLP
Auditor Firm ID	185
Auditor Location	Irvine, California
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001368265
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 99,448	$ 108,977
Short-term investments	129,722	29,528
Accounts receivable, net of allowance of $1,335 and $1,205 as of December 31, 2020 and 2021, respectively	87,433	61,784
Other receivables	24,447	23,655
Inventory	31,302	28,100
Prepaid expenses and other current assets	37,584	9,404
Derivative assets, related party		1,591
Total current assets	409,936	263,039
Operating lease right-of-use assets	42,537	25,967
Land, property and equipment, net	261,761	290,911
Restricted cash	7,008	11,000
Notes receivable and other long-term assets, net	56,189	27,299
Long-term portion of derivative assets, related party		4,057
Investments in other entities	109,811	27,962
Goodwill	64,328	64,328
Intangible assets, net	5,500	464
Total assets	957,070	715,027
Current liabilities:
Current portion of debt	12,845	3,592
Current portion of finance lease obligations	846	840
Current portion of operating lease obligations	3,551	2,822
Accounts payable	24,352	17,310
Accrued liabilities	75,159	52,637
Deferred revenue	7,251	2,642
Derivative liabilities, related party	1,900
Total current liabilities	125,904	79,843
Long-term portion of debt	23,215	82,088
Long-term portion of finance lease obligations	2,427	2,552
Long-term portion of operating lease obligations	39,431	23,698
Long-term portion of derivative liabilities, related party	2,483
Other long-term liabilities	8,199	3,996
Total liabilities	201,659	192,177
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 and 454,000,000 shares authorized; 198,491,204 shares and 222,684,923 shares issued and outstanding as of December 31, 2020 and 2021, respectively	22	20
Additional paid-in capital	1,519,918	1,191,791
Accumulated deficit	(771,242)	(678,096)
Accumulated other comprehensive loss	(1,622)	(209)
Total Clean Energy Fuels Corp. stockholders' equity	747,076	513,506
Noncontrolling interest in subsidiary	8,335	9,344
Total stockholders' equity	755,411	522,850
Total liabilities and stockholders' equity	$ 957,070	$ 715,027

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,205	$ 1,335
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)	454,000,000	304,000,000
Common stock, issued (in shares)	222,684,923	198,491,204
Common stock, outstanding (in shares)	222,684,923	198,491,204

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues [Abstract]
Total revenue	$ 255,646	$ 291,724	$ 344,065
Cost of sales (exclusive of depreciation and amortization shown separately below):
Change in fair value of derivative warrants		(40)	(1,039)
Selling, general and administrative	89,906	68,516	73,444
Depreciation and amortization	45,184	47,682	49,625
Total operating expenses	350,694	301,568	334,137
Operating income (loss)	(95,048)	(9,844)	9,928
Interest expense	(4,430)	(7,348)	(7,574)
Interest income	1,082	1,345	2,437
Other income, net	905	3,025	1,990
Loss from equity method investments	(430)	(161)	(119)
Gain from sale of certain assets of subsidiary	3,885	1,063	7,455
Gain from formation of equity method investment		700
Income (loss) before income taxes	(94,036)	(11,220)	14,117
Income tax expense	(119)	(309)	(858)
Net income (loss)	(94,155)	(11,529)	13,259
Loss attributable to noncontrolling interest	1,009	1,665	7,162
Net income (loss) attributable to Clean Energy Fuels Corp.	$ (93,146)	$ (9,864)	$ 20,421
Net loss attributable to Clean Energy Fuels Corp. per share:
Basic (in dollars per share)	$ (0.44)	$ (0.05)	$ 0.10
Diluted (in dollars per share)	$ (0.44)	$ (0.05)	$ 0.10
Weighted-average common shares outstanding:
Basic (in shares)	213,118,694	200,657,912	204,573,287
Diluted (in shares)	213,118,694	200,657,912	205,987,509
Product revenue
Revenues [Abstract]
Total revenue	$ 213,133	$ 251,954	$ 298,469
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	189,600	161,705	185,557
Service revenue
Revenues [Abstract]
Total revenue	42,513	39,770	45,596
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	$ 26,004	$ 23,705	$ 26,550

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (loss)	$ (94,155)	$ (11,529)	$ 13,259
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments net of $0 tax in 2019, 2020 and 2021	(1,394)	1,355	505
Unrealized gains on available-for-sale securities, net of $0 tax in 2019, 2020 and 2021	(19)	2	67
Total other comprehensive income (loss)	(1,413)	1,357	572
Comprehensive income (loss)	(95,568)	(10,172)	13,831
Clean Energy Fuels Corp.
Net income (loss)	(93,146)	(9,864)	20,421
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments net of $0 tax in 2019, 2020 and 2021	(1,394)	1,355	505
Unrealized gains on available-for-sale securities, net of $0 tax in 2019, 2020 and 2021	(19)	2	67
Total other comprehensive income (loss)	(1,413)	1,357	572
Comprehensive income (loss)	(94,559)	(8,507)	20,993
Noncontrolling Interest in Subsidiary
Net income (loss)	(1,009)	(1,665)	(7,162)
Other comprehensive income (loss), net of tax:
Comprehensive income (loss)	$ (1,009)	$ (1,665)	$ (7,162)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustment, tax	$ 0	$ 0	$ 0
Unrealized gains on available-for sale securities, tax	$ 0	$ 0	$ 0

CONSOLIDATED STATEMENTS OF STOC

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, net of offering costs		309				309
Issuance of common stock, net of offering costs (in shares)	1,123,163
Stock-based compensation		3,880				3,880
Net income (loss)			20,421		(7,162)	13,259
Other comprehensive income (loss)				572		572
Increase in ownership in subsidiary		228			(228)
Ending balance at Dec. 31, 2019	$ 20	1,203,186	(668,232)	(1,566)	9,621	543,029
Ending balance (in shares) at Dec. 31, 2019	204,723,055
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs	$ 0	1,683				1,683
Issuance of common stock, net of offering costs (in shares)	1,512,535
Repurchase of common stock		(14,647)				(14,647)
Repurchase of common stock (in shares)	(7,744,386)
Stock-based compensation		2,957				2,957
Net income (loss)			(9,864)		(1,665)	(11,529)
Other comprehensive income (loss)				1,357		1,357
Increase in ownership in subsidiary		(1,388)			1,388
Ending balance at Dec. 31, 2020	$ 20	1,191,791	(678,096)	(209)	9,344	$ 522,850
Ending balance (in shares) at Dec. 31, 2020	198,491,204					198,491,204
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs	$ 2	197,919				$ 197,921
Issuance of common stock, net of offering costs (in shares)	24,646,419
Repurchase of common stock		(2,916)				$ (2,916)
Repurchase of common stock (in shares)	(452,700)					(452,700)
Stock-based compensation		14,994				$ 14,994
Stock-based sales incentive charges		118,130				118,130
Net income (loss)			(93,146)		(1,009)	(94,155)
Other comprehensive income (loss)				(1,413)		(1,413)
Ending balance at Dec. 31, 2021	$ 22	$ 1,519,918	$ (771,242)	$ (1,622)	$ 8,335	$ 755,411
Ending balance (in shares) at Dec. 31, 2021	222,684,923					222,684,923

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (94,155)	$ (11,529)	$ 13,259
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	45,184	47,682	49,625
Provision for credit losses and inventory	1,257	2,662	2,586
Stock-based compensation expense	14,994	2,957	3,880
Stock-based sales incentive charges	83,641	0	0
Change in fair value of derivative instruments	3,490	(2,175)	5,545
Amortization of discount and debt issuance cost	20	(46)	(728)
Loss (gain) on disposal of property and equipment	1,365	(2,875)	(2,536)
Loss on extinguishment of debt	39	1,249
Gain from sale of certain assets of subsidiary	(3,885)	(1,063)	(7,455)
Gain from formation of equity method investment		(700)
Loss from equity method investments	430	161	119
Non-cash lease expense	2,945	2,756	3,234
Deferred income taxes	69	120	738
Expense reimbursement from JV	1,640
Changes in operating assets and liabilities:
Accounts and other receivables	(24,260)	53,784	(63,408)
Inventory	(5,704)	108	3,439
Prepaid expenses and other assets	(10,498)	5,275	(16,617)
Operating lease liabilities	(3,053)	(3,141)	(3,786)
Accounts payable	6,615	(9,337)	9,316
Deferred revenue	4,550	(10,976)	(3,528)
Accrued liabilities and other	16,614	(13,871)	18,596
Net cash provided by operating activities	41,298	61,041	12,279
Cash flows from investing activities:
Purchases of short-term investments	(324,170)	(74,292)	(171,080)
Maturities and sales of short-term investments	223,991	101,850	180,704
Purchases of and deposits on property and equipment	(23,075)	(13,273)	(27,088)
Disbursements for loans receivable for RNG production projects	(3,905)	(535)
Payments on and proceeds from sales of loans receivable	421	1,567	608
Cash received from sale of certain assets of subsidiary, net	887	4,830	7,582
Investments in other entities	(78,919)	(650)
Payment and deposits on equipment and manure rights for RNG production projects	(5,830)
Proceeds from disposal of property and equipment	2,941	4,673	7,772
Net cash provided by (used in) investing activities	(207,659)	24,170	(1,502)
Cash flows from financing activities:
Issuance of common stock	204,455	1,683	309
Repurchase of common stock	(2,916)	(14,647)
Fees paid for issuance of common stock	(6,534)
Fees paid for debt issuance costs	(1,277)	(131)	(123)
Proceeds for Adopt-a-Port program	5,815
Repayment of proceeds for Adopt-a-Port program	(360)
Proceeds from debt instruments	4,400	65,860	15,294
Proceeds from revolving line of credit	1,450
Repayments of borrowing under revolving line of credit	(1,450)
Repayments of debt instruments and finance lease obligations	(50,737)	(70,399)	(7,795)
Payments of debt extinguishment costs	(14)	(1,023)
Net cash (used in) provided by financing activities	152,832	(18,657)	7,685
Effect of exchange rates on cash, cash equivalents and restricted cash	8	201	136
Net increase (decrease) in cash, cash equivalents and restricted cash	(13,521)	66,755	18,598
Cash, cash equivalents and restricted cash, beginning of period	119,977	53,222	34,624
Cash, cash equivalents and restricted cash, end of period	106,456	119,977	53,222
Supplemental disclosure of cash flow information:
Income taxes paid	15	8	36
Interest paid, net of $441, $57 and $0 capitalized, respectively	$ 3,907	$ 5,622	$ 6,788

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Cash Flows [Abstract]
Interest paid, capitalized	$ 0	$ 57	$ 441

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Significant Accounting Policies	Note 1 —Summary of Significant Accounting Policies The Company and 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”) and conventional natural gas, in the form of compressed natural gas (“CNG”) and liquefied natural gas (“LNG”), for medium and heavy-duty vehicles and providing operation and maintenance (“O&M”) services for public and private vehicle fleet customer stations. The Company is also focused on developing, owning, and operating dairy and other livestock waste RNG projects and supplying RNG (procured from our own projects or from third parties) to its customers in the heavy and medium-duty commercial transportation sector. As a comprehensive clean energy solutions provider, the Company also designs and builds, as well as operates and maintains, public and private vehicle fueling stations in the United States and Canada; sells and services compressors and other equipment used in RNG production and at fueling stations; transports and sells CNG and LNG via “virtual” natural gas pipelines and interconnects; sells U.S. federal, state and local government credits it generates by selling RNG 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”); and obtains federal, state and local tax credits, grants and incentives. Basis of Presentation The accompanying 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, results of operations, comprehensive income (loss) and cash flows in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying 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 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, stock-based compensation expense and stock-based sales incentive charges. Inventory Inventory consists of raw materials and spare parts, work in process and finished goods and is stated at the lower of cost (first-in, first-out) or net realizable value. The Company evaluates inventory balances for excess quantities and obsolescence by analyzing estimated demand, inventory on hand, sales levels and other information and reduces inventory balances to net realizable value for excess and obsolete inventory based on this analysis. ​ Inventories consisted of the following as of December 31, 2020 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Raw materials and spare parts ​ $ 28,100 ​ $ 31,302 Total inventory ​ $ 28,100 ​ $ 31,302 ​ Derivative Instruments and Hedging Activities In connection with the Company’s Zero Now Zero Now Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization are recognized over the estimated useful lives of the assets using the straight-line method. The estimated useful lives of depreciable assets are three LNG trailers three Leases On January 1, 2019, the Company adopted Accounting Standards Codification (“ASC”) 842, Leases At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether the Company obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether the Company has the right to direct the use of the asset. The commencement date of the contract is the date the lessor makes the underlying asset available for use by the lessee. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less; the Company recognizes lease expense for these leases on a straight-line basis over the lease term. As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease. The lease classification affects the expense recognition on the consolidated statements of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, whereby depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting. Long-Lived Assets The Company reviews the carrying value of its long-lived assets, including property and equipment and intangible assets with finite useful lives, for impairment whenever events or changes in circumstances indicate that the carrying value of an asset or asset group may not be recoverable. Events that could result in an impairment review include, among others, a significant decrease in the operating performance of a long-lived asset or asset group or the decision to close a fueling station. Impairment testing involves a comparison of the sum of the undiscounted future cash flows of the asset or asset group to its carrying amount. If the sum of the undiscounted future cash flows exceeds the carrying amount, then no impairment exists. If the carrying amount exceeds the sum of the undiscounted future cash flows, then a second step is performed to determine the amount of impairment, if any, to be recognized. An impairment loss is recognized to the extent that the carrying amount of the asset or asset group exceeds its fair value. The fair value of the asset or asset group is based on estimated discounted future cash flows of the asset or asset group using a discount rate commensurate with the related risk. The estimate of future cash flows requires management to make assumptions and to apply judgment, including forecasting future sales and expenses and estimating useful lives of the assets. These estimates can be affected by a number of factors, including, among others, future results, demand, and economic conditions, many of which can be difficult to predict. There were no impairments of the Company’s long-lived assets in the years ended December 31, 2019, 2020 and 2021. Intangible assets with finite useful lives are amortized over their respective estimated useful lives using the straight-line method. The estimated useful lives of intangible assets with finite useful lives are from one one two The Company’s intangible assets as of December 31, 2020 and 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Customer relationships ​ $ 5,376 ​ $ 5,376 Acquired contracts ​ 4,384 ​ 9,884 Trademark and trade names ​ 2,700 ​ 2,700 Non-compete agreements ​ 860 ​ 860 Total intangible assets ​ 13,320 ​ 18,820 Less accumulated amortization ​ (12,856) ​ (13,320) Net intangible assets ​ $ 464 ​ $ 5,500 ​ Amortization expense for intangible assets was $1.0 million, $0.8 million, and $0.5 million for the years ended December 31, 2019, 2020, and 2021, respectively. In 2021, the Company acquired contractual rights to manure feedstock for an anaerobic digester gas (“ADG”) RNG production project totaling $5.5 million. The acquired manure rights have an initial term of 20 years. Amounts are classified and included under “Acquired contracts” in the table above. As of December 31, 2021, the Company paid $1.0 million and accrued $4.5 million, which was included in “Accrued liabilities” in the accompanying consolidated balance sheets, related to the acquired manure rights. The $4.5 million was excluded from the accompanying consolidated statements of cash flows as it was a non-cash investing activity. The intangible asset related to manure rights will be amortized over the contractual term of 20 years using the straight-line method with amortization commencing on the date of commercial operation of the ADG RNG facility. Estimated amortization expense subsequent to the year ended December 31, 2021 is expected to be approximately $0.0 million in 2022, $0.0 million in 2023, $0.3 million in 2024, $0.3 million in 2025, $0.3 million in 2026, and $4.6 million thereafter. Goodwill Goodwill represents the excess of costs incurred over the fair value of the net assets of acquired businesses. The Company assesses its goodwill using either a qualitative or quantitative approach to determine whether it is more likely than not that the fair value of its reporting unit is less than its carrying value. The Company is required to use judgment when applying the goodwill impairment test, including, among other considerations, the identification of reporting unit(s), the assessment of qualitative factors, and the estimation of fair value of a reporting unit in the quantitative approach. The Company determined that it is a single reporting unit for the purpose of goodwill impairment tests. The Company performs the impairment test annually on October 1, or more frequently if facts and circumstances warrant a review. The qualitative goodwill assessment includes the potential impact on a reporting unit’s fair value of certain events and circumstances, including its enterprise value, macroeconomic conditions, industry and market considerations, cost factors, and other relevant entity-specific events. If it is determined, based upon the qualitative assessment, that it is more likely than not that the reporting unit’s fair value is less than its carrying amount, then a quantitative impairment test is performed. The quantitative assessment estimates the reporting unit’s fair value based on its enterprise value plus an assumed control premium as evidence of fair value. The estimates used to determine the fair value of the reporting unit may change based on results of operations, macroeconomic conditions, stock price fluctuations, or other factors. Changes in these estimates could materially affect our assessment of the fair value and goodwill impairment for the reporting unit. During the years ended The following table summarizes the activity related to the carrying amount of goodwill (in thousands): ​ ​ ​ ​ Balance as of December 31, 2019 ​ $ 64,328 Balance as of December 31, 2020 ​ $ 64,328 Balance as of December 31, 2021 ​ $ 64,328 ​ Revenue Recognition ​ 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 them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities. ​ Volume-Related The Company’s volume-related revenue primarily consists of sales of RNG and conventional natural gas, in the form of CNG and LNG, O&M services and RINs and LCFS Credits in addition to Amazon Warrant Charges and changes in fair value of the Company’s derivative instruments associated with providing fuel to customers under contracts. Fuel and O&M services are sold pursuant to contractual commitments over defined goods-and-service delivery periods. These contracts typically include a stand-ready obligation to supply natural gas and/or provide O&M services daily based on a committed and agreed upon routine maintenance schedule or when and if called upon by the customer. The Company applies the ‘right to invoice’ practical expedient and recognizes fuel and O&M services revenue in the amount to which the Company has the right to invoice. The Company has a right to consideration based on the amount of gasoline gallon equivalents of fuel dispensed by the customer and current pricing conditions, which are typically billed to the customer on a monthly basis. Since payment terms are less than a year, the Company has elected the practical expedient which allows it to not assess whether a customer contract has a significant financing component. Contract modifications are not distinct from the existing contract and are typically renewals of fuel and O&M service sales. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price is recognized prospectively. The Company sells RINs and LCFS Credits to third parties that need the credits to comply with federal and state requirements. Revenue is recognized on these credits when there is an agreement in place to monetize the credits at a determinable price. Amazon Warrant Charges (defined in Note 13) are determined based on the grant date fair value of the award and the associated non-cash stock-based sales incentive charges, which are recorded as a reduction of revenue and are recognized as the customer purchases fuel and vesting conditions become probable of being achieved. See discussion under “Amazon Warrant” below and Note 13 for additional information. The changes in fair value of derivative instruments relate to the Company’s commodity swap and customer fueling contracts. The contracts are measured at fair value with changes in fair value recorded in the accompanying consolidated statements of operations in the period incurred. 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 existing and anticipated customer fueling contracts under the Company’s Zero Now Station Construction Sales Station construction contracts are generally short-term, except for certain larger and more complex stations, which can take up to 24 months to complete. For most of the Company’s station construction contracts, the customer contracts with the Company to provide a significant service of integrating a complex set of tasks and components into a single station. Hence, the entire contract is accounted for as one performance obligation. The Company recognizes revenue over time as the Company performs under its station construction contracts because of the continual transfer of control of the goods to the customer, who typically controls the work in process. Revenue is recognized based on the extent of progress towards completion of the performance obligation and is recorded proportionally as costs are incurred. Costs to fulfill the Company’s obligations under these contracts typically include labor, materials and subcontractors’ costs, other direct costs and an allocation of indirect costs. Refinements of estimates to account for changing conditions and new developments are continuous and characteristic of the process. Many factors that can affect contract profitability may change during the performance period of the contract, including differing site conditions, the availability of skilled contract labor, the performance of major suppliers and subcontractors, and unexpected changes in material costs. Because a significant change in one or more of these estimates could affect the profitability of these contracts, the contract price and cost estimates are reviewed periodically as work progresses and adjustments proportionate to the cost-to-cost measure of progress are reflected in contract revenues in the reporting period when such estimates are revised. Provisions for estimated losses on uncompleted contracts are recorded in the period in which the losses become known. Contract modifications are typically expansions in scope of an existing station construction project. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price and the Company’s measure of progress for the performance obligation to which it relates is recognized as an adjustment to revenue (either as an increase or a reduction) on a cumulative catch-up basis. Under the typical payment terms of the Company’s station construction contracts, the customer makes either performance-based payments (“PBPs”) or progress payments. PBPs are interim payments of the contract price based on quantifiable measures of performance or the achievement of specified events or milestones. Progress payments are interim payments of costs incurred as the work progresses. For some of these contracts, the Company may be entitled to receive an advance payment. The advance payment typically is not considered a significant financing component because it is used to meet working capital demands that can be higher in the early stages of a construction contract and to protect the Company if the customer fails to adequately complete some or all of its obligations under the contract. In addition, the customer retains a small portion of the contract price until completion of the contract. Such retained portion of the contract price is not considered a significant financing component because the intent is to protect the customer. In certain contracts with its customers, the Company agrees to provide multiple goods or services, including construction of and sale of a station, O&M services, and sale of fuel to the customer. These contracts have multiple performance obligations because the promise to transfer each separate good or service is separately identifiable and is distinct. This evaluation requires significant judgment and the decision to combine a group of contracts or separate the combined or single contract into multiple performance obligations could change the amount of revenue recognized in one or more periods. The Company allocates the contract price to each performance obligation using best estimates of the standalone selling price of each distinct good or service in the contract. The primary method used to estimate the standalone selling price for fuel and O&M services is observable standalone sales, and the primary method used to estimate the standalone selling price for station construction sales is the expected cost plus a margin approach because the Company sells customized customer-specific solutions. Under this approach, the Company forecasts expected costs of satisfying a performance obligation and then adds an appropriate margin for the good or service. ​ AFTC See discussion under “Alternative Fuel Tax Credit” below for more information about AFTC, which is not recognized as revenue until the period the credit is authorized through federal legislation. Other The majority of other revenue is from sales of used natural gas heavy-duty trucks purchased by the Company. Revenue on these contracts is recognized at the point in time when the customer accepts delivery of the truck. ​ Alternative Fuel Tax Credit Under separate pieces of U.S. federal legislation, the Company has been eligible to receive a federal alternative fuels tax credit (“AFTC”) for its natural gas vehicle fuel sales made between October 1, 2006 and December 31, 2021. The AFTC, which had previously expired on December 31, 2016, was reinstated on February 9, 2018 to apply retroactively to vehicle fuel sales made from January 1, 2017 through December 31, 2017. On December 20, 2019, AFTC was retroactively extended beginning January 1, 2018 through December 31, 2020 and subsequently extended for vehicle fuel sales made through December 31, 2021. As a result of the 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 year ended December 31, 2019. AFTC was extended in December 2020 and is currently available for vehicle fuel sales made through December 31, 2021. The AFTC credit is equal to $0.50 per gasoline gallon equivalent of CNG that the Company sold as vehicle fuel, and $0.50 per diesel gallon of LNG that the Company sold as vehicle fuel in 2019, 2020 and 2021. Based on the service relationship with its customers, either the Company or its customer claims the credit. The Company records its AFTC credits, if any, as revenue in its consolidated statements of operations because the credits are fully payable to the Company and do not offset income tax liabilities. As such, the credits are not deemed income tax credits under the accounting guidance applicable to income taxes. LNG Transportation Costs The Company records the costs incurred to transport LNG to its customers in “Product cost of sales” in the accompanying consolidated statements of operations. Advertising Costs Advertising costs are expensed as incurred. Advertising costs were $1.2 million, $0.0 million and $0.0 million for the years ended December 31, 2019, 2020 and 2021, respectively. Stock-Based Compensation The Company recognizes compensation expense for all stock‑based payment arrangements over the requisite service period of the award and recognizes forfeitures as they occur. For stock options, the Company determines the grant date fair value using the Black‑Scholes option pricing model, which requires the input of certain assumptions, including the expected life of the stock‑based payment award, stock price volatility and risk‑free interest rate. For restricted stock units, the Company determines the grant date fair value based on the closing market price of its common stock on the date of grant. Amazon Warrant The Amazon Warrant (as defined in Note 13) is accounted for as an equity instrument and measured in accordance with Accounting Standards Codification (“ASC”) 718, Compensation – Stock Compensation the transaction price in accordance with ASC 606, Revenue from Contracts with Customers Income Taxes Income taxes are computed using the asset and liability method. Under this method, deferred income taxes are recognized by applying enacted statutory tax rates applicable to future years to differences between the tax bases and financial carrying amounts of existing assets and liabilities. The impact on deferred taxes of changes in tax rates and laws, if any, are applied to the years during which temporary differences are expected to be settled and are reflected in the consolidated financial statements in the period of enactment. Valuation allowances are established when management determines it is more likely than not that deferred tax assets will not be realized. When evaluating the need for a valuation analysis, we use estimates involving a high degree of judgment including projected future US GAAP income and the amounts and estimated timing of the reversal of any deferred tax assets and liabilities. The Company has a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities based on the technical merits of the position. The amount recognized is measured as the largest amount of benefit that has a greater than 50 percent likelihood of being realized upon ultimate settlement. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefit in income tax expense. The Company operates within multiple domestic and foreign taxing jurisdictions and is subject to audit in these jurisdictions. These audits can involve complex issues, which may require an extended period of time to resolve. Although the Company believes that adequate consideration has been given to these issues, it is possible that the ultimate resolution of these issues could be significantly different from originally estimated. 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. Foreign Currency Translation and Transactions The Company uses the local currency as the functional currency of its foreign subsidiary and equity method investment. Accordingly, all assets and liabilities outside the United States are translated into U.S. dollars at the rate of exchange in effect at the balance sheet date. Revenue and expense items are translated at the weighted-average exchange rates prevailing during the period. Foreign currency translation adjustments are recorded as accumulated other comprehensive income (loss) in stockholders’ equity. Foreign currency transactions occur when there is a transaction denominated in other than the respective entity’s functional currency. The Company records the changes in the exchange rate for these transactions in its consolidated statements of operations. For each of the years ended December 31, 2019, 2020 and 2021, foreign exchange transaction gains and (losses) were included in “Other income (expense), net” in the accompanying consolidated statements of operations and were $0.0 million. Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity (net assets) of a business enterprise during the period from transactions and other events and circumstances from non-owner sources. The difference between net income (loss) and comprehensive income (loss) for the years ended December 31, 2019, 2020 and 2021 was comprised of the Company’s foreign currency translation adjustments and unrealized gains and losses on available-for-sale securities. Concentration of Credit Risk Credit is extended to all customers based on financial condition, and collateral is generally not required. Concentrations of credit risk with respect to trade receivables are limited because of the large number of customers comprising the Company’s customer base and dispersion across many different industries and geographies. Certain international customers, however, have historically been slower to pay on trade receivables. Accordingly, the Company continually monitors collections and payments from its customers and maintains a provision for estimated credit losses based upon its historical experience and any specific customer collection issues that it has identified. Although credit losses have historically been within the Company’s expectations and the provisions established, the Company cannot guarantee that it will continue to experience the same credit loss rates that it has in the past. Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Recently Issued Accounting Pronouncements In July 2021, the FASB issued ASU No. 2021-05, Leases (Topic 842): Lessors–Certain Leases with Variable Lease Payments In November 2021, the FASB issued ASU No. 2021-10, Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance 15, 2021, with early adoption permitted. The Company is currently evaluating the impact of adopting this new ASU and does not expect the update to have a material impact on its consolidated financial statements and related disclosures.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Note 2 —Revenue from Contracts with Customers Disaggregation of Revenue The table below presents the Company’s revenue disaggregated by revenue source (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years Ended December 31, ​ 2019 2020 2021 Volume-related (1) (2) ​ $ 273,535 ​ $ 245,300 ​ $ 218,540 Station construction sales ​ 23,120 ​ 26,593 ​ 16,406 AFTC (3) ​ 47,123 ​ 19,831 ​ 20,700 Other ​ 287 ​ — ​ — Total revenue ​ $ 344,065 ​ $ 291,724 ​ $ 255,646 ​ (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. See Note 1 and Note 7 for more information about these derivative instruments. For the years ended December 31, 2019, 2020 and 2021, changes in the fair value of commodity swaps and customer fueling contracts amounted to a loss of $6.6 million, a gain of $2.1 million, and a loss of $3.5 million, respectively. (2) Includes non-cash stock-based sales incentive contra-revenue charges associated with the Amazon Warrant for the years ended December 31, 2019, 2020 and 2021 of $0.0 million, $0.0 million and $83.6 million, respectively. See Note 13 for more information. (3) Represents the federal alternative fuel excise tax credit that we refer to as “AFTC,” which was extended for vehicle fuel sales made beginning January 1, 2021 through December 31, 2021. Remaining Performance Obligations Remaining performance obligations represent the transaction price of customer orders for which the work has not been performed. As of December 31, 2021, the aggregate amount of the transaction price allocated to remaining performance obligations was $19.8 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 ‘ Costs to Fulfill a Contract The Company capitalizes costs incurred to fulfill its contracts that (1) relate directly to the contract, (2) are expected to generate resources that will be used to satisfy the Company’s performance obligations under the contract, and (3) are expected to be recovered through revenue generated under the contract. Contract fulfillment costs are recorded to depreciation expense as the Company satisfies its performance obligations over the term of the contract. These costs primarily relate to set-up and other direct installation costs incurred by NG Advantage, LLC (“NG Advantage”), for equipment that must be installed on customers’ land before NG Advantage is able to deliver CNG to the customer because the customer does not have direct access to the natural gas pipelines. These costs are classified in “Land, property, and equipment, net” in the accompanying consolidated balance sheets. As of December 31, 2020 and 2021, these capitalized costs incurred to fulfill contracts were $10.4 million and $10.1 million with accumulated depreciation of $7.1 million and $7.6 million, respectively, and related depreciation expense of $0.8 million and $0.5 million for the years ended December 31, 2020 and 2021, respectively. 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 consolidated balance sheets. Changes in the contract asset and liability balances during the year ended December 31, 2021, were not materially affected by any factors outside the normal course of business. As of December 31, 2020 and 2021, the Company’s contract balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 ​ ​ ​ ​ ​ ​ ​ Accounts receivable, net ​ $ 61,784 ​ $ 87,433 ​ ​ ​ ​ ​ ​ Contract assets - current ​ $ 729 ​ $ 966 Contract assets - non-current ​ 3,998 ​ 3,532 Contract assets - total ​ $ 4,727 ​ $ 4,498 ​ ​ ​ ​ ​ ​ Contract liabilities - current ​ $ 1,638 ​ $ 5,523 Contract liabilities - non-current ​ 59 ​ — Contract liabilities - total ​ $ 1,697 ​ $ 5,523 ​ Accounts Receivable, Net “Accounts receivable, net” in the accompanying consolidated balance sheets include amounts billed and currently due from customers. The amounts due are stated at their net estimated realizable value. The Company maintains an allowance 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 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 customers of NG Advantage in advance of the performance obligations and are classified as current or noncurrent based on when the 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 consolidated balance sheets. Billings in excess of revenue recognized of $1.0 million and $5.4 million and advance payments of $0.6 million and $0.1 million are classified as current as of December 31, 2020 and 2021, respectively. Revenue recognized during the year ended December 31, 2020 related to the Company’s contract liability balances as of December 31, 2019 was $4.8 million. The increase in the contract liability balances for the year ended December 31, 2021 was primarily driven by billings in excess of revenue recognized, offset by $1.5 million of revenue recognized related to the Company’s contract liability balances as of December 31, 2020.

Divestitures

Divestitures	12 Months Ended
	Dec. 31, 2021
Business Combinations [Abstract]
Divestitures	Note 3 —Divestitures bp Transaction On February 27, 2017, Clean Energy Renewable Fuels (“Renewables”) entered into an asset purchase agreement (the “APA”) with BP Products North America (“bp”). Pursuant to the APA, Renewables agreed to sell to bp its assets relating to its RNG production business (the “bp Transaction”), consisting of Renewables’ two RNG production facilities, Renewables’ interest in joint ventures formed with a third-party to develop new RNG production facilities, and Renewables’ third-party RNG supply contracts (the “Assets”). Under the APA, bp was required, following the closing of the bp Transaction, to pay Renewables up to an additional $25.0 million in cash over a five-year period if certain conditions relating to the Assets are met. In February 2018, the Company received $0.9 million in cash for its satisfaction of the performance criteria for the first period under the APA, which ended on December 31, 2017. Upon its receipt of such cash, the Company paid $0.1 million in cash and issued 15,877 shares of the Company’s common stock with a fair value of $0.0 million to former holders of options to purchase membership units in Renewables. The performance criteria for the second period under the APA, which ended on December 31, 2018, was also satisfied, and the Company received a cash payment of $5.4 million in March 2019. During the year ended December 31, 2019, after receipt of the cash payment, the Company paid $0.6 million in cash to former holders of options to purchase membership units in Renewables. In December 2019, the Company and bp entered into an Amendment to the APA (“Amended APA”) which amended the earn-out for years four five As of December 31, 2021, the Company has paid $10.3 million in cash and issued 770,269 shares of the Company’s common stock with a fair value of $2.0 million to former holders of options to purchase membership units in Renewables. Following the completion of the bp Transaction, Renewables and the Company continue to procure RNG from bp under a long-term supply contract (the “bp Supply Agreement”) and from other RNG suppliers and resell such RNG through the Company’s fueling infrastructure. On October 1, 2018, Renewables and bp amended the bp Supply Agreement to extend the term and add additional RNG supply. bp and Renewables share in the RINs and LCFS Credits generated from the increased RNG supply sold through the Company’s vehicle fueling infrastructure and to other customers. See Note 1 for information on revenue recognition of these credits. 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. At the closing of the CEC Combination on December 29, 2017, the Company owns 49% of SAFE&CEC S.r.l. and LR owns 51% of SAFE&CEC S.r.l. The Company accounts for its interest in SAFE&CEC S.r.l. using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over SAFE&CEC S.r.l.’s operations. The Company recorded income (loss) from this investment of $0.0 million, $(0.2) million and $0.6 million for the years ended December 31, 2019, 2020 and 2021, respectively. The Company had an investment balance in SAFE&CEC S.r.l. of $24.7 million and $23.9 million as of December 31, 2020 and 2021, respectively.

Investments in Other Entities a

Investments in Other Entities and Noncontrolling Interest in a Subsidiary	12 Months Ended
	Dec. 31, 2021
Investments, All Other Investments [Abstract]
Investments in Other Entities and Noncontrolling Interest in a Subsidiary	Note 4 —Investments in Other Entities and Noncontrolling Interest in a Subsidiary TotalEnergies Joint Venture ​ On March 3, 2021, the Company entered an agreement (“TotalEnergies JV Agreement”) with TotalEnergies S.E. (“TotalEnergies”) that created a 50/50 joint venture (“TotalEnergies JV”) to develop ADG RNG production facilities in the United States. Each ADG RNG production facility project under the TotalEnergies JV will be formed as a separate limited liability company (“LLC”) that is owned 50/50 by the Company and TotalEnergies, and contributions to such LLCs count toward the TotalEnergies JV Equity Obligations (as defined below). The TotalEnergies JV Agreement contemplates that the TotalEnergies JV will invest up to $400.0 million of equity in production projects, and TotalEnergies TotalEnergies TotalEnergies The following table presents combined summarized financial information for the TotalEnergies JV (in thousands): ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 Revenue ​ $ — Gross profit ​ $ — Operating loss ​ $ (119) Net loss ​ $ (119) ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 Current assets ​ $ 3,086 Non-current assets ​ 13,103 Total assets ​ $ 16,189 ​ ​ ​ ​ Current liabilities ​ $ 6,770 Non-current liabilities ​ — Total liabilities ​ $ 6,770 ​ bp Joint Venture ​ On April 13, 2021, the Company entered an agreement (“bp JV Agreement”) with bp that created a 50/50 joint venture (“bpJV”) to develop, own and operate new ADG RNG production facilities in the United States. Pursuant to the bp JV Agreement, bp and the Company committed to provide $50.0 million and $30.0 million, respectively, with bp Pursuant to the bp JV Agreement, the Company had the option, exercisable prior to August 31, 2021 (the “bp Option”), to commit an additional $20.0 million to the bpJV upon which bp’s Class B Units would convert into Class A Units. On June 21, 2021, the Company contributed $50.2 million to the bpJV, which consisted of (i) its initial contribution commitment of $30.0 million, (ii) the $20.0 million additional contribution to effect the conversion of bp’s Class B Units into Class A Units pursuant to the Company’s exercise of the bp Option, and (iii) $0.2 million for interest on bp’s Class B Units to acquire additional Class A Units. In December 2021, the bpJV authorized a capital call (the “bpJV Capital Call”) for additional funding of $143.2 million, requiring bp Company The Company accounts for its interest in the bpJV using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over the bpJV’s operations. The Company recorded a loss of $0.4 million from this investment for the year ended December 31, 2021, related to formation expenses. The Company had an investment balance in the bpJV of $69.8 million as of December 31, 2021. Combined summarized financial information for the bpJV is as follows (in thousands): ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 Revenue ​ $ — Gross profit ​ $ — Operating loss ​ $ (678) Net loss ​ $ (603) Net loss attributable to bpJV ​ $ (599) ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 Current assets $ 152,072 Non-current assets ​ ​ 70,433 Total assets ​ $ 222,505 ​ ​ ​ ​ Current liabilities ​ $ 24,932 Non-current liabilities ​ ​ 1,000 Total liabilities ​ $ 25,932 ​ ​ ​ ​ Equity attributable to shareowners of bpJV ​ $ 191,170 Equity attributable to noncontrolling interest ​ ​ 5,403 Total equity ​ $ 196,573 ​ SAFE&CEC S.r.l. ​ On December 29, 2017, the Company obtained a 49% ownership interest in SAFE&CEC S.r.l. See Note 3 for more information. Summarized financial information for SAFE&CEC S.r.l. is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2020 ​ 2021 Revenue ​ $ 80,886 ​ $ 89,535 ​ $ 109,119 Gross profit ​ $ 20,525 ​ $ 19,008 ​ $ 25,784 Operating income ​ $ 1,207 ​ $ 609 ​ $ 4,728 Net income (loss) ​ $ 93 ​ $ (306) ​ $ 2,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ ​ ​ 2020 ​ 2021 Current assets ​ ​ ​ $ 60,406 ​ $ 75,137 Non-current assets ​ ​ ​ ​ ​ 58,140 ​ ​ 56,052 Total assets ​ ​ ​ ​ $ 118,546 ​ $ 131,189 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ ​ ​ ​ $ 55,780 ​ $ 58,910 Non-current liabilities ​ ​ ​ ​ ​ 11,808 ​ ​ 21,730 Total liabilities ​ ​ ​ ​ $ 67,588 ​ $ 80,640 ​ Other Equity Method Investments ​ The Company had an investment balance in other equity method investments of $2.3 million and $3.5 million as of December 31, 2020 and 2021, respectively. The Company recorded income (loss) from other equity method investments of $(0.1) million, $0.1 million, and $(0.6) million for the years ended December 31, 2019, 2020 and 2021, respectively. The Company accounts for its interest using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over the investees’ operations. Combined summarized financial information for the Company’s other equity method investments is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2020 ​ 2021 Revenue ​ $ 546 ​ $ 463 ​ $ 704 Gross profit ​ $ 178 ​ $ 155 ​ $ 216 Operating loss ​ $ (214) ​ $ (90) ​ $ (1,757) Net loss ​ $ (250) ​ $ (126) ​ $ (1,793) ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2020 ​ 2021 Current assets ​ $ 1,233 ​ $ 1,349 Non-current assets ​ 5,553 ​ 7,047 Total assets ​ $ 6,786 ​ $ 8,396 ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ $ 1,421 ​ $ 1,012 Non-current liabilities ​ 66 ​ 192 Total liabilities ​ $ 1,487 ​ $ 1,204 ​ 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. In connection with the arrangement between NG Advantage and bp for the supply, sale and reservation of a specified volume of CNG transportation capacity until February 2022, on February 28, 2018, the Company entered into a guaranty agreement with NG Advantage and bp pursuant to which the Company guarantees NG Advantage’s payment obligations to bp in the event of default by NG Advantage under the supply arrangement, in an amount up to an aggregate of $30.0 million plus related fees which was reduced to $15.0 million effective June 24, 2020. As initial consideration for the guaranty agreement, NG Advantage issued to the Company 19,660 common units, which increased the Company’s controlling interest in NG Advantage from 53.3% to 53.5%. On October 1, 2018, the Company purchased 1,000,001 common units from NG Advantage for an aggregate cash purchase price of $5.0 million. This purchase increased Clean Energy’s controlling interest in NG Advantage from 53.5% to 61.7%. In each month from November 2018 through February 2019, the Company was issued 100,000 additional common units of NG Advantage, for a total of 400,000 common units, pursuant to the guaranty agreement entered in February 2018. The issuance of 400,000 additional common units increased the Company’s controlling interest in NG Advantage to 64.6%. During the year ended December 31, 2019, the Company agreed to lend NG Advantage up to $26.7 million under a series of promissory notes that were incorporated into a delayed draw convertible promissory note (the “November 2019 Convertible Note”). In connection with the promissory notes between NG Advantage and the Company, NG Advantage issued to the Company warrants to purchase 2,086,879 common units. 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 of NG Advantage pursuant to the guaranty agreement entered in February 2018, which increased the Company’s controlling interest in NG Advantage to 93.3% as of December 31, 2020. During the year ended December 31, 2021, NG Advantage borrowed $5.0 million from the Company under a series of advance agreements. As of December 31, 2021, NG advantage had an outstanding balance of $18.4 million, plus accrued and unpaid interest under the advance agreements. This intercompany transaction has been eliminated in consolidation. The Company recorded a loss attributable to the noncontrolling interest in NG Advantage of $7.2 million, $1.7 million, and $1.0 million for the years ended December 31, 2019, 2020 and 2021, respectively. The noncontrolling interest was $9.3 million and $8.3 million as of December 31, 2020 and 2021, respectively. Investments in Equity Securities For investments in equity securities of privately held entities without readily determinable fair values, the Company measures such investments at cost, adjusted for impairment, if any, and observable price changes in orderly transactions for the identical or similar investment of the same issuer. As of December 31, 2021, the Company had investment balance recorded at cost of $8.0 million. The Company did not recognize any adjustments to the recorded cost basis during the year ended December 31, 2021.

Cash, Cash Equivalents, and Res

Cash, Cash Equivalents, and Restricted Cash	12 Months Ended
	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents, and Restricted Cash	Note 5 —Cash, Cash Equivalents and Restricted Cash Cash, cash equivalents and restricted cash as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Current assets: ​ ​ Cash and cash equivalents ​ $ 108,977 ​ $ 99,448 Total cash and cash equivalents ​ $ 108,977 ​ $ 99,448 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ — Restricted cash - held as collateral ​ ​ 7,000 ​ ​ 7,008 Total restricted cash ​ $ 11,000 ​ $ 7,008 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 119,977 ​ $ 106,456 ​ The Company considers all highly liquid investments with maturities of three months or less on the date of acquisition to be cash equivalents. The Company places its cash and cash equivalents with high credit quality financial institutions. At times, such investments may be in excess of the Federal Deposit Insurance Corporation (“FDIC”) and Canadian Deposit Insurance Corporation (“CDIC”) 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 $107.6 million and $98.0 million as of December 31, 2020 and 2021, 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. Long-term restricted cash consisted of cash held as collateral for the benefit of a lender to NG Advantage.

Short-Term Investments

Short-Term Investments	12 Months Ended
	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Short-Term Investments	Note 6 — 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 (loss), 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 December 31, 2021, 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, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gain (Loss) Fair Value Municipal bonds and notes ​ $ 28,998 ​ $ — ​ $ 28,998 Certificates of deposit ​ 530 ​ — ​ 530 Total short-term investments ​ $ 29,528 ​ $ — ​ $ 29,528 ​ Short-term investments as of December 31, 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Loss Fair Value Municipal bonds and notes ​ $ 6,001 ​ $ (1) ​ $ 6,000 Zero coupon bonds ​ ​ 123,210 ​ ​ (18) ​ ​ 123,192 Certificates of deposit ​ ​ 530 ​ ​ — ​ ​ 530 Total short-term investments ​ $ 129,741 ​ $ (19) ​ $ 129,722 ​

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	Note 7 - Derivative Instruments and Hedging Activities In October 2018, the Company executed two commodity swap contracts with TotalEnergies Gas & Power North America, an affiliate of TotalEnergies and THUSA (as defined in Notes 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 recorded at fair value at the time of execution, with the changes in fair value of the embedded derivatives recognized as earnings in "Product revenue" in the accompanying consolidated statements of operations. Derivatives and embedded derivatives as of December 31, 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 ​ $ 1,591 ​ $ — ​ $ 1,591 Long-term portion of derivative assets, related party ​ ​ 4,057 ​ ​ ​ ​ ​ 4,057 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 249 ​ ​ — ​ ​ 249 Notes receivable and other long-term assets, net ​ ​ 542 ​ ​ — ​ ​ 542 Total derivative assets ​ $ 6,439 ​ $ — ​ $ 6,439 Liabilities: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ $ 283 ​ $ — ​ $ 283 Other long-term liabilities ​ ​ 273 ​ ​ — ​ ​ 273 Total derivative liabilities ​ $ 556 ​ $ — ​ $ 556 ​ Derivatives and embedded derivatives as of December 31, 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ $ 2,038 ​ $ — ​ $ 2,038 Notes receivable and other long-term assets, net ​ ​ 4,738 ​ ​ — ​ ​ 4,738 Total derivative assets ​ $ 6,776 ​ $ — ​ $ 6,776 Liabilities: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative liabilities, related party ​ $ 1,900 ​ $ — ​ $ 1,900 Long-term portion of derivative liabilities, related party ​ ​ 2,483 ​ ​ ​ ​ ​ 2,483 Total derivative liabilities ​ $ 4,383 ​ $ — ​ $ 4,383 ​ As of December 31, 2020 and 2021, the Company had a total volume on open commodity swap contracts of 16.9 million and 11.9 million diesel gallons, respectively, at a weighted-average price per gallon of approximately $3.18 per gallon. The following table reflects the weighted-average price of open commodity swap contracts as of December 31, 2020 and 2021, by year with associated volumes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 ​ ​ Volumes ​ Weighted-Average Price per ​ Volumes ​ Weighted-Average Price per Year (Diesel Gallons) Diesel Gallon (Diesel Gallons) Diesel Gallon 2021 ​ 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	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 8 —Fair Value Measurements The Company follows the authoritative guidance for fair value measurements with respect to assets and liabilities that are measured at fair value on a recurring basis and non-recurring basis. Under the standard, fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as of the measurement date. The standard also establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs market participants would use in valuing the asset or liability developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the factors market participants would use in valuing the asset or liability developed based upon the best information available in the circumstances. The hierarchy consists of the following three levels: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and inputs (other than quoted prices) that are observable for the asset or liability, either directly or indirectly; Level 3 inputs are unobservable inputs for the asset or liability. Categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Assets and Liabilities Measured at Fair Value on a Recurring Basis The Company’s available-for-sale debt securities and certificate of deposits are classified within Level 2 because they are valued using the most recent quoted prices for identical assets in markets that are not active and quoted prices for similar assets in active markets. The Company used the income approach to value its outstanding commodity swap contracts 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, 2020 and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13 ​ The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13 ​ 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, 2020 or 2021. 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, 2020 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 28,998 ​ $ — ​ $ 28,998 ​ $ — Certificates of deposit (1) ​ 530 ​ — ​ 530 ​ — Commodity swap contracts (2) ​ ​ 5,648 ​ — ​ — ​ 5,648 Embedded derivatives (3) ​ ​ 791 ​ ​ — ​ ​ — ​ ​ 791 Liabilities: ​ ​ ​ ​ ​ Embedded derivatives (3) ​ $ 556 ​ $ — ​ $ — ​ $ 556 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 Level 1 Level 2 Level 3 Assets: ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 6,000 ​ $ — ​ $ 6,000 ​ $ — Zero coupon bonds ​ 123,192 ​ — ​ 123,192 ​ — Certificates of deposit (1) ​ ​ 530 ​ ​ — ​ ​ 530 ​ ​ — Embedded derivatives (3) ​ ​ 6,776 ​ ​ — ​ ​ — ​ ​ 6,776 Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ Commodity swap contracts (2) ​ $ 4,383 ​ $ — ​ $ — ​ $ 4,383 (1) Included in “Short-term investments” in the accompanying consolidated balance sheets. See Note 6 for more information. (2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” as of December 31, 2020, and “Derivative liabilities, related party” and “Long-term portion of derivative liabilities, related party” as of December 31, 2021, in the accompanying consolidated balance sheets. See Note 7 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” as of December 31, 2020, and "Prepaid expenses and other current assets" and "Notes receivable and other long-term assets, net" as of December 31, 2021 in the accompanying consolidated balance sheets. See Note 7 for more information. ​ The following table provides a reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis as shown in the tables above that used significant unobservable inputs (Level 3), 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 December 31, 2019 ​ $ 3,270 ​ $ 723 ​ $ (164) ​ $ (81) ​ $ (40) Settlements, net ​ ​ (1,652) ​ ​ — ​ ​ 56 ​ ​ — ​ ​ — Total gain (loss) ​ 4,030 ​ ​ 68 ​ ​ 108 ​ ​ (475) ​ ​ 40 Balance as of December 31, 2020 ​ $ 5,648 ​ $ 791 ​ $ — ​ $ (556) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of December 31, 2020 ​ $ 5,648 ​ $ 791 ​ $ — ​ $ (556) ​ $ — Settlements, net ​ ​ (225) ​ ​ — ​ ​ 1,083 ​ ​ — ​ ​ — Total gain (loss) ​ (5,423) ​ ​ 5,985 ​ ​ (5,466) ​ ​ 556 ​ ​ — Balance as of December 31, 2021 ​ $ — ​ $ 6,776 ​ $ (4,383) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the year ended December 31, 2020 included in earnings ​ $ 2,378 ​ $ 68 ​ $ 164 ​ $ (475) ​ $ 40 Change in unrealized gain (loss) for the year ended December 31, 2021 included in earnings ​ $ (5,648) ​ $ 5,985 ​ $ (4,383) ​ $ 556 ​ $ — ​ 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, 2020 and 2021. The fair values of these debt instruments were estimated using a discounted cash flow analysis based on interest rates offered on loans with similar terms to borrowers of similar credit quality, which are Level 3 inputs. See Note 12 for more information about the Company’s debt instruments.

Other Receivables

Other Receivables	12 Months Ended
	Dec. 31, 2021
Receivables [Abstract]
Other Receivables	Note 9 —Other Receivables Other receivables as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Loans to customers to finance vehicle purchases ​ $ 394 ​ $ 419 Accrued customer billings ​ 6,335 ​ 4,417 Fuel tax credits ​ 10,556 ​ 12,684 Other ​ 6,370 ​ 6,927 Total other receivables ​ $ 23,655 ​ $ 24,447 ​

Land, Property and Equipment

Land, Property and Equipment	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Land, Property and Equipment	Note 10 —Land, Property and Equipment Land, property and equipment, net as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Land ​ $ 3,476 ​ $ 3,476 LNG liquefaction plants ​ 94,633 ​ 94,633 Station equipment ​ 344,839 ​ 354,699 Trailers ​ 79,860 ​ 72,783 Other equipment ​ 89,276 ​ 93,135 Construction in progress ​ 73,272 ​ 74,963 ​ ​ 685,356 ​ 693,689 Less accumulated depreciation ​ (394,445) ​ (431,928) Total land, property and equipment, net ​ $ 290,911 ​ $ 261,761 ​ Included in "Land, property and equipment, net" are capitalized software costs of $32.3 million and $33.8 million as of December 31, 2020 and 2021, respectively. Accumulated amortization of the capitalized software costs are $28.8 million and $30.4 million as of December 31, 2020 and 2021, respectively. The Company recorded amortization expense related to the capitalized software costs of $3.9 million, $2.5 million and $1.6 million for the years ended December 31, 2019, 2020 and 2021, respectively. As of December 31, 2020 and 2021, $1.7 million and $2.1 million, respectively, are included in "Accounts payable" and "Accrued liabilities" in the accompanying consolidated balance sheets, representing amounts related to purchases of property and equipment. These amounts are excluded from the accompanying consolidated statements of cash flows as they are non-cash investing activities.

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued Liabilities	Note 11 —Accrued Liabilities Accrued liabilities as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Accrued alternative fuels incentives (1) ​ $ 18,175 ​ $ 28,106 Accrued employee benefits ​ 4,282 ​ 4,547 Accrued gas and equipment purchases ​ 9,897 ​ 17,158 Accrued interest ​ 512 ​ 893 Accrued property and other taxes ​ 3,094 ​ 3,369 Accrued salaries and wages ​ 7,646 ​ 8,172 Embedded derivatives ​ ​ 283 ​ ​ — Other (2) ​ 8,748 ​ 12,914 Total accrued liabilities ​ $ 52,637 ​ $ 75,159 (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	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt	Note 12 —Debt Debt obligations as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs bp Loan ​ $ 50,000 $ — ​ $ 50,000 NG Advantage debt ​ 29,535 ​ 117 ​ 29,418 SG Facility ​ ​ 5,100 ​ ​ — ​ ​ 5,100 Other debt ​ 1,162 ​ — ​ 1,162 Total debt ​ 85,797 ​ 117 ​ 85,680 Less amounts due within one year ​ (3,631) ​ (39) ​ (3,592) Total long-term debt ​ $ 82,166 ​ $ 78 ​ $ 82,088 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs NG Advantage debt ​ $ 25,832 ​ ​ 72 ​ ​ 25,760 SG Facility ​ ​ 9,500 ​ ​ — ​ ​ 9,500 Other debt ​ 800 ​ ​ — ​ ​ 800 Total debt ​ 36,132 ​ 72 ​ 36,060 Less amounts due within one year ​ (12,868) ​ ​ (23) ​ ​ (12,845) Total long-term debt ​ $ 23,264 ​ $ 49 ​ $ 23,215 ​ The following is a summary of the aggregate maturities of debt obligations for each of the annual periods subsequent to December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2022 2023 2024 2025 2026 Thereafter ​ Total NG Advantage debt ​ $ 2,991 ​ $ 8,977 ​ $ 4,161 ​ $ 1,397 ​ $ 8,306 ​ $ — ​ $ 25,832 SG Facility ​ ​ 9,500 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 9,500 Other Debt ​ ​ 377 ​ ​ 262 ​ ​ 161 ​ ​ — ​ ​ — ​ ​ — ​ ​ 800 Total ​ $ 12,868 ​ $ 9,239 ​ $ 4,322 ​ $ 1,397 ​ $ 8,306 ​ $ — ​ $ 36,132 ​ 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 The Company is required to make quarterly principal payments of $2.5 million beginning March 31, 2022 with any unpaid amount due on January 2, 2024, subject to the option to extend the maturity date for three successive terms of one year each. The Company is required to make mandatory prepayments under the SG Facility equal to any amounts the Company receives for complete or partial refunds of the incremental cost of trucks purchased or financed under the 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 December 31, 2021, the Company had $9.5 million outstanding on the SG Facility and no events of defaults had occurred. TotalEnergies Credit Support Agreement The Company entered into a credit support agreement with TotalEnergies Holdings USA Inc. (“THUSA”), a wholly owned subsidiary of TotalEnergies, on January 2, 2019, which was subsequently amended on March 12, 2021 (as amended, the “CSA”) in conjunction with the March 12, 2021 amendment to the Credit Agreement. Under the CSA, THUSA agreed to enter into a guaranty agreement (“Guaranty”) pursuant to which it has guaranteed the Company’s obligation to repay 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 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 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 is payable monthly in 72 equal monthly installments at an annual rate of 5.17%. As collateral security for the prompt payment in full when due of NG Advantage’s obligations to Wintrust under the Wintrust LSA, NG Advantage pledged to and granted Wintrust a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received under the Wintrust LSA. On December 10, 2020, NG Advantage entered an Amended and Restated Loan and Security Agreement with Berkshire Bank (“Berkshire ALA”) to substitute and replace the two existing loans with Berkshire Bank dated May 12, 2016 and January 24, 2017 (collectively, the “Original Debt”). The Berkshire ALA provides NGA a 5-year term loan of $14.5 million with payments of principal and interest due monthly beginning February 1, 2021 at an annual interest rate of 5% maturing on January 1, 2026. NG Advantage used the funds provided by the Berkshire ALA to repay in full the outstanding principal balance plus accrued and unpaid interest of the Original Debt, and to repay the outstanding balances of certain other financing obligations to unrelated lenders, Nations and Liberty. NG Advantage has pledged as collateral certain assets and equipment including trailers under the Berkshire ALA, and the Company has provided a limited guaranty of up to $7.0 million classified in “Restricted cash” on the accompanying consolidated balance sheet. As of December 31, 2021, the Company was in compliance with the covenants under the Berkshire ALA. ​ The Berkshire ALA also provides NG Advantage a $1.0 million revolving line of credit which bears interest at the greater of the Prime Rate or 3.00%, plus 0.25% and has a maturity date of July 31, 2022. As of December 31, 2021, NG Advantage had no amounts outstanding on the revolving line of credit. ​ 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 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 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%. bp Loan On December 18, 2020, the Company entered a memorandum of understanding (“MOU”) with bp to create the bpJV. Contemporaneous with the execution of the MOU, the Company and bp executed a loan agreement whereby bp advanced $50.0 million (“bp Loan”) to fund capital costs and expenses incurred prior to formation of the bpJV. The bp Loan bore interest at the rate per annum equal to LIBOR plus 4.33% . As repayment of the bp Loan, the outstanding principal balance was contributed to the bpJV in April 2021 upon entering into the bp JV Agreement. See Note 4 for additional information. Plains Credit Facility On May 1, 2021, the Company entered into a Loan and Security Agreement (the “Plains LSA”) with PlainsCapital Bank (“Plains”), which provides the Company a $20.0 million revolving line of credit through May 1, 2022. The interest rate on amounts outstanding under the Plains LSA is the greater of the Prime Rate or 3.25%. As of December 31, 2021, no amounts were outstanding under the Plains LSA. As of December 31, 2021, the Company was in compliance with the covenants under the Plains LSA. On September 16, 2021, Plains issued an irrevocable standby letter of credit on behalf of the Company to the Chevron Products Company, a division of Chevron U.S.A. Inc. (“Chevron”), for $2.0 million relating to the Company’s Adopt-A-Port program with Chevron. The standby letter of credit is valid until cancelled and is collateralized by the Company’s revolving line of credit with Plains, reducing the amount available under the line of credit from $20.0 million to $18.0 million. As of December 31, 2021, no amounts have been drawn under the standby letter of credit. Other Debt The Company has other debt due at various dates through 2024 bearing interest at rates up to 4.75%with a weighted-average interest rate of 4.38% and 4.34% as of December 31, 2020 and 2021, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Note 13 —Stockholders’ Equity Authorized Shares The Company’s certificate of incorporation authorizes the issuance of two classes of capital stock designated as common stock and preferred stock stockholders approved an increase in the number of shares of Common Stock the Company is authorized to issue from 304,000,000 to 454,000,000. As of December 31, 2021, the Company is authorized to issue 455,000,000 shares, of which 454,000,000 shares of capital stock are designated common stock and 1,000,000 shares are designated preferred stock. Dividend Provisions The Company did not declare or pay any dividends during the years ended December 31, 2019, 2020 and 2021. Voting Rights Each holder of common stock has the right to one vote per share owned on matters presented for stockholder action. TotalEnergies Private Placement On May 9, 2018, the Company entered into a stock purchase agreement (the “Purchase Agreement”) with TotalEnergies Marketing Services, S.E. (“TMS”), a wholly owned subsidiary of TotalEnergies. Pursuant to the Purchase Agreement, the Company agreed to sell and issue, and TMS agreed to purchase, up to 50,856,296 shares of the Company’s common stock at a purchase price of $1.64 per share, all in a private placement (the “TotalEnergies Private Placement”). The purchase price per share was determined based on the volume-weighted average price for the Company’s common stock between March 23, 2018 (the day on which discussions began between the Company and TotalEnergies) and May 3, 2018 (the day on which the Company agreed in principle with TotalEnergies regarding the structure and basic terms of its investment). As of the date of the Purchase Agreement, TotalEnergies did not hold or otherwise beneficially own any shares of the Company’s common stock, and TotalEnergies has agreed, until the later of May 9, 2020 or such date when it ceases to hold more than 5.0% of the Company’s common stock then outstanding, among other similar undertakings and subject to customary conditions and exceptions, to not purchase shares of the Company’s common stock or otherwise pursue transactions that would result in TotalEnergies beneficially owning more than 30.0% of the Company’s equity securities without the approval of the Company’s board of directors. On June 13, 2018, the Company and TMS closed the TotalEnergies Private Placement, in which: (1) the Company issued to TMS all of the 50,856,296 shares of its common stock issuable under the Purchase Agreement, resulting in TotalEnergies beneficially holding approximately 25.0% of the outstanding shares of the Company’s common stock and the largest ownership position of the Company as of September 30, 2018; (2) TotalEnergies paid to the Company an aggregate of $83.4 million in gross proceeds, which the Company has used and expects to continue to use for working capital and general corporate purposes, which may include executing its business plans, pursuing opportunities for further growth, and retiring a portion of its outstanding indebtedness; and (3) the Company and TotalEnergies entered into a registration rights agreement, described below. In connection with the issuance of common stock, the Company incurred transaction fees of $1.9 million. Pursuant to the Purchase Agreement, the Company and TotalEnergies also entered into a registration rights agreement on June 13, 2018, upon the closing under the Purchase Agreement. Pursuant to the registration rights agreement, the Company filed a registration statement with the SEC to cover the resale of the shares issued and sold under the Purchase Agreement, which was declared effective on August 16, 2018, and is obligated to use its commercially reasonable efforts to maintain the effectiveness of such registration statement until all such shares are sold or may be sold without restriction under Rule 144 under the Securities Act of 1933, as amended. As of December 31, 2021, the Company was in compliance with all of its registration covenants set forth in the registration rights agreement. At-The-Market Offerings On May 10, 2021, the Company entered into an equity distribution agreement with Goldman Sachs & Co. LLC, as sales agent, to sell shares of the Company’s common stock having an aggregate offering price of up to $100.0 million in an at-the-market offering program (the “May ATM Program”). Through June 3, 2021, the Company sold 12,362,237 shares of common stock under the May ATM Program, which exhausted the May ATM Program. On June 7, 2021, the Company entered into a new equity distribution agreement with Goldman Sachs & Co. LLC, as sales agent, to sell additional shares of common stock having an aggregate offering price of up to $100.0 million in a new at-the-market offering program (the “June ATM Program” and, together with the May ATM Program, the “ATM Programs”). On June 8, 2021, the Company sold 10,473,946 shares of common stock under the June ATM Program which exhausted the June ATM Program. For the year ended December 31, 2021, the Company issued 22,836,183 shares of common stock under the ATM Programs for gross proceeds of $200.0 million, and incurred transaction costs of $6.5 million, including $6.0 million in commissions paid to Goldman Sachs & Co. LLC. 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”). On December 7, 2021, the Company’s Board of Directors approved an increase in the aggregate purchase amount under the Repurchase Program from $30.0 million to $50.0 million (exclusive of fees and commissions). The Repurchase Program does not have an expiration date, and it may be suspended or discontinued at any time. During the year ended December 31, 2021, the Company repurchased 452,700 shares of its common stock under the Repurchase Program for a total cost of $2.9 million. As of December 31, 2021, the Company had utilized a total of $17.4 million under the Repurchase Program to repurchase 8,197,086 shares of common stock. 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. 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 consolidated statements of operations during the periods presented (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2019 2020 2021 Stock-based compensation expense, net of $0 tax in 2019, 2020, and 2021 ​ $ 3,880 ​ $ 2,957 ​ $ 14,994 ​ Equity Incentive Plans In December 2006, the Company adopted its 2006 Equity Incentive Plan (“2006 Plan”), which became effective on May 24, 2007, the date the Company completed its initial public offering of common stock. In May 2016, the Company adopted its 2016 Performance Incentive Plan (“2016 Plan”), which became effective on May 26, 2016, the date of approval of the 2016 Plan by the Company’s stockholders. The 2006 Plan became unavailable for new awards upon the effectiveness of the 2016 Plan. Unissued awards under the 2006 Plan are not available for future grant under the 2016 Plan. If any outstanding award under the 2006 Plan expires or is canceled, the shares allocable to the unexercised portion of that award will be added to the share reserve under the 2016 Plan and will be available for grant under the 2016 Plan. 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 15, 2020, the date of approval of the Amended 2016 Plan by the Company’s stockholders. As of December 31, 2021, the Company had 7,595,607 shares available for future grant under the Amended 2016 Plan. Service-Based Stock Options The Company has granted service-based stock options to key employees that vest annually over the three years following the date of grant at a rate of 34%, 33% and 33%, respectively, if the holder is in service to the Company at each vesting date. The service-based stock options granted have contractual terms of 10 years, and exercise price for the options granted is equal to the closing market price of the Company's common stock on the date of grant. The stock options are subject to the terms and conditions of the 2006 and 2016 Plans and a Notice of Grant of Stock Option and Stock Option Agreement. The following table summarizes the Company’s service-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 8,142,831 ​ $ 5.38 ​ Granted 6,186,260 ​ 8.32 ​ ​ ​ ​ ​ Exercised (1,219,976) ​ 4.59 ​ ​ ​ ​ ​ Forfeited or expired (1,295,444) ​ 8.68 ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 11,813,671 ​ $ 6.64 ​ 7.27 ​ $ 15,409 Options exercisable as of December 31, 2021 5,133,792 ​ $ 5.52 ​ 4.37 ​ $ 12,329 Options vested and expected to vest as of December 31, 2021 11,813,671 ​ $ 6.64 ​ 7.27 ​ $ 15,409 ​ As of December 31, 2021, there was $25.9 million of total unrecognized compensation cost related to unvested shares subject to outstanding service-based stock options. That cost is expected to be expensed over a remaining weighted average period of approximately 2.3 years. The total fair value of shares vested during the year ended December 31, 2021 was $1.8 million. The fair value of each service-based stock option granted was estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2019 2020 2021 Dividend yield 0.0% ​ 0.0% ​ 0.0% Expected volatility 57.3% to 61.5% ​ 65.8% to 83.9% ​ 76.8% to 96.8% Risk-free interest rate 2.11% to 2.53% ​ 0.37% to 1.21% ​ 0.58% to 1.31% Expected life in years 6.0 6.0 5.6 to 5.8 ​ The volatility amounts used were estimated based on (i) the historical volatility of the Company’s common stock over a term equal to the estimated life of the options and on (ii) implied volatility of the Company’s traded options. The expected lives used were based on historical exercise experience and the Company’s anticipated exercise periods for its outstanding stock options. The risk-free interest rates used were based on the U.S. Treasury yield curve with terms approximating the expected life of the stock options at the time of grant. The weighted-average grant date fair value per share of service-based stock options granted during the years ended December 31, 2019, 2020 and 2021, were $1.28, $1.54 and $5.90, respectively. The aggregate intrinsic value of service- based options exercised during the years ended December 31, 2019, 2020 and 2021 was $0.1 million, $1.8 million and $10.1 million, respectively. The Company recorded $2.2 million, $1.7 million and $9.9 million of stock option expense relating to service-based stock options during the years ended December 31, 2019, 2020 and 2021, respectively. The Company has not recorded any tax benefit related to its service-based stock option expense. Performance-Based Stock Options The Company has granted 1,640,000 performance-based stock options to certain executives and key employees during 2021. The options granted vest in multiple tranches in which vesting of each tranche is contingent upon securing a defined RNG production volume following the date of grant, if the holder is in service to the Company upon the achievement of such performance hurdles. The performance-based stock options have contractual terms of 10 years, and the exercise price for the options granted is equal to the closing market price of the Company's common stock on the date of grant. The stock options are subject to the terms and conditions of the 2016 Plan and a Notice of Grant of Stock Option and Stock Option Agreement. The following table summarizes the Company’s performance-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 — ​ ​ ​ ​ ​ Granted 1,640,000 ​ 6.77 ​ ​ ​ ​ ​ Exercised — ​ ​ ​ ​ ​ ​ ​ Forfeited or expired — ​ ​ ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 1,640,000 ​ $ 6.77 ​ 9.94 ​ $ — Options exercisable as of December 31, 2021 — ​ $ — ​ — ​ $ — ​ As of December 31, 2021, there was $6.6 million of total unrecognized compensation cost related to unvested shares subject to outstanding performance-based stock options. Compensation cost for the performance-based stock options is recognized when attainment of the performance hurdles is determined to be probable and over a period in which the Company estimates the performance hurdles will be achieved. No vesting occurred during the year ended December 31, 2021. The fair value of each performance-based stock option granted was estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions: ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 Dividend yield ​ 0.0% Expected volatility ​ 77.1% Risk-free interest rate ​ 1.36% Expected life in years 6.2 ​ The volatility amount used was estimated based on (i) the historical volatility of the Company’s common stock over a term equal to the estimated life of the options and on (ii) implied volatility of the Company’s traded options. The expected life used was based on historical exercise experience and the Company’s anticipated exercise period for its outstanding performance-based stock options. The risk-free interest rate used was based on the U.S. Treasury yield curve with terms approximating the expected life of the stock options at the time of grant. The weighted-average grant date fair value per share of performance-based stock options granted during the year ended December 31, 2021, was $4.58. There were no performance-based stock options exercised during the year ended December 31, 2021. The Company recognizes the grant date fair value of the options that are probable of being earned over the estimated performance period. Compensation cost on performance-based stock options was $1.0 million for the year ended December 31, 2021. The Company has not recorded any tax benefit related to its performance-based stock option expense. Market-Based Stock Options The Company has granted 3,700,000 market-based stock options to select executives and employees during 2021. Market-based stock options vest if (i) the closing price of the Company’s common stock equals or exceeds $14.00 for twenty The following table summarizes the Company’s market-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 — ​ ​ ​ ​ ​ Granted 3,700,000 ​ 6.77 ​ ​ ​ ​ ​ Exercised — ​ ​ ​ ​ ​ ​ ​ Forfeited or expired — ​ ​ ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 3,700,000 ​ $ 6.77 ​ 9.94 ​ $ — Options exercisable as of December 31, 2021 — ​ $ — ​ — ​ $ — ​ As of December 31, 2021, there was $17.8 million of total unrecognized compensation cost related to unvested shares subject to outstanding market-based stock options. That cost is expected to be expensed over a remaining weighted average period of approximately 6.8 years. No vesting occurred during the year ended December 31, 2021. The fair value of each market-based stock option granted was estimated on the date of grant using the Monte Carlo simulation model. The Monte Carlo simulation method is subject to variability as certain assumptions must be made, including the derived service period, which is estimated based on likely future stock price performance and volatility of the Company’s common stock price. The fair value of each market-based stock option granted was estimated using the following assumptions: ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 Dividend yield ​ 0.0% Expected volatility ​ 67.8% Risk-free interest rate ​ 1.5% Expected life in years 10.0 ​ The volatility amount used was based on the historical volatility of the Company’s common stock over a term equal to the estimated life of the options. The risk-free interest rate used was based on the U.S. Treasury yield curve with terms approximating the expected life of the stock options at the time of grant. The expected life used was based on the Company’s anticipated exercise period for its outstanding market-based stock options as the simulation was run from the valuation date through the end of the contractual life of the options using weekly time steps. The weighted-average grant date fair value per share of market-based stock options granted during the year ended December 31, 2021, was $4.87. There were no market-based stock options exercised during the year ended December 31, 2021. The Company recorded $0.2 million of compensation cost relating to market-based stock options during the year ended December 31, 2021. The Company has not recorded any tax benefit related to its market-based stock option expense. Service-Based Restricted Stock Units The Company has granted service-based restricted stock units (“Service-Based RSUs”) to key employees that vest annually over the three years following the date of grant at a rate of 34%, 33% and 33%, respectively, if the holder is in service to the Company at each vesting date. The Service-Based RSUs are subject to the terms and conditions of the 2016 Plan and a Notice of Grant of Restricted Stock Unit and Restricted Stock Unit Agreement. The following table summarizes the Company’s Service-Based RSU activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ Number of ​ Fair Value at ​ Shares Grant Date RSU outstanding and unvested as of December 31, 2020 978,716 ​ $ 1.71 Granted 894,344 ​ 10.24 Vested (722,193) ​ 2.54 Forfeited or expired (23,925) ​ 6.86 RSU outstanding and unvested as of December 31, 2021 1,126,942 ​ $ 8.08 ​ The weighted average grant-date fair value of RSUs granted during the years ended December 31, 2020 and 2021 was $2.56 and $10.24, respectively. As of December 31, 2021, there was $6.2 million of total unrecognized compensation cost related to unvested shares subject to outstanding Service-Based RSUs. That cost is expected to be expensed over a remaining weighted-average period of approximately 1.8 years. The Company recorded $1.5 million, $1.0 million and $3.9 million of expense during the years ended December 31, 2019, 2020 and 2021, respectively, related to the Service-Based RSUs. The Company has not recorded any tax benefit related to its Service-Based RSU expense. Employee Stock Purchase Plan On May 7, 2013, the Company adopted an employee stock purchase plan (the “ESPP”), pursuant to which eligible employees may purchase shares of the Company’s common stock at 85% of the fair market value of the common stock on the last trading day of two consecutive, non-concurrent offering periods each year. The Company has reserved 2,500,000 shares of its common stock for issuance under the ESPP, and the first offering period under the ESPP commenced on September 1, 2013. The Company recorded $0.0 million of expense during the years ended December 31, 2019 and 2020 and $0.1 million of expense during the year ended December 31, 2021 related to the ESPP. The Company has not recorded any tax benefit related to its ESPP expense. As of December 31, 2021, the Company had issued an aggregate of 669,915 shares pursuant to the ESPP. Amazon Warrant On April 16, 2021, the Company entered into a Project Addendum to Fuel Pricing Agreement (“Fuel Agreement”) with Amazon Logistics, Inc., a subsidiary of Amazon.com, Inc. (“Amazon”), and a Transaction Agreement with Amazon (the “Transaction Agreement”), pursuant to which, among other things, the Company issued to Amazon.com NV Investment Holdings LLC, a subsidiary of Amazon (“Amazon Holdings”), a warrant to purchase up to an aggregate of 53,141,755 shares (the “Warrant Shares”) of the Company’s common stock at an exercise price of $13.49 per share, which was a 21.3% premium to the $11.12 closing price of the common stock on April 15, 2021. The Warrant Shares vest in multiple tranches, the first of which for 13,283,445 Warrant Shares vested upon execution of the Fuel Agreement. Subsequent tranches will vest over time based on fuel purchases by Amazon and its affiliates, up to a total of $500.0 million, excluding any payments attributable to “Pass Through Costs,” which consist of all costs associated with the delivered cost of gas and applicable taxes determined by reference to the selling price of gallons or gas sold. Under the Transaction Agreement, the Company was required to use commercially reasonable efforts to obtain the approval of its stockholders with respect to the issuance of Warrant Shares in excess of 50,595,531 shares of common stock, pursuant to The Nasdaq Stock Market LLC’s Listing Rule 5635(b) (the “Stockholder Approval”). On June 14, 2021, the Company obtained Stockholder Approval. As a result of the issuance of additional shares of common stock under the ATM Programs and in accordance with the terms of the warrant, on June 14, 2021, the number of shares of the Company’s common stock that may be purchased pursuant to the warrant, at an exercise price of $13.49 per share, increased by an aggregate of 5,625,959 shares (the “Additional Warrant Shares”). The Additional Warrant Shares vest in multiple tranches, the first of which for 1,406,490 Additional Warrant Shares vested on June 14, 2021. Subsequent tranches of the Additional Warrant Shares will vest over time based on fuel purchases by Amazon and its affiliates, consistent with the vesting schedule for the Warrant Shares as described above. The right to exercise the warrants and receive the Warrant Shares and Additional Warrant Shares (the “Amazon Warrant”) that have vested expires April 16, 2031. Amazon Holdings may not exercise the Amazon Warrant to the extent such exercise would cause Amazon Holdings to beneficially own more than 4.999% of the number of shares of Common Stock outstanding immediately after giving effect to such exercise (excluding any unvested portion of the Amazon Warrant) (the “Beneficial Ownership Limitation”). Amazon Holdings may, however, waive or modify the Beneficial Ownership Limitation by providing written notice to the Company sixty-one to the Company to the extent the Company is subject to certain acquisition transactions pursuant to a tender or exchange offer). Non-cash stock-based sales incentive contra-revenue charges (“Amazon Warrant Charges”) associated with the Amazon Warrant are recognized as the customer purchases fuel and vesting conditions become probable of being achieved, based on the grant date fair value of the Amazon Warrant. The fair values of the Amazon Warrant were determined as of the grant date in accordance with ASC 718, Compensation – Stock Compensation ​ ​ ​ ​ ​ ​ April 16, 2021 June 14, 2021 Dividend yield 0.0% ​ 0.0% Expected volatility 66.46% ​ 67.97 Risk-free interest rate 1.59% ​ 1.49% Expected term in years 10.0 9.8 ​ The volatility amounts used were estimated based on the historical volatility of the Company’s common stock over a period matching the assumed term of the Amazon Warrant. The expected terms used were based on the term of the Amazon Warrant at the date of issuance. The risk-free interest rates used were based on the U.S. Treasury yield curve for the expected term of the Amazon Warrant at the date of issuance. The following table summarizes the Amazon Warrant activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ Warrant ​ Shares Outstanding and unvested as of December 31, 2020 — Granted 58,767,714 Vested (14,689,935) Outstanding and unvested as of December 31, 2021 44,077,779 ​ As a result of the immediate vesting of a portion of the Warrant Shares and Additional Warrant Shares, the Company recognized Amazon Warrant Charges, in the second quarter of 2021, of $76.6 million and a customer incentive asset of $38.4 million representing Amazon Warrant Charges associated with future contractually required minimum fuel purchases which will be recognized as the fuel is purchased. During the year ended December 31, 2021, Amazon Warrant Charges in the consolidated statements of operations were $83.6 million. Amazon Warrant Charges during the year ended December 31, 2021 included $76.6 million from the immediate vesting of a portion of the Warrant Shares and Additional Warrant Shares and $7.0 million associated with fuel purchases. As of December 31, 2021, the Company had a customer incentive asset of $12.4 million and $22.1 million, classified in “Prepaid expenses and other current assets” and “Notes receivable and other long-term assets, net,” respectively, in the accompanying consolidated balance sheets.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Note 14 —Income Taxes The components of income (loss) before income taxes for the years ended December 31, 2019, 2020 and 2021 are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 U.S. ​ $ 14,981 ​ $ (11,216) ​ $ (93,117) Foreign ​ (864) ​ (4) ​ (919) Total income (loss) before income taxes ​ $ 14,117 ​ $ (11,220) ​ $ (94,036) ​ The provision for income taxes for the years ended December 31, 2019, 2020 and 2021 consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Current: ​ ​ ​ State ​ $ 116 ​ $ 80 ​ $ 54 Foreign ​ 4 ​ 109 ​ (4) Total current ​ 120 ​ 189 ​ 50 Deferred: ​ ​ ​ Federal ​ 293 ​ 48 ​ 18 State ​ 445 ​ 72 ​ 51 Total deferred ​ 738 ​ 120 ​ 69 Total expense ​ $ 858 ​ $ 309 ​ $ 119 ​ Income tax expense (benefit) for the years ended December 31, 2019, 2020 and 2021 computed using the federal income tax rate of 21% as of December 31, 2019, 2020 and 2021 consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Computed expected tax (benefit) ​ $ 2,964 ​ $ (2,356) ​ $ (19,747) Nondeductible expenses ​ 3,087 ​ 2,775 ​ 617 Tax rate differential on foreign earnings ​ 245 ​ (144) ​ 189 Joint ventures ​ 3,745 ​ (5,059) ​ (2) Amazon warrants ​ — ​ ​ — ​ ​ 3,707 Tax credits ​ (10,314) ​ (4,037) ​ (5,299) Other ​ 665 ​ 1,559 ​ 1,463 Change in valuation allowance ​ 466 ​ 7,571 ​ 19,191 Total tax expense ​ $ 858 ​ $ 309 ​ $ 119 ​ On December 20, 2019, AFTC was retroactively extended beginning January 1, 2018 through December 31, 2020. As a result, all AFTC revenue for vehicle fuel the Company sold in the 2018 and 2019 calendar year was recognized during the year ended December 31, 2019. AFTC revenues for vehicle fuel the Company sold in the 2020 and 2021 calendar year were recognized during the year ended December 31, 2020 and 2021, respectively. AFTC for vehicle fuel sales expired on December 31, 2021, and it is not known whether or when AFTC will be reinstated for vehicle fuel sales made after December 31, 2021. The Company recorded a federal tax benefit of $10.5 million, $4.2 million and $4.9 million related to the exclusion of AFTC associated with 2019, 2020 and 2021 fuel sales in excess of its fuel tax obligation, respectively. These amounts increased the Company’s deferred tax asset and the Company’s deferred tax asset valuation allowance. Deferred tax assets and liabilities result from differences between the financial statement carrying amounts and the tax bases of existing assets and liabilities. The tax effect of temporary differences that give rise to deferred tax assets and liabilities as of December 31, 2020 and 2021 are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Deferred tax assets: ​ ​ Accrued expenses ​ $ 4,940 ​ $ 5,379 Lease obligations ​ ​ 6,938 ​ ​ 11,388 Alternative minimum tax and general business credits ​ 6,233 ​ 6,787 Stock option expense ​ 6,648 ​ 7,214 Amazon warrants ​ ​ — ​ ​ 16,026 Other ​ 1,545 ​ 3,167 Depreciation and amortization ​ ​ 1,635 ​ ​ 2,582 Loss carryforwards ​ 119,708 ​ 128,514 Total deferred tax assets ​ 147,647 ​ 181,057 Less valuation allowance ​ (134,974) ​ (162,018) Net deferred tax assets ​ 12,673 ​ 19,039 Deferred tax liabilities: ​ ​ Right-of-use assets ​ ​ (6,788) ​ ​ (11,266) Commodity swap contracts ​ (1,596) ​ (649) Goodwill ​ (2,221) ​ (2,534) Investments in joint ventures and partnerships ​ (2,926) ​ (5,517) Total deferred tax liabilities ​ (13,531) ​ (19,966) Net deferred tax liabilities ​ $ (858) ​ $ (927) ​ As of December 31, 2021, the Company had federal, state and foreign net operating loss carryforwards of approximately $500.1 million, $370.9 million and $2.7 million, respectively. The Company’s federal, state and foreign net operating loss carryforwards will, if not utilized, expire beginning in 2026, 2022 and 2030, respectively. The Company also has federal tax credit carryforwards of $6.8 million that will expire beginning in 2026. Due to the change of ownership provisions of Internal Revenue Code Section 382, utilization of a portion of the Company’s net operating loss and tax credit carryforwards may be limited in future periods. In assessing the realizability of the net deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers projected future taxable income and tax planning strategies in making this assessment. As of December 31, 2020 and 2021, the Company provided a valuation allowance of $135.0 million and $162.0 million, respectively, to reduce the net deferred tax assets due to uncertainty surrounding the realizability of these assets. The increase in the valuation allowance for the year ended December 31, 2021 of $27.0 million was primarily attributable to an increase in losses without benefit. For the year ended December 31, 2021, the Company did not have any offshore earnings of certain non-U.S. subsidiaries which are permanently reinvested outside the United States. The Company does not recognize the impact of a tax position in its financial statements unless the position is more likely than not to be sustained, based on the technical merits of the position. The Company has unrecognized tax benefits of $50.6 million as of December 31, 2021 that, if recognized, would not result in a tax benefit since it would be fully offset with a valuation allowance. The following is a tabular reconciliation of the total amounts of unrecognized tax benefits for the years ended December 31, 2019, 2020 and 2021 (in thousands): ​ ​ ​ ​ Unrecognized tax benefit—December 31, 2019 $ 41,475 Gross increases—tax positions in current year ​ 2,954 Gross increases—tax positions in prior year ​ ​ 870 Unrecognized tax benefit—December 31, 2020 ​ 45,299 Gross increases—tax positions in current year ​ 3,508 Gross increases—tax positions in prior year ​ ​ 2,142 Gross decreases—tax positions in prior year ​ ​ (364) Unrecognized tax benefit—December 31, 2021 ​ $ 50,585 ​ The increase in the Company’s unrecognized tax benefits in the years ended December 31, 2020 is primarily attributable to the portion of AFTC offset by the fuel tax the Company collected from its customers. The increase in the Company’s unrecognized tax benefits in the years ended December 31, 2021 is primarily attributable to the warrants issued to its customer and the portion of AFTC offset by the fuel tax the Company collected from its customers. ASC 740, Income Taxes, The Company is subject to taxation in the United States and various states and foreign jurisdictions. The Company’s tax years for 2018 through 2021 are subject to examination by various tax authorities. Although the Company is no longer subject to U.S. examination for years before 2018, and for state tax examinations for years before 2017, taxing authorities can adjust the net operating losses that arose in earlier years if and when the net operating losses reduce future income. In addition, the Company is required to indemnify SAFE&CEC S.r.l. for taxes that are imposed on CEC for pre-contribution tax periods. A number of years may elapse before an uncertain tax position is finally resolved. It is often difficult to predict the final outcome or the timing of resolution of an uncertain tax position, but the Company believes that its reserves for income taxes reflect the most probable outcomes. The Company adjusts the reserve, as well as the related interest and penalties, in light of changing facts and circumstances. The amount of penalties accrued is immaterial. Settlement of any particular position would usually require the use of cash and result in the reduction of the related reserve, or there could be a change in the amount of the Company’s net operating loss. The resolution of a matter would be recognized as an adjustment to the provision for income taxes at the effective tax rate in the period of resolution. The Company does not expect a significant increase or decrease in its uncertain tax positions within the next twelve months.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 15 —Commitments and Contingencies Environmental Matters The Company is subject to federal, state, local and foreign environmental laws and regulations. The Company does not anticipate any expenditures to comply with such laws and regulations that would have a material impact on the Company’s consolidated financial position, results of operations or liquidity. The Company believes that its operations comply, in all material respects, with applicable federal, state, local and foreign environmental laws and regulations. Litigation, Claims and Contingencies The Company may become party to various legal actions that arise in the ordinary course of its business. The Company is also subject to audit by tax and other authorities for varying periods in various federal, state, local and foreign jurisdictions, and disputes may arise during the course of these audits. It is impossible to determine the ultimate liabilities that the Company may incur resulting from any of these lawsuits, claims, proceedings, audits, commitments, contingencies and related matters or the timing of these liabilities, if any. If these matters were to ultimately be resolved unfavorably, it is possible that such an outcome could have a material adverse effect upon the Company’s consolidated financial position, results of operations, or liquidity. The Company does not, however, anticipate such an outcome and it believes the ultimate resolution of these matters will not have a material adverse effect on the Company’s consolidated financial position, results of operations, or liquidity. Long-Term Take-or-Pay Natural Gas Purchase Contracts The Company has entered into one long-term CNG supply contract to purchase CNG, on a take-or-pay basis, that expires in June 2022. As of December 31, 2021, the fixed commitments under this contract totaled approximately $0.1 million for the year ending December 31, 2022. The Company has entered into quarterly fixed price natural gas purchase contracts with take-or-pay commitments extending through June 2023. As of December 31, 2021, the fixed commitments under these contracts totaled approximately Long-Term Natural Gas Supply Contract In June 2017, the Company’s subsidiary, NG Advantage, entered into an arrangement with bp for the supply, sale and transportation of CNG over a five-year period starting in December 2018 and expiring February 2022 (see Note 4). The arrangement is customary and ordinary course. As of December 31, 2021, the commitments for the specified volume under this contract were estimated to be approximately $1.1 million for the year ending December 31, 2022. bpJV Capital Call Contribution In December 2021, the bpJV authorized a capital call in the amount of $143.2 million with bp

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases
Leases	Note 16 —Leases The Company’s operating leases are comprised of real estate for fueling stations, office spaces, warehouses, a LNG liquefaction plant, and office equipment, and its finance leases are comprised of vehicles. NG Advantage has provided residual value guarantees on leases of certain vehicles aggregating $1.0 million to the lessors. NG Advantage expects to owe these amounts in full and therefore they have been included in the measurement of the lease liabilities and ROU assets. Certain of the Company’s real estate leases contain variable lease payments, including payments based on a change in the index or gasoline gallon equivalents of natural gas dispensed at fueling stations. These variable lease payments cannot be determined at the commencement of the lease, are not included in the ROU assets and lease liabilities, and are recorded as a period expense when incurred. Lessee Accounting As of December 31, 2020 and 2021, the Company’s finance and operating lease asset and liability balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Finance leases: ​ ​ Land, property and equipment, gross ​ $ 4,915 ​ $ 5,617 Accumulated depreciation ​ (1,905) ​ (2,646) Land, property and equipment, net ​ $ 3,010 ​ $ 2,971 ​ ​ ​ ​ ​ ​ ​ Current portion of finance lease obligations ​ $ 840 ​ $ 846 Long-term portion of finance lease obligations ​ 2,552 ​ 2,427 Total finance lease liabilities ​ $ 3,392 ​ $ 3,273 ​ ​ ​ ​ ​ ​ ​ Operating leases: ​ ​ Operating lease right-of-use assets ​ $ 25,967 ​ $ 42,537 ​ ​ ​ ​ ​ ​ ​ Current portion of operating lease obligations ​ $ 2,822 ​ $ 3,551 Long-term portion of operating lease obligations ​ 23,698 ​ 39,431 Total operating lease liabilities ​ $ 26,520 ​ $ 42,982 ​ The components of lease expense for finance and operating leases consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2021 Finance leases: ​ ​ Depreciation on assets under finance leases ​ $ 733 ​ $ 809 Interest on lease liabilities ​ 185 ​ 181 Total finance leases expense ​ $ 918 ​ $ 990 ​ ​ ​ ​ ​ ​ ​ Operating leases: ​ ​ Lease expense ​ $ 6,287 ​ $ 7,313 Lease expense on short-term leases ​ 847 ​ 205 Variable lease expense ​ 2,593 ​ 3,321 Sublease income ​ (736) ​ (726) Total operating leases expense ​ $ 8,991 ​ $ 10,113 ​ Supplemental information on finance and operating leases is as follows (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2021 Operating cash outflows from finance leases ​ $ 185 ​ $ 181 Operating cash outflows from operating leases ​ $ 5,503 ​ $ 5,804 Financing cash outflows from finance leases ​ $ 1,242 ​ $ 789 ​ ​ ​ ​ ​ ​ ​ Assets obtained in exchange for new finance lease liabilities (1) ​ $ 1,337 ​ $ 879 ROU assets obtained in exchange for operating lease liabilities (1) ​ $ 96 ​ $ 19,515 ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2021 Weighted-average remaining lease term - finance leases 3.59 years 2.87 years Weighted-average remaining lease term - operating leases 10.81 years 12.31 years ​ ​ ​ ​ ​ Weighted-average discount rate - finance leases 5.27% 5.22% Weighted-average discount rate - operating leases 8.40% 7.55% (1) These amounts are excluded from the accompanying consolidated statements of cash flows as they are non-cash investing, operating and/or financing activities. The following schedule represents the Company’s maturities of finance and operating lease liabilities as of December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Finance Leases Operating Leases Fiscal year: ​ ​ ​ ​ 2022 ​ $ 990 ​ $ 6,148 2023 ​ 893 ​ 6,037 2024 ​ 1,305 ​ 6,087 2025 ​ 390 ​ 6,028 2026 ​ — ​ 5,840 Thereafter ​ — ​ 38,033 Total minimum lease payments ​ 3,578 ​ 68,173 Less amount representing interest ​ (305) ​ (25,191) Present value of lease liabilities ​ $ 3,273 ​ $ 42,982 ​ Lessor Accounting The Company leases fueling station equipment to customers that contain an option to extend and an end-of-term purchase option. Receivables from these leases are accounted for as finance leases, specifically sales-type leases, and are included in “Other receivables” and “Notes receivable and other long-term assets, net” in the accompanying 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 years ended December 31, 2020 and 2021, the Company recognized $0.5 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 December 31, 2021 (in thousands): ​ ​ ​ ​ ​ Fiscal year: ​ 2022 ​ $ 1,182 2023 ​ 962 2024 ​ 962 2025 ​ 962 2026 ​ 1,034 Thereafter ​ 2,339 Total minimum lease payments ​ 7,441 Less amount representing interest ​ (1,908) Present value of lease receivables ​ $ 5,533 ​

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2021
Retirement Benefits [Abstract]
401(k) Plan	Note 17 – 401(k) Plan The Company has established a savings plan (“Savings Plan”) which is qualified under Section 401(k) of the Internal Revenue Code. Eligible employees may elect to make contributions to the Savings Plan through salary deferrals of up to 90% of their base pay, subject to Internal Revenue Code limitations. The Company may also make discretionary contributions to the Savings Plans, subject to limitations. For each of the years ended December 31, 2019, 2020 and 2021 the Company contributed approximately $1.3 million, $1.5 million and $1.6 million, respectively, of matching contributions to the Savings Plan.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Note 18 – Net Income (Loss) Per Share The following table sets forth the computations of basic and diluted earnings per share for the years ended December 31, 2019, 2020 and 2021 (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Net income (loss) attributable to Clean Energy Fuels Corp. $ 20,421 $ (9,864) $ (93,146) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ ​ 204,573,287 ​ ​ 200,657,912 ​ ​ 213,118,694 Dilutive effect of potential common shares from restricted stock units, stock options and stock warrants ​ ​ 1,414,222 ​ ​ — ​ ​ — Weighted-average common shares outstanding - diluted ​ ​ 205,987,509 ​ ​ 200,657,912 ​ ​ 213,118,694 Basic income (loss) per share ​ $ 0.10 ​ $ (0.05) ​ $ (0.44) Diluted income (loss) per share ​ $ 0.10 ​ $ (0.05) ​ $ (0.44) ​ 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. ​ ​ ​ ​ ​ ​ ​ (in shares) 2019 2020 2021 Stock options 7,652,463 8,142,831 17,153,671 Convertibles notes 3,164,557 1,112,783 — Restricted stock units — 978,716 ​ 1,126,942 Amazon warrant shares ​ — ​ — ​ 58,767,714 Total ​ 10,817,020 ​ 10,234,330 ​ 77,048,327 ​

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Note 19 —Related Party Transactions TotalEnergies S.E. During the years ended December 31, 2020 and 2021, the Company recognized revenue of $7.8 million and $4.9 million, respectively, related to RINs and LNG sold to TotalEnergies and its affiliates in the ordinary course of business, AFTC credits, and settlements on commodity swap contracts (Note 7). As of December 31, 2020 and 2021, the Company had receivables from TotalEnergies of $0.9 million and $1.4 million, respectively. During the years ended December 31, 2020 and 2021, the Company paid TotalEnergies $0.7 million and $2.0 million, respectively, for expenses incurred in the ordinary course of business, settlements on commodity swap contracts (Note 7), and the guaranty fee under the CSA (Note 12). As of December 31, 2020 and 2021, the amount due to TotalEnergies was $0.0 million and $0.1 million, respectively. SAFE&CEC S.r.l During the years ended December 31, 2020 and 2021, the Company received $1.2 million and $0.2 million, respectively, from SAFE&CEC S.r.l. in the ordinary course of business. As of December 31, 2020, the Company had receivables from SAFE&CEC S.r.l. of $0.2 million. Receivables balance as of December 31, 2021 was immaterial. During the years ended December 31, 2020 and 2021, the Company paid SAFE&CEC S.r.l. $4.8 million and $9.6 million, respectively, for parts and equipment in the ordinary course of business. As of December 31, 2020 and 2021, the Company had payables to SAFE&CEC S.r.l. of $0.9 million and $0.2 million, respectively. TotalEnergies JV and bpJV Pursuant to LLC agreements under the TotalEnergies JV and the bpJV, the Company manages the day-to-day operations of RNG projects under the joint ventures in exchange for management fees. During the year ended December 31, 2021, the Company recognized management fee revenue of $0.4 million. As of December 31, 2021, the Company had receivables from the joint ventures of $0.4 million.

Reportable Segments and Geograp

Reportable Segments and Geographic Information	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Reportable Segments and Geographic Information	Note 20 —Reportable Segments and Geographic Information Disclosures are required for certain information regarding operating segments, products and services, geographic areas of operation and major customers. Segment reporting is based on the “management approach,” which assesses, how management organizes the Company’s operating segments for which separate financial information is (1) available and (2) evaluated regularly by the Chief Operating Decision Maker (“CODM”) in deciding how to allocate resources and in assessing performance. The Company’s CODM is its Chief Executive Officer. The Company operates in a single segment to supply natural gas. In making operating decisions, the CODM primarily considers consolidated financial information, accompanied by volumes delivered information. The assessment of operating results and the allocation of resources among the components of the business are made by the CODM and are based on gross margins and volumes delivered by market sector and volume type. Contracts are evaluated based on the economics of a mix of products and services for a customer. The table below presents the Company’s revenue, operating income (loss) and long-lived assets by geographic area (in thousands). Several of the Company’s functions, including marketing, engineering, and finance are performed at the corporate level. As a result, significant interdependence and overlap exists among the Company’s geographic areas. Geographic revenue data reflect internal allocations and are therefore subject to certain assumptions and the Company’s methodology. Accordingly, revenue, operating income (loss), and long-lived assets shown for each geographic area may not be the amounts that would have been reported if the geographic areas were independent of one another. Revenue by geographic area is categorized based on where services are rendered and finished goods are sold. Operating income (loss) by geographic area is categorized based on the location of the entity selling the finished goods or providing the services. Long-lived assets by geographic are categorized based on the location of the assets. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Revenue: ​ ​ ​ United States ​ $ 338,549 ​ $ 281,546 ​ $ 252,310 Canada ​ 5,516 ​ 10,178 ​ 3,336 Total revenue ​ $ 344,065 ​ $ 291,724 ​ $ 255,646 Operating income (loss): ​ ​ ​ United States ​ $ 10,805 ​ $ (9,853) ​ $ (94,157) Canada ​ (877) ​ 9 ​ (891) Total operating income (loss) ​ $ 9,928 ​ $ (9,844) ​ $ (95,048) Long-lived assets: ​ ​ ​ United States ​ $ 415,548 ​ $ 383,463 ​ $ 440,770 Canada ​ 226 ​ 202 ​ 630 Total long-lived assets ​ $ 415,774 ​ $ 383,665 ​ $ 441,400 ​ The Company’s goodwill and intangible assets as of December 31, 2019, 2020 and 2021 relate to its United States operations, and its subsidiaries, Clean Energy Cryogenics and NG Advantage (see Note 4).

Concentrations

Concentrations	12 Months Ended
	Dec. 31, 2021
Concentrations [Abstract]
Concentrations	Note 21 —Concentrations During the years ended December 31, 2019, 2020 and 2021, one three During the years ended December 31, 2019, 2020 and 2021, no single customer accounted for 10% or more of the Company’s total revenue.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Note 22 —Subsequent Events NG Advantage Debt Refinancing In January 2022, NG Advantage entered into a second amendment to the Berkshire ALA pursuant to which Berkshire Bank agreed to lend NG Advantage $14.0 million (the “Berkshire Term Loan 2”). The Berkshire Term Loan 2 bears interest at 5.00% with principal and interest payable in 59 equal monthly installments and a balloon payment due on January 31, 2027. The debt is collateralized by various trailers and station assets of NG Advantage. In connection with the Berkshire Term Loan 2, NG Advantage extinguished $11.1 million of existing debt obligations consisting of $10.4 million in cash payoffs and an application of $0.8 million in deposits held with the former lenders. In connection with the second amendment to the Berkshire ALA, Berkshire Bank released $7.0 million, classified in “Restricted cash” on the accompanying consolidated balance sheet, to the Company related to the Company’s limited guaranty under the Berkshire ALA. Concurrently, the Company issued an irrevocable standby letter of credit to Berkshire Bank for $7.0 million as collateral under the second amendment to the Berkshire ALA. The standby letter of credit is valid until specified release conditions are satisfied and is collateralized by the Company’s revolving line of credit, reducing the total amount available under the line of credit to $11.0 million. Stock Repurchase Activities Subsequent to December 31, 2021, through the date of filing of this Report (the "filing date"), the Company repurchased 511,010 shares of its common stock under the Repurchase Program for a total cost of $3.0 million (exclusive of fees and commissions) at an average price of $5.85 per share. As of the filing date, the Company had utilized a total of $20.4 million to repurchase shares of its common stock in the open market and had a total of $29.6 million of authorized funds remaining under the Repurchase Program.

Schedule II_ Valuation and Qual

Schedule II: Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II: Valuation and Qualifying Accounts	Schedule II - Valuation and Qualifying Accounts ​ ​ ​ ​ ​ ​ ​ ​ ​ (In thousands) ​ Allowance for Allowance for ​ ​ Credit Losses ​ Credit Losses ​ ​ on Accounts ​ on Notes ​ ​ Receivables ​ Receivables Balance as of December 31, 2018 ​ $ 1,919 ​ $ 4,163 Charges (benefit) to operations ​ 908 ​ 931 Deductions ​ (415) ​ (1,763) Balance as of December 31, 2019 ​ 2,412 ​ 3,331 Charges (benefit) to operations ​ 796 ​ 1,250 Deductions ​ (1,873) ​ (476) Balance as of December 31, 2020 ​ 1,335 ​ 4,105 Charges (benefit) to operations ​ 77 ​ 650 Deductions ​ (207) ​ — Balance as of December 31, 2021 ​ $ 1,205 ​ $ 4,755

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying 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, results of operations, comprehensive income (loss) and cash flows in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying 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 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, stock-based compensation expense and stock-based sales incentive charges.
Inventory	Inventory Inventory consists of raw materials and spare parts, work in process and finished goods and is stated at the lower of cost (first-in, first-out) or net realizable value. The Company evaluates inventory balances for excess quantities and obsolescence by analyzing estimated demand, inventory on hand, sales levels and other information and reduces inventory balances to net realizable value for excess and obsolete inventory based on this analysis. ​ Inventories consisted of the following as of December 31, 2020 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Raw materials and spare parts ​ $ 28,100 ​ $ 31,302 Total inventory ​ $ 28,100 ​ $ 31,302 ​
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities In connection with the Company’s Zero Now Zero Now
Property and Equipment	Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization are recognized over the estimated useful lives of the assets using the straight-line method. The estimated useful lives of depreciable assets are three LNG trailers three
Leases	Leases On January 1, 2019, the Company adopted Accounting Standards Codification (“ASC”) 842, Leases At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether the Company obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether the Company has the right to direct the use of the asset. The commencement date of the contract is the date the lessor makes the underlying asset available for use by the lessee. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less; the Company recognizes lease expense for these leases on a straight-line basis over the lease term. As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease. The lease classification affects the expense recognition on the consolidated statements of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, whereby depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting.
Long-Lived Assets	Long-Lived Assets The Company reviews the carrying value of its long-lived assets, including property and equipment and intangible assets with finite useful lives, for impairment whenever events or changes in circumstances indicate that the carrying value of an asset or asset group may not be recoverable. Events that could result in an impairment review include, among others, a significant decrease in the operating performance of a long-lived asset or asset group or the decision to close a fueling station. Impairment testing involves a comparison of the sum of the undiscounted future cash flows of the asset or asset group to its carrying amount. If the sum of the undiscounted future cash flows exceeds the carrying amount, then no impairment exists. If the carrying amount exceeds the sum of the undiscounted future cash flows, then a second step is performed to determine the amount of impairment, if any, to be recognized. An impairment loss is recognized to the extent that the carrying amount of the asset or asset group exceeds its fair value. The fair value of the asset or asset group is based on estimated discounted future cash flows of the asset or asset group using a discount rate commensurate with the related risk. The estimate of future cash flows requires management to make assumptions and to apply judgment, including forecasting future sales and expenses and estimating useful lives of the assets. These estimates can be affected by a number of factors, including, among others, future results, demand, and economic conditions, many of which can be difficult to predict. There were no impairments of the Company’s long-lived assets in the years ended December 31, 2019, 2020 and 2021. Intangible assets with finite useful lives are amortized over their respective estimated useful lives using the straight-line method. The estimated useful lives of intangible assets with finite useful lives are from one one two The Company’s intangible assets as of December 31, 2020 and 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Customer relationships ​ $ 5,376 ​ $ 5,376 Acquired contracts ​ 4,384 ​ 9,884 Trademark and trade names ​ 2,700 ​ 2,700 Non-compete agreements ​ 860 ​ 860 Total intangible assets ​ 13,320 ​ 18,820 Less accumulated amortization ​ (12,856) ​ (13,320) Net intangible assets ​ $ 464 ​ $ 5,500 ​ Amortization expense for intangible assets was $1.0 million, $0.8 million, and $0.5 million for the years ended December 31, 2019, 2020, and 2021, respectively. In 2021, the Company acquired contractual rights to manure feedstock for an anaerobic digester gas (“ADG”) RNG production project totaling $5.5 million. The acquired manure rights have an initial term of 20 years. Amounts are classified and included under “Acquired contracts” in the table above. As of December 31, 2021, the Company paid $1.0 million and accrued $4.5 million, which was included in “Accrued liabilities” in the accompanying consolidated balance sheets, related to the acquired manure rights. The $4.5 million was excluded from the accompanying consolidated statements of cash flows as it was a non-cash investing activity. The intangible asset related to manure rights will be amortized over the contractual term of 20 years using the straight-line method with amortization commencing on the date of commercial operation of the ADG RNG facility. Estimated amortization expense subsequent to the year ended December 31, 2021 is expected to be approximately $0.0 million in 2022, $0.0 million in 2023, $0.3 million in 2024, $0.3 million in 2025, $0.3 million in 2026, and $4.6 million thereafter.
Goodwill	Goodwill Goodwill represents the excess of costs incurred over the fair value of the net assets of acquired businesses. The Company assesses its goodwill using either a qualitative or quantitative approach to determine whether it is more likely than not that the fair value of its reporting unit is less than its carrying value. The Company is required to use judgment when applying the goodwill impairment test, including, among other considerations, the identification of reporting unit(s), the assessment of qualitative factors, and the estimation of fair value of a reporting unit in the quantitative approach. The Company determined that it is a single reporting unit for the purpose of goodwill impairment tests. The Company performs the impairment test annually on October 1, or more frequently if facts and circumstances warrant a review. The qualitative goodwill assessment includes the potential impact on a reporting unit’s fair value of certain events and circumstances, including its enterprise value, macroeconomic conditions, industry and market considerations, cost factors, and other relevant entity-specific events. If it is determined, based upon the qualitative assessment, that it is more likely than not that the reporting unit’s fair value is less than its carrying amount, then a quantitative impairment test is performed. The quantitative assessment estimates the reporting unit’s fair value based on its enterprise value plus an assumed control premium as evidence of fair value. The estimates used to determine the fair value of the reporting unit may change based on results of operations, macroeconomic conditions, stock price fluctuations, or other factors. Changes in these estimates could materially affect our assessment of the fair value and goodwill impairment for the reporting unit. During the years ended The following table summarizes the activity related to the carrying amount of goodwill (in thousands): ​ ​ ​ ​ Balance as of December 31, 2019 ​ $ 64,328 Balance as of December 31, 2020 ​ $ 64,328 Balance as of December 31, 2021 ​ $ 64,328
Revenue Recognition	Revenue Recognition ​ 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 them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities. ​ Volume-Related The Company’s volume-related revenue primarily consists of sales of RNG and conventional natural gas, in the form of CNG and LNG, O&M services and RINs and LCFS Credits in addition to Amazon Warrant Charges and changes in fair value of the Company’s derivative instruments associated with providing fuel to customers under contracts. Fuel and O&M services are sold pursuant to contractual commitments over defined goods-and-service delivery periods. These contracts typically include a stand-ready obligation to supply natural gas and/or provide O&M services daily based on a committed and agreed upon routine maintenance schedule or when and if called upon by the customer. The Company applies the ‘right to invoice’ practical expedient and recognizes fuel and O&M services revenue in the amount to which the Company has the right to invoice. The Company has a right to consideration based on the amount of gasoline gallon equivalents of fuel dispensed by the customer and current pricing conditions, which are typically billed to the customer on a monthly basis. Since payment terms are less than a year, the Company has elected the practical expedient which allows it to not assess whether a customer contract has a significant financing component. Contract modifications are not distinct from the existing contract and are typically renewals of fuel and O&M service sales. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price is recognized prospectively. The Company sells RINs and LCFS Credits to third parties that need the credits to comply with federal and state requirements. Revenue is recognized on these credits when there is an agreement in place to monetize the credits at a determinable price. Amazon Warrant Charges (defined in Note 13) are determined based on the grant date fair value of the award and the associated non-cash stock-based sales incentive charges, which are recorded as a reduction of revenue and are recognized as the customer purchases fuel and vesting conditions become probable of being achieved. See discussion under “Amazon Warrant” below and Note 13 for additional information. The changes in fair value of derivative instruments relate to the Company’s commodity swap and customer fueling contracts. The contracts are measured at fair value with changes in fair value recorded in the accompanying consolidated statements of operations in the period incurred. 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 existing and anticipated customer fueling contracts under the Company’s Zero Now Station Construction Sales Station construction contracts are generally short-term, except for certain larger and more complex stations, which can take up to 24 months to complete. For most of the Company’s station construction contracts, the customer contracts with the Company to provide a significant service of integrating a complex set of tasks and components into a single station. Hence, the entire contract is accounted for as one performance obligation. The Company recognizes revenue over time as the Company performs under its station construction contracts because of the continual transfer of control of the goods to the customer, who typically controls the work in process. Revenue is recognized based on the extent of progress towards completion of the performance obligation and is recorded proportionally as costs are incurred. Costs to fulfill the Company’s obligations under these contracts typically include labor, materials and subcontractors’ costs, other direct costs and an allocation of indirect costs. Refinements of estimates to account for changing conditions and new developments are continuous and characteristic of the process. Many factors that can affect contract profitability may change during the performance period of the contract, including differing site conditions, the availability of skilled contract labor, the performance of major suppliers and subcontractors, and unexpected changes in material costs. Because a significant change in one or more of these estimates could affect the profitability of these contracts, the contract price and cost estimates are reviewed periodically as work progresses and adjustments proportionate to the cost-to-cost measure of progress are reflected in contract revenues in the reporting period when such estimates are revised. Provisions for estimated losses on uncompleted contracts are recorded in the period in which the losses become known. Contract modifications are typically expansions in scope of an existing station construction project. As a result, these modifications are accounted for as if they were part of the existing contract. The effect of a contract modification on the transaction price and the Company’s measure of progress for the performance obligation to which it relates is recognized as an adjustment to revenue (either as an increase or a reduction) on a cumulative catch-up basis. Under the typical payment terms of the Company’s station construction contracts, the customer makes either performance-based payments (“PBPs”) or progress payments. PBPs are interim payments of the contract price based on quantifiable measures of performance or the achievement of specified events or milestones. Progress payments are interim payments of costs incurred as the work progresses. For some of these contracts, the Company may be entitled to receive an advance payment. The advance payment typically is not considered a significant financing component because it is used to meet working capital demands that can be higher in the early stages of a construction contract and to protect the Company if the customer fails to adequately complete some or all of its obligations under the contract. In addition, the customer retains a small portion of the contract price until completion of the contract. Such retained portion of the contract price is not considered a significant financing component because the intent is to protect the customer. In certain contracts with its customers, the Company agrees to provide multiple goods or services, including construction of and sale of a station, O&M services, and sale of fuel to the customer. These contracts have multiple performance obligations because the promise to transfer each separate good or service is separately identifiable and is distinct. This evaluation requires significant judgment and the decision to combine a group of contracts or separate the combined or single contract into multiple performance obligations could change the amount of revenue recognized in one or more periods. The Company allocates the contract price to each performance obligation using best estimates of the standalone selling price of each distinct good or service in the contract. The primary method used to estimate the standalone selling price for fuel and O&M services is observable standalone sales, and the primary method used to estimate the standalone selling price for station construction sales is the expected cost plus a margin approach because the Company sells customized customer-specific solutions. Under this approach, the Company forecasts expected costs of satisfying a performance obligation and then adds an appropriate margin for the good or service. ​ AFTC See discussion under “Alternative Fuel Tax Credit” below for more information about AFTC, which is not recognized as revenue until the period the credit is authorized through federal legislation. Other The majority of other revenue is from sales of used natural gas heavy-duty trucks purchased by the Company. Revenue on these contracts is recognized at the point in time when the customer accepts delivery of the truck.
Alternative Fuels Tax Credit	Alternative Fuel Tax Credit Under separate pieces of U.S. federal legislation, the Company has been eligible to receive a federal alternative fuels tax credit (“AFTC”) for its natural gas vehicle fuel sales made between October 1, 2006 and December 31, 2021. The AFTC, which had previously expired on December 31, 2016, was reinstated on February 9, 2018 to apply retroactively to vehicle fuel sales made from January 1, 2017 through December 31, 2017. On December 20, 2019, AFTC was retroactively extended beginning January 1, 2018 through December 31, 2020 and subsequently extended for vehicle fuel sales made through December 31, 2021. As a result of the 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 year ended December 31, 2019. AFTC was extended in December 2020 and is currently available for vehicle fuel sales made through December 31, 2021. The AFTC credit is equal to $0.50 per gasoline gallon equivalent of CNG that the Company sold as vehicle fuel, and $0.50 per diesel gallon of LNG that the Company sold as vehicle fuel in 2019, 2020 and 2021. Based on the service relationship with its customers, either the Company or its customer claims the credit. The Company records its AFTC credits, if any, as revenue in its consolidated statements of operations because the credits are fully payable to the Company and do not offset income tax liabilities. As such, the credits are not deemed income tax credits under the accounting guidance applicable to income taxes.
LNG Transportation Costs	LNG Transportation Costs The Company records the costs incurred to transport LNG to its customers in “Product cost of sales” in the accompanying consolidated statements of operations.
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred. Advertising costs were $1.2 million, $0.0 million and $0.0 million for the years ended December 31, 2019, 2020 and 2021, respectively.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes compensation expense for all stock‑based payment arrangements over the requisite service period of the award and recognizes forfeitures as they occur. For stock options, the Company determines the grant date fair value using the Black‑Scholes option pricing model, which requires the input of certain assumptions, including the expected life of the stock‑based payment award, stock price volatility and risk‑free interest rate. For restricted stock units, the Company determines the grant date fair value based on the closing market price of its common stock on the date of grant.
Amazon Warrant	Amazon Warrant The Amazon Warrant (as defined in Note 13) is accounted for as an equity instrument and measured in accordance with Accounting Standards Codification (“ASC”) 718, Compensation – Stock Compensation the transaction price in accordance with ASC 606, Revenue from Contracts with Customers
Income Taxes	Income Taxes Income taxes are computed using the asset and liability method. Under this method, deferred income taxes are recognized by applying enacted statutory tax rates applicable to future years to differences between the tax bases and financial carrying amounts of existing assets and liabilities. The impact on deferred taxes of changes in tax rates and laws, if any, are applied to the years during which temporary differences are expected to be settled and are reflected in the consolidated financial statements in the period of enactment. Valuation allowances are established when management determines it is more likely than not that deferred tax assets will not be realized. When evaluating the need for a valuation analysis, we use estimates involving a high degree of judgment including projected future US GAAP income and the amounts and estimated timing of the reversal of any deferred tax assets and liabilities. The Company has a recognition threshold and a measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities based on the technical merits of the position. The amount recognized is measured as the largest amount of benefit that has a greater than 50 percent likelihood of being realized upon ultimate settlement. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefit in income tax expense. The Company operates within multiple domestic and foreign taxing jurisdictions and is subject to audit in these jurisdictions. These audits can involve complex issues, which may require an extended period of time to resolve. Although the Company believes that adequate consideration has been given to these issues, it is possible that the ultimate resolution of these issues could be significantly different from originally estimated.
Net Income (Loss) Per Share	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.
Foreign Currency Translation and Transactions	Foreign Currency Translation and Transactions The Company uses the local currency as the functional currency of its foreign subsidiary and equity method investment. Accordingly, all assets and liabilities outside the United States are translated into U.S. dollars at the rate of exchange in effect at the balance sheet date. Revenue and expense items are translated at the weighted-average exchange rates prevailing during the period. Foreign currency translation adjustments are recorded as accumulated other comprehensive income (loss) in stockholders’ equity. Foreign currency transactions occur when there is a transaction denominated in other than the respective entity’s functional currency. The Company records the changes in the exchange rate for these transactions in its consolidated statements of operations. For each of the years ended December 31, 2019, 2020 and 2021, foreign exchange transaction gains and (losses) were included in “Other income (expense), net” in the accompanying consolidated statements of operations and were $0.0 million.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity (net assets) of a business enterprise during the period from transactions and other events and circumstances from non-owner sources. The difference between net income (loss) and comprehensive income (loss) for the years ended December 31, 2019, 2020 and 2021 was comprised of the Company’s foreign currency translation adjustments and unrealized gains and losses on available-for-sale securities.
Concentration of Credit Risk	Concentration of Credit Risk Credit is extended to all customers based on financial condition, and collateral is generally not required. Concentrations of credit risk with respect to trade receivables are limited because of the large number of customers comprising the Company’s customer base and dispersion across many different industries and geographies. Certain international customers, however, have historically been slower to pay on trade receivables. Accordingly, the Company continually monitors collections and payments from its customers and maintains a provision for estimated credit losses based upon its historical experience and any specific customer collection issues that it has identified. Although credit losses have historically been within the Company’s expectations and the provisions established, the Company cannot guarantee that it will continue to experience the same credit loss rates that it has in the past.
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Recently Issued Accounting Pronouncements In July 2021, the FASB issued ASU No. 2021-05, Leases (Topic 842): Lessors–Certain Leases with Variable Lease Payments In November 2021, the FASB issued ASU No. 2021-10, Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance 15, 2021, with early adoption permitted. The Company is currently evaluating the impact of adopting this new ASU and does not expect the update to have a material impact on its consolidated financial statements and related disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of inventories	​ Inventories consisted of the following as of December 31, 2020 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Raw materials and spare parts ​ $ 28,100 ​ $ 31,302 Total inventory ​ $ 28,100 ​ $ 31,302 ​
Schedule of finite-lived intangible assets	The Company’s intangible assets as of December 31, 2020 and 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Customer relationships ​ $ 5,376 ​ $ 5,376 Acquired contracts ​ 4,384 ​ 9,884 Trademark and trade names ​ 2,700 ​ 2,700 Non-compete agreements ​ 860 ​ 860 Total intangible assets ​ 13,320 ​ 18,820 Less accumulated amortization ​ (12,856) ​ (13,320) Net intangible assets ​ $ 464 ​ $ 5,500
Schedule of goodwill	The following table summarizes the activity related to the carrying amount of goodwill (in thousands): ​ ​ ​ ​ Balance as of December 31, 2019 ​ $ 64,328 Balance as of December 31, 2020 ​ $ 64,328 Balance as of December 31, 2021 ​ $ 64,328

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	The table below presents the Company’s revenue disaggregated by revenue source (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years Ended December 31, ​ 2019 2020 2021 Volume-related (1) (2) ​ $ 273,535 ​ $ 245,300 ​ $ 218,540 Station construction sales ​ 23,120 ​ 26,593 ​ 16,406 AFTC (3) ​ 47,123 ​ 19,831 ​ 20,700 Other ​ 287 ​ — ​ — Total revenue ​ $ 344,065 ​ $ 291,724 ​ $ 255,646 ​ (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. See Note 1 and Note 7 for more information about these derivative instruments. For the years ended December 31, 2019, 2020 and 2021, changes in the fair value of commodity swaps and customer fueling contracts amounted to a loss of $6.6 million, a gain of $2.1 million, and a loss of $3.5 million, respectively. (2) Includes non-cash stock-based sales incentive contra-revenue charges associated with the Amazon Warrant for the years ended December 31, 2019, 2020 and 2021 of $0.0 million, $0.0 million and $83.6 million, respectively. See Note 13 for more information. (3) Represents the federal alternative fuel excise tax credit that we refer to as “AFTC,” which was extended for vehicle fuel sales made beginning January 1, 2021 through December 31, 2021.
Summary of contract balances	As of December 31, 2020 and 2021, the Company’s contract balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 ​ ​ ​ ​ ​ ​ ​ Accounts receivable, net ​ $ 61,784 ​ $ 87,433 ​ ​ ​ ​ ​ ​ Contract assets - current ​ $ 729 ​ $ 966 Contract assets - non-current ​ 3,998 ​ 3,532 Contract assets - total ​ $ 4,727 ​ $ 4,498 ​ ​ ​ ​ ​ ​ Contract liabilities - current ​ $ 1,638 ​ $ 5,523 Contract liabilities - non-current ​ 59 ​ — Contract liabilities - total ​ $ 1,697 ​ $ 5,523

Investments in Other Entities_2

Investments in Other Entities and Noncontrolling Interest in a Subsidiary (Tables)	12 Months Ended
	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Summary of financial information	Combined summarized financial information for the Company’s other equity method investments is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2020 ​ 2021 Revenue ​ $ 546 ​ $ 463 ​ $ 704 Gross profit ​ $ 178 ​ $ 155 ​ $ 216 Operating loss ​ $ (214) ​ $ (90) ​ $ (1,757) Net loss ​ $ (250) ​ $ (126) ​ $ (1,793) ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2020 ​ 2021 Current assets ​ $ 1,233 ​ $ 1,349 Non-current assets ​ 5,553 ​ 7,047 Total assets ​ $ 6,786 ​ $ 8,396 ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ $ 1,421 ​ $ 1,012 Non-current liabilities ​ 66 ​ 192 Total liabilities ​ $ 1,487 ​ $ 1,204
TotalEnergies
Schedule of Equity Method Investments [Line Items]
Summary of financial information	The following table presents combined summarized financial information for the TotalEnergies JV (in thousands): ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 Revenue ​ $ — Gross profit ​ $ — Operating loss ​ $ (119) Net loss ​ $ (119) ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 Current assets ​ $ 3,086 Non-current assets ​ 13,103 Total assets ​ $ 16,189 ​ ​ ​ ​ Current liabilities ​ $ 6,770 Non-current liabilities ​ — Total liabilities ​ $ 6,770
bpJV
Schedule of Equity Method Investments [Line Items]
Summary of financial information	Combined summarized financial information for the bpJV is as follows (in thousands): ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2021 Revenue ​ $ — Gross profit ​ $ — Operating loss ​ $ (678) Net loss ​ $ (603) Net loss attributable to bpJV ​ $ (599) ​ ​ ​ ​ ​ As of December 31, ​ ​ 2021 Current assets $ 152,072 Non-current assets ​ ​ 70,433 Total assets ​ $ 222,505 ​ ​ ​ ​ Current liabilities ​ $ 24,932 Non-current liabilities ​ ​ 1,000 Total liabilities ​ $ 25,932 ​ ​ ​ ​ Equity attributable to shareowners of bpJV ​ $ 191,170 Equity attributable to noncontrolling interest ​ ​ 5,403 Total equity ​ $ 196,573
SAFE&CEC S.r.l.
Schedule of Equity Method Investments [Line Items]
Summary of financial information	Summarized financial information for SAFE&CEC S.r.l. is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2020 ​ 2021 Revenue ​ $ 80,886 ​ $ 89,535 ​ $ 109,119 Gross profit ​ $ 20,525 ​ $ 19,008 ​ $ 25,784 Operating income ​ $ 1,207 ​ $ 609 ​ $ 4,728 Net income (loss) ​ $ 93 ​ $ (306) ​ $ 2,392 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ ​ ​ 2020 ​ 2021 Current assets ​ ​ ​ $ 60,406 ​ $ 75,137 Non-current assets ​ ​ ​ ​ ​ 58,140 ​ ​ 56,052 Total assets ​ ​ ​ ​ $ 118,546 ​ $ 131,189 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Current liabilities ​ ​ ​ ​ $ 55,780 ​ $ 58,910 Non-current liabilities ​ ​ ​ ​ ​ 11,808 ​ ​ 21,730 Total liabilities ​ ​ ​ ​ $ 67,588 ​ $ 80,640

Cash, Cash Equivalents, and R_2

Cash, Cash Equivalents, and Restricted Cash (Tables)	12 Months Ended
	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Schedule of cash and cash equivalents	Cash, cash equivalents and restricted cash as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Current assets: ​ ​ Cash and cash equivalents ​ $ 108,977 ​ $ 99,448 Total cash and cash equivalents ​ $ 108,977 ​ $ 99,448 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ — Restricted cash - held as collateral ​ ​ 7,000 ​ ​ 7,008 Total restricted cash ​ $ 11,000 ​ $ 7,008 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 119,977 ​ $ 106,456
Schedule of components of restricted cash	Cash, cash equivalents and restricted cash as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Current assets: ​ ​ Cash and cash equivalents ​ $ 108,977 ​ $ 99,448 Total cash and cash equivalents ​ $ 108,977 ​ $ 99,448 ​ ​ ​ ​ ​ ​ ​ Long-term assets: ​ ​ Restricted cash - standby letters of credit ​ $ 4,000 ​ $ — Restricted cash - held as collateral ​ ​ 7,000 ​ ​ 7,008 Total restricted cash ​ $ 11,000 ​ $ 7,008 ​ ​ ​ ​ ​ ​ ​ Total cash, cash equivalents and restricted cash ​ $ 119,977 ​ $ 106,456 ​

Short-Term Investments (Tables)

Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of short-term investments	Short-term investments as of December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Gain (Loss) Fair Value Municipal bonds and notes ​ $ 28,998 ​ $ — ​ $ 28,998 Certificates of deposit ​ 530 ​ — ​ 530 Total short-term investments ​ $ 29,528 ​ $ — ​ $ 29,528 ​ Short-term investments as of December 31, 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Estimated ​ Cost Loss Fair Value Municipal bonds and notes ​ $ 6,001 ​ $ (1) ​ $ 6,000 Zero coupon bonds ​ ​ 123,210 ​ ​ (18) ​ ​ 123,192 Certificates of deposit ​ ​ 530 ​ ​ — ​ ​ 530 Total short-term investments ​ $ 129,741 ​ $ (19) ​ $ 129,722

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of commodity derivative activity	Derivatives and embedded derivatives as of December 31, 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 ​ $ 1,591 ​ $ — ​ $ 1,591 Long-term portion of derivative assets, related party ​ ​ 4,057 ​ ​ ​ ​ ​ 4,057 Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ ​ 249 ​ ​ — ​ ​ 249 Notes receivable and other long-term assets, net ​ ​ 542 ​ ​ — ​ ​ 542 Total derivative assets ​ $ 6,439 ​ $ — ​ $ 6,439 Liabilities: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Accrued liabilities ​ $ 283 ​ $ — ​ $ 283 Other long-term liabilities ​ ​ 273 ​ ​ — ​ ​ 273 Total derivative liabilities ​ $ 556 ​ $ — ​ $ 556 ​ Derivatives and embedded derivatives as of December 31, 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross Amounts ​ Gross Amounts ​ Net Amount ​ Recognized Offset Presented Assets: ​ ​ ​ Fueling agreements: ​ ​ ​ ​ ​ ​ ​ ​ ​ Prepaid expenses and other current assets ​ $ 2,038 ​ $ — ​ $ 2,038 Notes receivable and other long-term assets, net ​ ​ 4,738 ​ ​ — ​ ​ 4,738 Total derivative assets ​ $ 6,776 ​ $ — ​ $ 6,776 Liabilities: ​ ​ ​ Commodity swaps: ​ ​ ​ ​ ​ ​ ​ ​ ​ Current portion of derivative liabilities, related party ​ $ 1,900 ​ $ — ​ $ 1,900 Long-term portion of derivative liabilities, related party ​ ​ 2,483 ​ ​ ​ ​ ​ 2,483 Total derivative liabilities ​ $ 4,383 ​ $ — ​ $ 4,383
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, 2020 and 2021, by year with associated volumes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 ​ ​ Volumes ​ Weighted-Average Price per ​ Volumes ​ Weighted-Average Price per Year (Diesel Gallons) Diesel Gallon (Diesel Gallons) Diesel Gallon 2021 ​ 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)	12 Months Ended
	Dec. 31, 2021
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, 2020 and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13 ​ The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13
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, 2020 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 Level 1 Level 2 Level 3 Assets: ​ ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 28,998 ​ $ — ​ $ 28,998 ​ $ — Certificates of deposit (1) ​ 530 ​ — ​ 530 ​ — Commodity swap contracts (2) ​ ​ 5,648 ​ — ​ — ​ 5,648 Embedded derivatives (3) ​ ​ 791 ​ ​ — ​ ​ — ​ ​ 791 Liabilities: ​ ​ ​ ​ ​ Embedded derivatives (3) ​ $ 556 ​ $ — ​ $ — ​ $ 556 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 Level 1 Level 2 Level 3 Assets: ​ ​ ​ Available-for-sale securities (1) ​ ​ ​ ​ Municipal bonds and notes ​ $ 6,000 ​ $ — ​ $ 6,000 ​ $ — Zero coupon bonds ​ 123,192 ​ — ​ 123,192 ​ — Certificates of deposit (1) ​ ​ 530 ​ ​ — ​ ​ 530 ​ ​ — Embedded derivatives (3) ​ ​ 6,776 ​ ​ — ​ ​ — ​ ​ 6,776 Liabilities: ​ ​ ​ ​ ​ ​ ​ ​ Commodity swap contracts (2) ​ $ 4,383 ​ $ — ​ $ — ​ $ 4,383 (1) Included in “Short-term investments” in the accompanying consolidated balance sheets. See Note 6 for more information. (2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” as of December 31, 2020, and “Derivative liabilities, related party” and “Long-term portion of derivative liabilities, related party” as of December 31, 2021, in the accompanying consolidated balance sheets. See Note 7 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” as of December 31, 2020, and "Prepaid expenses and other current assets" and "Notes receivable and other long-term assets, net" as of December 31, 2021 in the accompanying consolidated balance sheets. See Note 7 for more information.
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 table provides a reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis as shown in the tables above that used significant unobservable inputs (Level 3), 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 December 31, 2019 ​ $ 3,270 ​ $ 723 ​ $ (164) ​ $ (81) ​ $ (40) Settlements, net ​ ​ (1,652) ​ ​ — ​ ​ 56 ​ ​ — ​ ​ — Total gain (loss) ​ 4,030 ​ ​ 68 ​ ​ 108 ​ ​ (475) ​ ​ 40 Balance as of December 31, 2020 ​ $ 5,648 ​ $ 791 ​ $ — ​ $ (556) ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance as of December 31, 2020 ​ $ 5,648 ​ $ 791 ​ $ — ​ $ (556) ​ $ — Settlements, net ​ ​ (225) ​ ​ — ​ ​ 1,083 ​ ​ — ​ ​ — Total gain (loss) ​ (5,423) ​ ​ 5,985 ​ ​ (5,466) ​ ​ 556 ​ ​ — Balance as of December 31, 2021 ​ $ — ​ $ 6,776 ​ $ (4,383) ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Change in unrealized gain (loss) for the year ended December 31, 2020 included in earnings ​ $ 2,378 ​ $ 68 ​ $ 164 ​ $ (475) ​ $ 40 Change in unrealized gain (loss) for the year ended December 31, 2021 included in earnings ​ $ (5,648) ​ $ 5,985 ​ $ (4,383) ​ $ 556 ​ $ —

Other Receivables (Tables)

Other Receivables (Tables)	12 Months Ended
	Dec. 31, 2021
Receivables [Abstract]
Schedule of other receivables	Other receivables as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Loans to customers to finance vehicle purchases ​ $ 394 ​ $ 419 Accrued customer billings ​ 6,335 ​ 4,417 Fuel tax credits ​ 10,556 ​ 12,684 Other ​ 6,370 ​ 6,927 Total other receivables ​ $ 23,655 ​ $ 24,447

Land, Property and Equipment (T

Land, Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Summary of land, property and equipment	Land, property and equipment, net as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Land ​ $ 3,476 ​ $ 3,476 LNG liquefaction plants ​ 94,633 ​ 94,633 Station equipment ​ 344,839 ​ 354,699 Trailers ​ 79,860 ​ 72,783 Other equipment ​ 89,276 ​ 93,135 Construction in progress ​ 73,272 ​ 74,963 ​ ​ 685,356 ​ 693,689 Less accumulated depreciation ​ (394,445) ​ (431,928) Total land, property and equipment, net ​ $ 290,911 ​ $ 261,761 ​

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2021
Payables and Accruals [Abstract]
Schedule of accrued liabilities	Accrued liabilities as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Accrued alternative fuels incentives (1) ​ $ 18,175 ​ $ 28,106 Accrued employee benefits ​ 4,282 ​ 4,547 Accrued gas and equipment purchases ​ 9,897 ​ 17,158 Accrued interest ​ 512 ​ 893 Accrued property and other taxes ​ 3,094 ​ 3,369 Accrued salaries and wages ​ 7,646 ​ 8,172 Embedded derivatives ​ ​ 283 ​ ​ — Other (2) ​ 8,748 ​ 12,914 Total accrued liabilities ​ $ 52,637 ​ $ 75,159 (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)	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Schedule of long-term debt	Debt obligations as of December 31, 2020 and 2021 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs bp Loan ​ $ 50,000 $ — ​ $ 50,000 NG Advantage debt ​ 29,535 ​ 117 ​ 29,418 SG Facility ​ ​ 5,100 ​ ​ — ​ ​ 5,100 Other debt ​ 1,162 ​ — ​ 1,162 Total debt ​ 85,797 ​ 117 ​ 85,680 Less amounts due within one year ​ (3,631) ​ (39) ​ (3,592) Total long-term debt ​ $ 82,166 ​ $ 78 ​ $ 82,088 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2021 ​ ​ ​ Unamortized Debt Balance, Net of ​ ​ Principal Balance ​ Financing Costs ​ Financing Costs NG Advantage debt ​ $ 25,832 ​ ​ 72 ​ ​ 25,760 SG Facility ​ ​ 9,500 ​ ​ — ​ ​ 9,500 Other debt ​ 800 ​ ​ — ​ ​ 800 Total debt ​ 36,132 ​ 72 ​ 36,060 Less amounts due within one year ​ (12,868) ​ ​ (23) ​ ​ (12,845) Total long-term debt ​ $ 23,264 ​ $ 49 ​ $ 23,215
Summary of aggregate maturities of long term debt and capital lease obligations	The following is a summary of the aggregate maturities of debt obligations for each of the annual periods subsequent to December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2022 2023 2024 2025 2026 Thereafter ​ Total NG Advantage debt ​ $ 2,991 ​ $ 8,977 ​ $ 4,161 ​ $ 1,397 ​ $ 8,306 ​ $ — ​ $ 25,832 SG Facility ​ ​ 9,500 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 9,500 Other Debt ​ ​ 377 ​ ​ 262 ​ ​ 161 ​ ​ — ​ ​ — ​ ​ — ​ ​ 800 Total ​ $ 12,868 ​ $ 9,239 ​ $ 4,322 ​ $ 1,397 ​ $ 8,306 ​ $ — ​ $ 36,132

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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 consolidated statements of operations during the periods presented (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2019 2020 2021 Stock-based compensation expense, net of $0 tax in 2019, 2020, and 2021 ​ $ 3,880 ​ $ 2,957 ​ $ 14,994
Summary of the Company's RSU activity	The following table summarizes the Company’s Service-Based RSU activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ Average ​ ​ Number of ​ Fair Value at ​ Shares Grant Date RSU outstanding and unvested as of December 31, 2020 978,716 ​ $ 1.71 Granted 894,344 ​ 10.24 Vested (722,193) ​ 2.54 Forfeited or expired (23,925) ​ 6.86 RSU outstanding and unvested as of December 31, 2021 1,126,942 ​ $ 8.08
Schedule of fair value measurement of warrants	The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2020 and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13 ​ The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ December 31, 2021 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve ​ $1.47 - $1.54 ​ $ 1.50 ​ $ 2.03 - $ 2.15 ​ $ $2.11 Historical Differential to PADD 3 Diesel ​ $0.81 - $1.58 ​ $ 0.99 ​ $ .87 - $ 1.58 ​ $ $1.03 Historical Differential to PADD 5 Diesel ​ $1.66 - $2.58 ​ $ 2.01 ​ $ 1.82 - $ 2.69 ​ $ $2.13
Schedule of warrant activity	The following table summarizes the Amazon Warrant activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ Warrant ​ Shares Outstanding and unvested as of December 31, 2020 — Granted 58,767,714 Vested (14,689,935) Outstanding and unvested as of December 31, 2021 44,077,779
Amazon Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of fair value measurement of warrants	Non-cash stock-based sales incentive contra-revenue charges (“Amazon Warrant Charges”) associated with the Amazon Warrant are recognized as the customer purchases fuel and vesting conditions become probable of being achieved, based on the grant date fair value of the Amazon Warrant. The fair values of the Amazon Warrant were determined as of the grant date in accordance with ASC 718, Compensation – Stock Compensation ​ ​ ​ ​ ​ ​ April 16, 2021 June 14, 2021 Dividend yield 0.0% ​ 0.0% Expected volatility 66.46% ​ 67.97 Risk-free interest rate 1.59% ​ 1.49% Expected term in years 10.0 9.8
Service Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of stock option activity	The following table summarizes the Company’s service-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 8,142,831 ​ $ 5.38 ​ Granted 6,186,260 ​ 8.32 ​ ​ ​ ​ ​ Exercised (1,219,976) ​ 4.59 ​ ​ ​ ​ ​ Forfeited or expired (1,295,444) ​ 8.68 ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 11,813,671 ​ $ 6.64 ​ 7.27 ​ $ 15,409 Options exercisable as of December 31, 2021 5,133,792 ​ $ 5.52 ​ 4.37 ​ $ 12,329 Options vested and expected to vest as of December 31, 2021 11,813,671 ​ $ 6.64 ​ 7.27 ​ $ 15,409
Schedule of assumptions used to estimate the fair value of each award using the Black-Scholes option pricing model	The fair value of each service-based stock option granted was estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ 2019 2020 2021 Dividend yield 0.0% ​ 0.0% ​ 0.0% Expected volatility 57.3% to 61.5% ​ 65.8% to 83.9% ​ 76.8% to 96.8% Risk-free interest rate 2.11% to 2.53% ​ 0.37% to 1.21% ​ 0.58% to 1.31% Expected life in years 6.0 6.0 5.6 to 5.8
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of stock option activity	The following table summarizes the Company’s performance-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 — ​ ​ ​ ​ ​ Granted 1,640,000 ​ 6.77 ​ ​ ​ ​ ​ Exercised — ​ ​ ​ ​ ​ ​ ​ Forfeited or expired — ​ ​ ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 1,640,000 ​ $ 6.77 ​ 9.94 ​ $ — Options exercisable as of December 31, 2021 — ​ $ — ​ — ​ $ —
Schedule of assumptions used to estimate the fair value of each award using the Black-Scholes option pricing model	The fair value of each performance-based stock option granted was estimated as of the date of grant using the Black-Scholes option pricing model and using the following assumptions: ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ 2021 Dividend yield ​ 0.0% Expected volatility ​ 77.1% Risk-free interest rate ​ 1.36% Expected life in years 6.2
Market Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of stock option activity	The following table summarizes the Company’s market-based stock option activity for the year ended December 31, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ Weighted ​ Remaining ​ Aggregate ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ Number of ​ Exercise ​ Term ​ Value ​ Shares Price (in years) (in thousands) Options outstanding as of December 31, 2020 — ​ ​ ​ ​ ​ Granted 3,700,000 ​ 6.77 ​ ​ ​ ​ ​ Exercised — ​ ​ ​ ​ ​ ​ ​ Forfeited or expired — ​ ​ ​ ​ ​ ​ ​ Options outstanding as of December 31, 2021 3,700,000 ​ $ 6.77 ​ 9.94 ​ $ — Options exercisable as of December 31, 2021 — ​ $ — ​ — ​ $ —
Schedule of assumptions used to estimate the fair value of each award using the Black-Scholes option pricing model	The fair value of each market-based stock option granted was estimated on the date of grant using the Monte Carlo simulation model. The Monte Carlo simulation method is subject to variability as certain assumptions must be made, including the derived service period, which is estimated based on likely future stock price performance and volatility of the Company’s common stock price. The fair value of each market-based stock option granted was estimated using the following assumptions:

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of components of income loss before income taxes	The components of income (loss) before income taxes for the years ended December 31, 2019, 2020 and 2021 are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 U.S. ​ $ 14,981 ​ $ (11,216) ​ $ (93,117) Foreign ​ (864) ​ (4) ​ (919) Total income (loss) before income taxes ​ $ 14,117 ​ $ (11,220) ​ $ (94,036)
Schedule of provision for income taxes	The provision for income taxes for the years ended December 31, 2019, 2020 and 2021 consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Current: ​ ​ ​ State ​ $ 116 ​ $ 80 ​ $ 54 Foreign ​ 4 ​ 109 ​ (4) Total current ​ 120 ​ 189 ​ 50 Deferred: ​ ​ ​ Federal ​ 293 ​ 48 ​ 18 State ​ 445 ​ 72 ​ 51 Total deferred ​ 738 ​ 120 ​ 69 Total expense ​ $ 858 ​ $ 309 ​ $ 119
Schedule of reconciliation of federal income tax rate to the actual effective tax rate	Income tax expense (benefit) for the years ended December 31, 2019, 2020 and 2021 computed using the federal income tax rate of 21% as of December 31, 2019, 2020 and 2021 consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Computed expected tax (benefit) ​ $ 2,964 ​ $ (2,356) ​ $ (19,747) Nondeductible expenses ​ 3,087 ​ 2,775 ​ 617 Tax rate differential on foreign earnings ​ 245 ​ (144) ​ 189 Joint ventures ​ 3,745 ​ (5,059) ​ (2) Amazon warrants ​ — ​ ​ — ​ ​ 3,707 Tax credits ​ (10,314) ​ (4,037) ​ (5,299) Other ​ 665 ​ 1,559 ​ 1,463 Change in valuation allowance ​ 466 ​ 7,571 ​ 19,191 Total tax expense ​ $ 858 ​ $ 309 ​ $ 119
Schedule of tax effect of temporary differences that give rise to deferred tax assets and liabilities	The tax effect of temporary differences that give rise to deferred tax assets and liabilities as of December 31, 2020 and 2021 are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 2021 Deferred tax assets: ​ ​ Accrued expenses ​ $ 4,940 ​ $ 5,379 Lease obligations ​ ​ 6,938 ​ ​ 11,388 Alternative minimum tax and general business credits ​ 6,233 ​ 6,787 Stock option expense ​ 6,648 ​ 7,214 Amazon warrants ​ ​ — ​ ​ 16,026 Other ​ 1,545 ​ 3,167 Depreciation and amortization ​ ​ 1,635 ​ ​ 2,582 Loss carryforwards ​ 119,708 ​ 128,514 Total deferred tax assets ​ 147,647 ​ 181,057 Less valuation allowance ​ (134,974) ​ (162,018) Net deferred tax assets ​ 12,673 ​ 19,039 Deferred tax liabilities: ​ ​ Right-of-use assets ​ ​ (6,788) ​ ​ (11,266) Commodity swap contracts ​ (1,596) ​ (649) Goodwill ​ (2,221) ​ (2,534) Investments in joint ventures and partnerships ​ (2,926) ​ (5,517) Total deferred tax liabilities ​ (13,531) ​ (19,966) Net deferred tax liabilities ​ $ (858) ​ $ (927)
Schedule of reconciliation of the total amounts of unrecognized tax benefits	The following is a tabular reconciliation of the total amounts of unrecognized tax benefits for the years ended December 31, 2019, 2020 and 2021 (in thousands): ​ ​ ​ ​ Unrecognized tax benefit—December 31, 2019 $ 41,475 Gross increases—tax positions in current year ​ 2,954 Gross increases—tax positions in prior year ​ ​ 870 Unrecognized tax benefit—December 31, 2020 ​ 45,299 Gross increases—tax positions in current year ​ 3,508 Gross increases—tax positions in prior year ​ ​ 2,142 Gross decreases—tax positions in prior year ​ ​ (364) Unrecognized tax benefit—December 31, 2021 ​ $ 50,585

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases
Schedule of finance and operating lease asset and liability balances	As of December 31, 2020 and 2021, the Company’s finance and operating lease asset and liability balances were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2021 Finance leases: ​ ​ Land, property and equipment, gross ​ $ 4,915 ​ $ 5,617 Accumulated depreciation ​ (1,905) ​ (2,646) Land, property and equipment, net ​ $ 3,010 ​ $ 2,971 ​ ​ ​ ​ ​ ​ ​ Current portion of finance lease obligations ​ $ 840 ​ $ 846 Long-term portion of finance lease obligations ​ 2,552 ​ 2,427 Total finance lease liabilities ​ $ 3,392 ​ $ 3,273 ​ ​ ​ ​ ​ ​ ​ Operating leases: ​ ​ Operating lease right-of-use assets ​ $ 25,967 ​ $ 42,537 ​ ​ ​ ​ ​ ​ ​ Current portion of operating lease obligations ​ $ 2,822 ​ $ 3,551 Long-term portion of operating lease obligations ​ 23,698 ​ 39,431 Total operating lease liabilities ​ $ 26,520 ​ $ 42,982 ​
Schedule of components of lease expense for finance and operating lease liabilities and supplemental information	The components of lease expense for finance and operating leases consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2021 Finance leases: ​ ​ Depreciation on assets under finance leases ​ $ 733 ​ $ 809 Interest on lease liabilities ​ 185 ​ 181 Total finance leases expense ​ $ 918 ​ $ 990 ​ ​ ​ ​ ​ ​ ​ Operating leases: ​ ​ Lease expense ​ $ 6,287 ​ $ 7,313 Lease expense on short-term leases ​ 847 ​ 205 Variable lease expense ​ 2,593 ​ 3,321 Sublease income ​ (736) ​ (726) Total operating leases expense ​ $ 8,991 ​ $ 10,113 ​ Supplemental information on finance and operating leases is as follows (dollars in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2020 ​ 2021 Operating cash outflows from finance leases ​ $ 185 ​ $ 181 Operating cash outflows from operating leases ​ $ 5,503 ​ $ 5,804 Financing cash outflows from finance leases ​ $ 1,242 ​ $ 789 ​ ​ ​ ​ ​ ​ ​ Assets obtained in exchange for new finance lease liabilities (1) ​ $ 1,337 ​ $ 879 ROU assets obtained in exchange for operating lease liabilities (1) ​ $ 96 ​ $ 19,515 ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2021 Weighted-average remaining lease term - finance leases 3.59 years 2.87 years Weighted-average remaining lease term - operating leases 10.81 years 12.31 years ​ ​ ​ ​ ​ Weighted-average discount rate - finance leases 5.27% 5.22% Weighted-average discount rate - operating leases 8.40% 7.55% (1) These amounts are excluded from the accompanying consolidated statements of cash flows as they are non-cash investing, operating and/or financing activities.
Schedule of maturities of operating lease liabilities	The following schedule represents the Company’s maturities of finance and operating lease liabilities as of December 31, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Finance Leases Operating Leases Fiscal year: ​ ​ ​ ​ 2022 ​ $ 990 ​ $ 6,148 2023 ​ 893 ​ 6,037 2024 ​ 1,305 ​ 6,087 2025 ​ 390 ​ 6,028 2026 ​ — ​ 5,840 Thereafter ​ — ​ 38,033 Total minimum lease payments ​ 3,578 ​ 68,173 Less amount representing interest ​ (305) ​ (25,191) Present value of lease liabilities ​ $ 3,273 ​ $ 42,982
Schedule of maturities of finance lease liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ Finance Leases Operating Leases Fiscal year: ​ ​ ​ ​ 2022 ​ $ 990 ​ $ 6,148 2023 ​ 893 ​ 6,037 2024 ​ 1,305 ​ 6,087 2025 ​ 390 ​ 6,028 2026 ​ — ​ 5,840 Thereafter ​ — ​ 38,033 Total minimum lease payments ​ 3,578 ​ 68,173 Less amount representing interest ​ (305) ​ (25,191) Present value of lease liabilities ​ $ 3,273 ​ $ 42,982
Schedule of maturities of lease receivables	The following schedule represents the Company’s maturities of lease receivables as of December 31, 2021 (in thousands): ​ ​ ​ ​ ​ Fiscal year: ​ 2022 ​ $ 1,182 2023 ​ 962 2024 ​ 962 2025 ​ 962 2026 ​ 1,034 Thereafter ​ 2,339 Total minimum lease payments ​ 7,441 Less amount representing interest ​ (1,908) Present value of lease receivables ​ $ 5,533

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
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 per share for the years ended December 31, 2019, 2020 and 2021 (in thousands, except share and per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Net income (loss) attributable to Clean Energy Fuels Corp. $ 20,421 $ (9,864) $ (93,146) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ ​ 204,573,287 ​ ​ 200,657,912 ​ ​ 213,118,694 Dilutive effect of potential common shares from restricted stock units, stock options and stock warrants ​ ​ 1,414,222 ​ ​ — ​ ​ — Weighted-average common shares outstanding - diluted ​ ​ 205,987,509 ​ ​ 200,657,912 ​ ​ 213,118,694 Basic income (loss) per share ​ $ 0.10 ​ $ (0.05) ​ $ (0.44) Diluted income (loss) per share ​ $ 0.10 ​ $ (0.05) ​ $ (0.44)
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. ​ ​ ​ ​ ​ ​ ​ (in shares) 2019 2020 2021 Stock options 7,652,463 8,142,831 17,153,671 Convertibles notes 3,164,557 1,112,783 — Restricted stock units — 978,716 ​ 1,126,942 Amazon warrant shares ​ — ​ — ​ 58,767,714 Total ​ 10,817,020 ​ 10,234,330 ​ 77,048,327

Reportable Segments and Geogr_2

Reportable Segments and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Schedule of revenue, operating income (loss), and long-lived assets shown for each geographic area	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 2020 2021 Revenue: ​ ​ ​ United States ​ $ 338,549 ​ $ 281,546 ​ $ 252,310 Canada ​ 5,516 ​ 10,178 ​ 3,336 Total revenue ​ $ 344,065 ​ $ 291,724 ​ $ 255,646 Operating income (loss): ​ ​ ​ United States ​ $ 10,805 ​ $ (9,853) ​ $ (94,157) Canada ​ (877) ​ 9 ​ (891) Total operating income (loss) ​ $ 9,928 ​ $ (9,844) ​ $ (95,048) Long-lived assets: ​ ​ ​ United States ​ $ 415,548 ​ $ 383,463 ​ $ 440,770 Canada ​ 226 ​ 202 ​ 630 Total long-lived assets ​ $ 415,774 ​ $ 383,665 ​ $ 441,400

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Inventories
Raw materials and spare parts	$ 31,302	$ 28,100
Total inventory	$ 31,302	$ 28,100

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Proceeds from grants	$ 0.5	$ 0	$ 1.6
LNG liquefaction plants | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
LNG liquefaction plants | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years
Station equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Trailers | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Other equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Other equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Long-Lived Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill and intangible assets
Long-lived intangible impairment	$ 0	$ 0	$ 0
Total intangible assets	18,820	13,320
Less accumulated amortization	(13,320)	(12,856)
Net intangible assets	5,500	464
Amortization expense	500	800	$ 1,000
Estimated amortization expense
2022	0
2023	0
2024	300
2025	300
2026	300
Thereafter	4,600
Customer relationships
Goodwill and intangible assets
Total intangible assets	$ 5,376	5,376
Customer relationships | Minimum
Goodwill and intangible assets
Estimated useful lives	1 year
Customer relationships | Maximum
Goodwill and intangible assets
Estimated useful lives	8 years
Acquired contracts
Goodwill and intangible assets
Total intangible assets	$ 9,884	4,384
Acquired contracts | Minimum
Goodwill and intangible assets
Estimated useful lives	1 year
Acquired contracts | Maximum
Goodwill and intangible assets
Estimated useful lives	20 years
Contractual Rights to Manure Feedstock
Goodwill and intangible assets
Estimated useful lives	20 years
Contractual rights acquired	$ 5,500
Cash paid for Acquired contracts	1,000
Acquired contracts included in Accrued liabilities	$ 4,500
Initial term of contractual rights acquired	20 years
Trademark and trade names
Goodwill and intangible assets
Total intangible assets	$ 2,700	2,700
Trademark and trade names | Minimum
Goodwill and intangible assets
Estimated useful lives	2 years
Trademark and trade names | Maximum
Goodwill and intangible assets
Estimated useful lives	10 years
Non-compete agreements
Goodwill and intangible assets
Estimated useful lives	3 years
Total intangible assets	$ 860	$ 860

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Goodwill	$ 64,328	$ 64,328	$ 64,328

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Commodity Swap and Customer Contract
Total gain (loss)	$ (3.5)	$ 2.1	$ (6.6)

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Alternative Fuels Tax Credit (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021$ / gal	Dec. 31, 2020$ / gal	Dec. 31, 2019USD ($)$ / gal
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Federal alternative fuels tax credit - credits recognized as revenue | $			$ 47.1
Federal fuel tax credit - CNG (in dollars per gasoline gallon equivalent)	0.50	0.50	0.50
Federal fuel tax credit - LNG (in dollars per liquid gallon)	0.50	0.50	0.50

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Advertising expense	$ 0	$ 0	$ 1.2

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Foreign Currency Translation and Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Foreign exchange transactions gains (losses) included in other income (expense)	$ 0	$ 0	$ 0

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contracts with Customers
Revenue	$ 255,646	$ 291,724	$ 344,065
Contra revenue charge	83,641	0	0
Volume -Related
Revenue from Contracts with Customers
Revenue	218,540	245,300	273,535
Gain (Loss) changes in fair value	(3,500)	2,100	(6,600)
Station construction sales
Revenue from Contracts with Customers
Revenue	16,406	26,593	23,120
AFTC
Revenue from Contracts with Customers
Revenue	$ 20,700	$ 19,831	47,123
Other
Revenue from Contracts with Customers
Revenue			$ 287

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Remaining Performance Obligations (Details) $ in Millions	Dec. 31, 2021USD ($)
Remaining Performance Obligations
Revenue, remaining performance obligation, amount	$ 19.8
Minimum
Remaining Performance Obligations
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months
Maximum
Remaining Performance Obligations
Revenue, remaining performance obligation, expected timing of satisfaction, period	24 months

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Costs to Fulfill a Contract (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Capitalized contract cost, gross	$ 10.1	$ 10.4
Capitalized contract cost, accumulated depreciation	7.6	7.1
Capitalized contract cost, amortization	$ 0.5	$ 0.8

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Accounts receivable, net	$ 87,433	$ 61,784
Contract Assets - Current	966	729
Contract Assets - Noncurrent	3,532	3,998
Contract Assets - Total	4,498	4,727
Contract Liabilities - Current	5,523	1,638
Contract Liabilities - Noncurrent		59
Contract Liabilities - Total	$ 5,523	$ 1,697

Revenue from Contracts with C_7

Revenue from Contracts with Customers - Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue from Contracts with Customers
Contract Liabilities - Current	$ 5,523	$ 1,638
Revenue recognized during period	1,500	4,800
Station construction sales
Revenue from Contracts with Customers
Contract Liabilities - Current	5,400	1,000
Volume -Related
Revenue from Contracts with Customers
Contract Liabilities - Current	$ 100	$ 600

Divestitures - BP Transaction (

Divestitures - BP Transaction (Details) $ in Thousands	Mar. 01, 2019USD ($)	Feb. 27, 2017USD ($)facility	Dec. 31, 2019USD ($)	Feb. 28, 2018USD ($)shares	Dec. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Acquisition and Divestitures
Asset purchase agreement, gain from sale of certain assets of subsidiary					$ 3,885	$ 1,063	$ 7,455
Goodwill			$ 64,328		64,328	64,328	64,328
BP Products North America, Inc.
Acquisition and Divestitures
Production facilities to be developed | facility		2
Asset purchase agreement, cash paid	$ 5,400			$ 900
Asset purchase agreement, accrued amount			900		500	100	900
Asset purchase agreement, gain from sale of certain assets of subsidiary			8,400		4,400	1,000
Asset purchase agreement, contingent consideration (up to)		$ 25,000			3,900	$ 1,100	7,500
Asset purchase agreement, contingent consideration, term		5 years
Asset purchase agreement, payment of transaction costs			$ 2,800	$ 100	$ 10,300		$ 600
Asset purchase agreement, shares issued (in shares) | shares				15,877	770,269
Asset purchase agreement, shares issued, value				$ 0	$ 2,000
Maximum | BP Products North America, Inc.
Acquisition and Divestitures
Asset purchase agreement, contingent consideration, term			5 years
Minimum | BP Products North America, Inc.
Acquisition and Divestitures
Asset purchase agreement, contingent consideration, term			4 years

Divestitures - SAFE&CEC S.r.l.

Divestitures - SAFE&CEC S.r.l. (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 29, 2017
Acquisition and Divestitures
Gain from sale of certain assets of subsidiary	$ 3,885	$ 1,063	$ 7,455
Working capital adjustments, funding for certain post-closing commitments, and transaction fees	12,914	8,748
Loss before income taxes	94,036	11,220	(14,117)
Gain from formation of equity method investment		700
Income (loss) from equity method investments	$ (430)	(161)	(119)
SAFE&CEC S.r.l.
Acquisition and Divestitures
Ownership interest (as a percent)	49.00%			49.00%
Income (loss) from equity method investments	$ 600	(200)	$ 0
Investment balance	$ 23,900	$ 24,700
SAFE&CEC S.r.l. | Landi Renzo S.p.A.
Acquisition and Divestitures
Ownership interest (as a percent)				51.00%

Investments in Other Entities_3

Investments in Other Entities and Noncontrolling Interest in a Subsidiary - Total Joint Venture (Details) - USD ($) $ in Thousands	Nov. 01, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 12, 2021	Mar. 12, 2021	Mar. 03, 2021	Jan. 02, 2019
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments		$ (430)	$ (161)	$ (119)
Summarized Financial Information
Net loss		(94,155)	(11,529)	$ 13,259
Current assets		409,936	263,039
Total assets		957,070	715,027
Current liabilities		125,904	79,843
Total liabilities		201,659	$ 192,177
Socit Gnrale | Term Loan Facility
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity (up to)								$ 100,000
ADG RNG Production Facilities | Socit Gnrale | Term Loan Facility
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity (up to)						$ 20,000	$ 20,000
TotalEnergies
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments		(100)
Investment balance		4,700
Summarized Financial Information
Operating income (loss)		(119)
Net loss		(119)
Current assets		3,086
Non-current assets		13,103
Total assets		16,189
Current liabilities		6,770
Total liabilities		$ 6,770
TotalEnergies | ADG RNG Production Facilities
Schedule of Equity Method Investments [Line Items]
Investment commitment of equity in production projects							400,000
Investment commitment in joint venture							50,000
TotalEnergies | ADG RNG Production Facilities | TotalEnergies S.E.
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture							$ 50,000
TotalEnergies | DR Development Agreement
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture					$ 7,000
Initial contribution commitment	$ 4,800
TotalEnergies | DR Development Agreement | TotalEnergies S.E.
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture					$ 7,000
Initial contribution commitment	$ 4,800

Investments in Other Entities_4

Investments in Other Entities and Noncontrolling Interest in a Subsidiary - bp Joint Venture (Details) - USD ($) $ in Thousands, shares in Millions	Jun. 21, 2021	Apr. 13, 2021	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2022	Dec. 18, 2020	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments				$ (430)	$ (161)	$ (119)
Summarized Financial Information
Net loss				(94,155)	(11,529)	13,259
Net income (loss)				(93,146)	(9,864)	20,421
Current assets			$ 409,936	409,936	263,039
Total assets			957,070	957,070	715,027
Current liabilities			125,904	125,904	79,843
Total liabilities			201,659	201,659	192,177
Equity attributable to shareholders			747,076	747,076	513,506
Equity attributable to noncontrolling interest			8,335	8,335	9,344
Total equity			755,411	755,411	$ 522,850	$ 543,029			$ 525,009
BP Products North America | bp Loan
Schedule of Equity Method Investments [Line Items]
Debt issuance amount								$ 50,000
bpJV
Summarized Financial Information
Operating income (loss)				(678)
Net loss				(603)
Net income (loss)				(599)
Current assets			152,072	152,072
Non-current assets			70,433	70,433
Total assets			222,505	222,505
Current liabilities			24,932	24,932
Non-current liabilities			1,000	1,000
Total liabilities			25,932	25,932
Equity attributable to shareholders			191,170	191,170
Equity attributable to noncontrolling interest			5,403	5,403
Total equity			$ 196,573	$ 196,573
bpJV | ADG RNG Production Facilities
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture	$ 50,200	$ 30,000
Additional commitment in joint venture		20,000
Initial contribution commitment		$ 30,000
Ownership interest (as a percent)			50.00%	50.00%
Income (loss) from equity method investments				$ (400)
Investment balance			$ 69,800	69,800
bpJV | ADG RNG Production Facilities | Capital Contribution
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture			71,600	71,600
Initial contribution commitment			20,000
Capital call contribution amount			$ 143,200	$ 143,200
bpJV | ADG RNG Production Facilities | Capital Contribution | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture							$ 51,600
bpJV | ADG RNG Production Facilities | Class A Units
Schedule of Equity Method Investments [Line Items]
Number of units received		30
Payments to acquire units in joint venture	20,000
Priority Return to acquire additional units	$ 200
bpJV | ADG RNG Production Facilities | bp
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture		$ 50,000
Ownership interest (as a percent)			50.00%	50.00%
bpJV | ADG RNG Production Facilities | bp | Capital Contribution
Schedule of Equity Method Investments [Line Items]
Investment commitment in joint venture			$ 71,600	$ 71,600
Initial contribution commitment			$ 71,600
bpJV | ADG RNG Production Facilities | bp | Class A Units
Schedule of Equity Method Investments [Line Items]
Number of units received		30
bpJV | ADG RNG Production Facilities | bp | Class B Units
Schedule of Equity Method Investments [Line Items]
Number of units received		20

Investments in Other Entities_5

Investments in Other Entities and Noncontrolling Interest in a Subsidiary - SAFE&CEC S.r.l (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 29, 2017
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ (430)	$ (161)	$ (119)
Summarized Financial Information
Net income (loss)	(94,155)	(11,529)	13,259
Current assets	409,936	263,039
Total assets	957,070	715,027
Current liabilities	125,904	79,843
Total liabilities	$ 201,659	192,177
SAFE&CEC S.r.l.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	49.00%			49.00%
Income (loss) from equity method investments	$ 600	(200)	0
Investment balance	23,900	24,700
Summarized Financial Information
Revenue	109,119	89,535	80,886
Gross profit	25,784	19,008	20,525
Operating income (loss)	4,728	609	1,207
Net income (loss)	2,392	(306)	$ 93
Current assets	75,137	60,406
Non-current assets	56,052	58,140
Total assets	131,189	118,546
Current liabilities	58,910	55,780
Non-current liabilities	21,730	11,808
Total liabilities	$ 80,640	$ 67,588

Investments in Other Entities_6

Investments in Other Entities and Noncontrolling Interest in a Subsidiary - Other Equity Method Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Income (loss) from equity method investments	$ (430)	$ (161)	$ (119)
Summarized Financial Information
Net loss	(94,155)	(11,529)	13,259
Current assets	409,936	263,039
Total assets	957,070	715,027
Current liabilities	125,904	79,843
Total liabilities	201,659	192,177
Other Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Investment balance	3,500	2,300
Income (loss) from equity method investments	(600)	100	(100)
Summarized Financial Information
Revenue	704	463	546
Gross profit	216	155	178
Operating income (loss)	(1,757)	(90)	(214)
Net loss	(1,793)	(126)	$ (250)
Current assets	1,349	1,233
Non-current assets	7,047	5,553
Total assets	8,396	6,786
Current liabilities	1,012	1,421
Non-current liabilities	192	66
Total liabilities	$ 1,204	$ 1,487

Investments in Other Entities_7

Investments in Other Entities and Noncontrolling Interest in a Subsidiary - NG Advantage (Details) - USD ($) $ in Thousands	Feb. 29, 2020	Feb. 06, 2020	Oct. 01, 2018	Feb. 28, 2018	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Feb. 28, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 24, 2020	Oct. 14, 2014
Business Acquisition [Line Items]
Payments to acquire additional controlling interest										$ 78,919	$ 650
Proceeds from debt instruments										4,400	65,860	$ 15,294
Outstanding balance										36,060	85,680
Income (loss) attributable to noncontrolling interest										(1,009)	(1,665)	(7,162)
Investments Carried at Cost
Investments carried at cost										8,000
NG Advantage
Business Acquisition [Line Items]
Ownership interest before transaction (as a percent)				53.30%
Ownership interest after transaction (as a percent)				53.50%
Income (loss) attributable to noncontrolling interest										(1,000)	(1,700)	(7,200)
Noncontrolling interest, fair value										8,300	$ 9,300
BP Products North America | NG Advantage | Long-Term Natural Gas Purchase Contracts
Business Acquisition [Line Items]
Contingent consideration, liability (up to)				$ 30,000									$ 15,000
NG Advantage
Business Acquisition [Line Items]
Purchase of interest by parent, shares purchased (in shares)			1,000,001
Payments to acquire additional controlling interest			$ 5,000
Ownership interest before transaction (as a percent)		64.60%	53.50%
Ownership interest after transaction (as a percent)		93.20%	61.70%						64.60%		93.30%
Debt Instrument, Face Amount										5,000
NG Advantage | November 2019 Convertible Note
Business Acquisition [Line Items]
Debt Instrument, Face Amount												$ 26,700
Number of common units to be called by warrants (in shares)												2,086,879
NG Advantage | Payment Obligations
Business Acquisition [Line Items]
Purchase of interest by parent, shares purchased (in shares)				19,660	100,000	100,000	100,000	100,000	400,000
NG Advantage | Common unit purchase agreement
Business Acquisition [Line Items]
Ownership interest acquired														53.30%
Issuance of equity by subsidiary to parent (in shares)	283,019
NG Advantage | Clean Energy Fuels Corp | Convertible Debt
Business Acquisition [Line Items]
Outstanding balance										$ 18,400

Cash, Cash Equivalents and Rest

Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash
Cash and cash equivalents	$ 99,448	$ 108,977
Total cash and cash equivalents	99,448	108,977
Total restricted cash	7,008	11,000
Total cash, cash equivalents and restricted cash	106,456	119,977	$ 53,222	$ 34,624
Amount in excess of FDIC and CDIC limits	98,000	107,600
Standby letters of credit
Restricted Cash
Total restricted cash		4,000
Held as collateral
Restricted Cash
Restricted cash	$ 7,008	$ 7,000

Short-Term Investments (Details

Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 129,741	$ 29,528
Gross Unrealized gain (Loss)	(19)
Estimated Fair Value	129,722	29,528
Municipal bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,001	28,998
Gross Unrealized gain (Loss)	(1)
Estimated Fair Value	6,000	28,998
Zero coupon bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	123,210
Gross Unrealized gain (Loss)	(18)
Estimated Fair Value	123,192
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	530	530
Estimated Fair Value	$ 530	$ 530

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	12 Months Ended
	Oct. 31, 2018contractgal	Dec. 31, 2021$ / galgal	Dec. 31, 2020$ / galgal
Derivative [Line Items]
Derivative asset, number of instruments held | contract	2
Volumes (Diesel Gallons) | gal	5	11.9	16.9
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	Dec. 31, 2021	Dec. 31, 2020
Derivative Assets
Gross Amounts Recognized	$ 6,776	$ 6,439
Net Amount Presented	6,776	6,439
Derivative Liability
Gross Amounts Recognized	4,383	556
Net Amount Presented	4,383	556
Current portion of derivative assets, related party | Commodity swaps
Derivative Assets
Gross Amounts Recognized		1,591
Net Amount Presented		1,591
Current portion of derivative liabilities, related party | Commodity swaps
Derivative Liability
Gross Amounts Recognized	1,900
Net Amount Presented	1,900
Long-term portion of derivative assets, related party | Commodity swaps
Derivative Assets
Gross Amounts Recognized		4,057
Net Amount Presented		4,057
Long-term portion of derivative liabilities, related party | Commodity swaps
Derivative Liability
Gross Amounts Recognized	2,483
Net Amount Presented	2,483
Prepaid expenses and other current assets | Fueling agreements
Derivative Assets
Gross Amounts Recognized	2,038	249
Net Amount Presented	2,038	249
Notes receivable and other long-term assets, net | Fueling agreements
Derivative Assets
Gross Amounts Recognized	4,738	542
Net Amount Presented	$ 4,738	542
Accrued liabilities | Fueling agreements
Derivative Liability
Gross Amounts Recognized		283
Net Amount Presented		283
Other long-term liabilities | Fueling agreements
Derivative Liability
Gross Amounts Recognized		273
Net Amount Presented		$ 273

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities - Schedule of Weighted-Average Price of Open Commodity Swap Contracts (Details) - Not Designated as Hedging Instrument	12 Months Ended
	Dec. 31, 2021$ / galgal	Dec. 31, 2020$ / galgal
Commodity Swap 2021
Derivative [Line Items]
Volumes (Diesel Gallons) | gal		5,000,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal		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 - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Commodity swaps | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.03	1.47
Commodity swaps | Minimum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.87	0.81
Commodity swaps | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.82	1.66
Commodity swaps | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.15	1.54
Commodity swaps | Maximum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.58	1.58
Commodity swaps | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.69	2.58
Commodity swaps | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.11	1.50
Commodity swaps | Weighted Average | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.03	0.99
Commodity swaps | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.13	2.01
Fueling agreements | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.03	1.47
Fueling agreements | Minimum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.87	0.81
Fueling agreements | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.82	1.66
Fueling agreements | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.15	1.54
Fueling agreements | Maximum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.58	1.58
Fueling agreements | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.69	2.58
Fueling agreements | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.11	1.50
Fueling agreements | Weighted Average | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.03	0.99
Fueling agreements | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.13	2.01

Fair Value Measurements - Trans

Fair Value Measurements - Transfers (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
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

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Available-for-sale securities	$ 129,722	$ 29,528
Short-term investments	129,722	29,528
Municipal bonds and notes
Assets:
Available-for-sale securities	6,000	28,998
Zero coupon bonds
Assets:
Available-for-sale securities	123,192
Certificates of deposit
Assets:
Available-for-sale securities	530	530
Fair value measured on recurring basis | Municipal bonds and notes
Assets:
Available-for-sale securities	6,000	28,998
Fair value measured on recurring basis | Zero coupon bonds
Assets:
Available-for-sale securities	123,192
Fair value measured on recurring basis | Certificates of deposit
Assets:
Short-term investments	530	530
Fair value measured on recurring basis | Commodity swap contracts
Assets:
Derivative assets		5,648
Liabilities:
Derivative liabilities	4,383
Fair value measured on recurring basis | Embedded derivatives
Assets:
Derivative assets	6,776	791
Liabilities:
Derivative liabilities		556
Fair value measured on recurring basis | Level 2 | Municipal bonds and notes
Assets:
Available-for-sale securities	6,000	28,998
Fair value measured on recurring basis | Level 2 | Zero coupon bonds
Assets:
Available-for-sale securities	123,192
Fair value measured on recurring basis | Level 2 | Certificates of deposit
Assets:
Short-term investments	530	530
Fair value measured on recurring basis | Level 3 | Commodity swap contracts
Assets:
Derivative assets		5,648
Liabilities:
Derivative liabilities	4,383
Fair value measured on recurring basis | Level 3 | Embedded derivatives
Assets:
Derivative assets	$ 6,776	791
Liabilities:
Derivative liabilities		$ 556

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Recognition - Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
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
Commodity swap contracts
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	$ 5,648	$ 3,270
Settlements, net	(225)	(1,652)
Total gain (loss)	5,423	(4,030)
Ending balance		5,648
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(5,648)	2,378
Embedded derivatives
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	791	723
Total gain (loss)	5,985	68
Ending balance	6,776	791
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 5,985	$ 68

Fair Value Measurements - Fai_2

Fair Value Measurements - Fair Value Recognition - Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
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
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	$ 1,083	56
Total gain (loss)	(5,466)	108
Ending Balance	(4,383)
Change in unrealized gain (loss) included in earnings	(4,383)	164
Embedded derivatives
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance	(556)	(81)
Total gain (loss)	556	(475)
Ending Balance		(556)
Change in unrealized gain (loss) included in earnings	$ 556	(475)
Amazon warrant shares
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance		40
Total gain (loss)		40
Change in unrealized gain (loss) included in earnings		$ 40

Other Receivables (Details)

Other Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Other Receivables
Other receivables	$ 24,447	$ 23,655
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	419	394
Accrued customer billings
Other Receivables
Other receivables	4,417	6,335
Fuel tax credits
Other Receivables
Other receivables	12,684	10,556
Other receivables
Other Receivables
Other receivables	$ 6,927	$ 6,370

Land, Property and Equipment (D

Land, Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Land, Property and Equipment
Land, property and equipment, gross	$ 693,689	$ 685,356
Less accumulated depreciation	(431,928)	(394,445)
Total land, property and equipment, net	261,761	290,911
Capitalized software costs, net	33,800	32,300
Accumulated amortization on the capitalized software costs	30,400	28,800
Amortization expense related to the capitalized software costs	1,600	2,500	$ 3,900
Amount included in accounts payable balances	2,100	1,700
Land
Land, Property and Equipment
Land, property and equipment, gross	3,476	3,476
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,633	94,633
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	354,699	344,839
Trailers
Land, Property and Equipment
Land, property and equipment, gross	72,783	79,860
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	93,135	89,276
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 74,963	$ 73,272

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 28,106	$ 18,175
Accrued employee benefits	4,547	4,282
Accrued gas and equipment purchases	17,158	9,897
Accrued interest	893	512
Accrued property and other taxes	3,369	3,094
Accrued salaries and wages	8,172	7,646
Embedded derivatives		283
Other	12,914	8,748
Total accrued liabilities	$ 75,159	$ 52,637

Debt - Debt Obligations (Detail

Debt - Debt Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Principal Balance
Total debt	$ 36,132	$ 85,797
Less amounts due within one year	(12,868)	(3,631)
Total long-term debt	23,264	82,166
Unamortized Debt Financing Costs
Total debt	72	117
Less amounts due within one year	(23)	(39)
Total long-term debt	49	78
Balance, Net of Financing Costs
Total debt	36,060	85,680
Less amounts due within one year	(12,845)	(3,592)
Total long-term debt	23,215	82,088
bp Loan
Principal Balance
Total debt		50,000
Balance, Net of Financing Costs
Total debt		50,000
NG Advantage debt
Principal Balance
Total debt	25,832	29,535
Unamortized Debt Financing Costs
Total debt	72	117
Balance, Net of Financing Costs
Total debt	25,760	29,418
Term Loan Facility
Principal Balance
Total debt	9,500	5,100
Balance, Net of Financing Costs
Total debt	9,500	5,100
Other debt
Principal Balance
Total debt	800	1,162
Balance, Net of Financing Costs
Total debt	$ 800	$ 1,162

Debt - Aggregate Maturities (De

Debt - Aggregate Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Summary of aggregate maturities of debt obligations
2022	$ 12,868
2023	9,239
2024	4,322
2025	1,397
2026	8,306
Total debt	36,132	$ 85,797
bp Loan
Summary of aggregate maturities of debt obligations
Total debt		50,000
NG Advantage debt
Summary of aggregate maturities of debt obligations
2022	2,991
2023	8,977
2024	4,161
2025	1,397
2026	8,306
Total debt	25,832	29,535
Term Loan Facility
Summary of aggregate maturities of debt obligations
2022	9,500
Total debt	9,500	5,100
Other debt
Summary of aggregate maturities of debt obligations
2022	377
2023	262
2024	161
Total debt	$ 800	$ 1,162

Debt - SG Credit and TOTAL Cred

Debt - SG Credit and TOTAL Credit Support Agreement (Details) - USD ($) $ in Thousands	Jan. 02, 2019	Dec. 31, 2021	Mar. 12, 2021	Mar. 03, 2021	Dec. 31, 2020
Long-term debt [Line Items]
Outstanding amount		$ 36,132			$ 85,797
Proceeds from revolving line of credit		1,450
Term Loan Facility
Long-term debt [Line Items]
Outstanding amount		9,500			$ 5,100
Term Loan Facility | Socit Gnrale
Long-term debt [Line Items]
Maximum borrowing capacity (up to)	$ 100,000
Commitment fee percentage	0.39%
Quarterly principal payments		2,500
Covenant for debt default	$ 20,000
Outstanding amount		$ 9,500
Term Loan Facility | Socit Gnrale | London Interbank Offered Rate (LIBOR)
Long-term debt [Line Items]
Basis spread on variable rate	1.30%
Term Loan Facility | Socit Gnrale | Station Build Costs
Long-term debt [Line Items]
Maximum borrowing capacity (up to)			$ 45,000
Term Loan Facility | Socit Gnrale | ADG RNG Production Facilities
Long-term debt [Line Items]
Maximum borrowing capacity (up to)			$ 20,000	$ 20,000
Term Loan 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
Term Loan 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 Thousands	Feb. 01, 2021USD ($)	Dec. 10, 2020USD ($)	Dec. 20, 2018USD ($)	Mar. 01, 2018USD ($)installment	Dec. 18, 2017USD ($)installment	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Nov. 30, 2016USD ($)installment
Long-term debt [Line Items]
Loss on extinguishment of debt						$ 39	$ 1,249
Proceeds from revolving line of credit						1,450
Repayments of borrowing under revolving line of credit						1,450
Compression Station
Long-term debt [Line Items]
Purchase price			$ 7,000
Sale leaseback transaction, term			5 years
Annual rate (as a percent)			12.00%
Monthly rental payments			$ 100
BoA | BoA MLA
Long-term debt [Line Items]
Proceeds from sale of equipment in sale-leaseback agreement					$ 2,100
Sale leaseback transaction, term					5 years
Number of equal monthly installments | installment					60
Annual rate (as a percent)					4.86%
First National | First National MLA
Long-term debt [Line Items]
Proceeds from sale of equipment in sale-leaseback agreement				$ 6,300
Sale leaseback transaction, term				6 years
Number of equal monthly installments | installment				72
First National | Nations MLA
Long-term debt [Line Items]
Annual rate (as a percent)				9.28%
NG Advantage debt | Long-term portion of restricted cash | Berkshire Bank
Long-term debt [Line Items]
Loan pledged as collateral						7,000
NG Advantage debt | 5% maturing on January 1, 2026 | Berkshire Bank
Long-term debt [Line Items]
Debt issuance amount	$ 14,500
Interest rate	5.00%
Period during which the debt instrument principal balance is required to be paid following its issuance	5 years
NG Advantage debt | Revolving line of credit | Berkshire Bank
Long-term debt [Line Items]
Maximum borrowing capacity (up to)		$ 1,000
Outstanding line of credit						$ 0
Interest rate during period (as a percent)		3.00%
NG Advantage debt | Revolving line of credit | Berkshire Bank | Prime Rate
Long-term debt [Line Items]
Basis spread on variable rate		0.25%
NG Advantage debt | 5.17% Term Loan | Wintrust Commercial Finance
Long-term debt [Line Items]
Debt issuance amount								$ 4,700
Number of monthly installments | installment								72
Interest rate								5.17%

Debt - BP Loan and Plains Credi

Debt - BP Loan and Plains Credit Facility (Details) - USD ($) $ in Millions	Dec. 18, 2020	Dec. 31, 2021	Sep. 16, 2021	May 01, 2021
bp Loan | BP Products North America
Debt Instrument [Line Items]
Debt issuance amount	$ 50
bp Loan | BP Products North America | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	4.33%
Revolving line of credit | Plains Credit Facility | Plains
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)			$ 20	$ 20
Outstanding line of credit		$ 0
Remaining borrowing capacity			18
Revolving line of credit | Plains Credit Facility | Minimum | Plains
Debt Instrument [Line Items]
Interest rate (as a percent)				3.25%
Standby letters of credit | Plains Credit Facility | Plains
Debt Instrument [Line Items]
Maximum borrowing capacity (up to)			$ 2
Outstanding line of credit		$ 0

Debt - Other Debt (Details)

Debt - Other Debt (Details) - Other debt	Dec. 31, 2021	Dec. 31, 2020
Long-term debt [Line Items]
Weighted average interest rate	4.34%	4.38%
Maximum
Long-term debt [Line Items]
Interest rate	4.75%	4.75%

Stockholders' Equity - Authoriz

Stockholders' Equity - Authorized Shares (Details)	Dec. 31, 2021class$ / sharesshares	Jun. 14, 2021shares	Jun. 13, 2021shares	Dec. 31, 2020$ / sharesshares
Stockholders' Equity Note [Abstract]
Authorized number of classes of capital stock | class	2
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001			$ 0.0001
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.0001			$ 0.0001
Authorized shares (in shares)	455,000,000
Common stock, authorized (in shares)	454,000,000	454,000,000	304,000,000	304,000,000
Preferred stock, authorized (in shares)	1,000,000			1,000,000

Stockholders' Equity - Voting R

Stockholders' Equity - Voting Rights (Details)	Dec. 31, 2021Vote
Equity [Abstract]
Number of votes per share held by holders of common stock	1

Stockholders' Equity - Total Pr

Stockholders' Equity - Total Private Placement (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 13, 2018	May 09, 2018	Dec. 31, 2021
Stockholders' equity
Fees and issuance costs			$ 6,534
Purchase Agreement
Stockholders' equity
Number of shares issued in transaction (in shares)	50,856,296	50,856,296
Price per share (in dollars per share)		$ 1.64
Percentage of ownership after transaction	25.00%
Consideration received on transaction	$ 83,400
Fees and issuance costs	$ 1,900
Purchase Agreement | Purchase Percentage Covenant, Threshold
Stockholders' equity
Percentage of ownership after transaction		5.00%
Purchase Agreement | Purchase Percentage Covenant, Maximum
Stockholders' equity
Percentage of ownership after transaction		30.00%

Stockholders' Equity - At the M

Stockholders' Equity - At the Market Offering (Details) - USD ($) $ in Thousands	Jun. 08, 2021	Jun. 03, 2021	Dec. 31, 2021	Jun. 07, 2021	May 10, 2021
ATM Program Activity
Fees and issuance costs			$ 6,534
At The Market Offering
ATM Program Activity
Fees and issuance costs			6,500
Goldman Sachs & Co. LLC | At The Market Offering
ATM Program Activity
Aggregate offering price				$ 100,000	$ 100,000
Gross proceeds			$ 200,000
Shares issued (in shares)	10,473,946	12,362,237	22,836,183
Fees and issuance costs			$ 6,000

Stockholders' Equity - Share Re

Stockholders' Equity - Share Repurchase program (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 07, 2021	Mar. 12, 2020
Stockholders' Equity Note [Abstract]
Approved share repurchase program			$ 50,000	$ 30,000
Repurchase of common stock (in shares)	452,700
Cost to repurchase common stock	$ 2,916	$ 14,647
Amount utilized under the repurchase plan	$ 17,400
Stock Repurchase Program Total Stock Repurchased	8,197,086

Stockholders' Equity - Stock Ba

Stockholders' Equity - Stock Based Compensation (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Stock-based compensation expense, net of $0 tax in 2019, 2020, and 2021		$ 14,994	$ 2,957	$ 3,880
Stock-based compensation expense, tax		$ 0	$ 0	$ 0
Amended 2016 Plan
Stock-based compensation
Increase in the aggregate number of shares	17,500,000
Number of shares available for future grant		7,595,607

Stockholders' Equity - Service-

Stockholders' Equity - Service-Based Stock Options (Details) - Service Based Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Vesting period	3 years
Contractual term	10 years
Number of Shares
Outstanding at the beginning of the period (in shares)	8,142,831
Granted (in shares)	6,186,260
Exercised (in shares)	(1,219,976)
Forfeited or expired (in shares)	(1,295,444)
Outstanding at the end of the period (in shares)	11,813,671	8,142,831
Exercisable at the end of the period (in shares)	5,133,792
Vested and expected to vest at the end of the period (in shares)	11,813,671
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 5.38
Granted (in dollars per share)	8.32
Exercised (in dollars per share)	4.59
Forfeited or expired (in dollars per share)	8.68
Outstanding at the end of the period (in dollars per share)	6.64	$ 5.38
Exercisable at the end of the period (in dollars per share)	5.52
Vested and expected to vest at the end of the period (in dollars per share)	$ 6.64
Additional option disclosures
Outstanding at the end of the period, weighted average remaining contractual term	7 years 3 months 7 days
Exercisable at the end of the period, weighted average remaining contractual term	4 years 4 months 13 days
Vested and expected to vest at the end of the period, weighted average remaining contractual term	7 years 3 months 7 days
Outstanding at the end of the period, aggregate intrinsic value	$ 15,409
Exercisable at the end of the period, aggregate intrinsic value	12,329
Vested and expected to vest at the end of the period, aggregate intrinsic value	15,409
Total unrecognized compensation cost related to non-vested shares	$ 25,900
Unrecognized compensation cost, weighted-average period	2 years 3 months 18 days
Total fair value of shares vested	$ 1,800
Weighted-average assumption used for grants
Dividend yield	0.00%	0.00%	0.00%
Expected volatility, minimum	76.80%	65.80%	57.30%
Expected volatility, maximum	96.80%	83.90%	61.50%
Risk-free interest rate, minimum	0.58%	0.37%	2.11%
Risk-free interest rate, maximum	1.31%	1.21%	2.53%
Expected life		6 years	6 years
Stock-based compensation
Weighted-average grant date fair values of options granted (in dollars per share)	$ 5.90	$ 1.54	$ 1.28
Exercised during the period, aggregate intrinsic value	$ 10,100	$ 1,800	$ 100
Stock-based compensation expense	$ 9,900	$ 1,700	$ 2,200
Minimum
Weighted-average assumption used for grants
Expected life	5 years 7 months 6 days
Maximum
Weighted-average assumption used for grants
Expected life	5 years 9 months 18 days
Vesting over the first year
Stock-based compensation
Vesting percentage	34.00%
Vesting over the second year
Stock-based compensation
Vesting percentage	33.00%
Vesting over the third year
Stock-based compensation
Vesting percentage	33.00%

Stockholders' Equity - Performa

Stockholders' Equity - Performance-Based Stock Options (Details) - Performance-Based Stock Options [Member] $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Stock-based compensation
Contractual term	10 years
Number of Shares
Granted (in shares) | shares	1,640,000
Outstanding at the end of the period (in shares) | shares	1,640,000
Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 6.77
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 6.77
Additional option disclosures
Outstanding at the end of the period, weighted average remaining contractual term	9 years 11 months 8 days
Total unrecognized compensation cost related to non-vested shares	$ 6.6
Total fair value of shares vested	$ 0
Weighted-average assumption used for grants
Dividend yield	0.00%
Expected volatility	77.10%
Risk-free interest rate	1.36%
Expected life	6 years 2 months 12 days
Stock-based compensation
Weighted-average grant date fair values of options granted (in dollars per share) | $ / shares	$ 4.58
Exercised during the period, aggregate intrinsic value	$ 0
Stock-based compensation expense	$ 1

Stockholders' Equity - Market-B

Stockholders' Equity - Market-Based Stock Options (Details) - Market Based Stock Options [Member] $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Stock-based compensation
Share price | $ / shares	$ 14
Threshold period of specified consecutive trading days within which common stock price to be trade to vest stock options	20 days
Minimum percentage of closing price of the Company's common stock on the market-based stock option grant date	207.00%
Contractual term	10 years
Number of Shares
Granted (in shares) | shares	3,700,000
Outstanding at the end of the period (in shares) | shares	3,700,000
Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 6.77
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 6.77
Additional option disclosures
Outstanding at the end of the period, weighted average remaining contractual term	9 years 11 months 8 days
Total unrecognized compensation cost related to non-vested shares | $	$ 17.8
Unrecognized compensation cost, weighted-average period	6 years 9 months 18 days
Total fair value of shares vested | $	$ 0
Weighted-average assumption used for grants
Dividend yield	0.00%
Expected volatility	67.80%
Risk-free interest rate	1.50%
Expected life	10 years
Stock-based compensation
Weighted-average grant date fair values of options granted (in dollars per share) | $ / shares	$ 4.87
Exercised during the period, aggregate intrinsic value | $	$ 0
Stock-based compensation expense | $	$ 0.2

Stockholders' Equity - Restrict

Stockholders' Equity - Restricted Stock Units (Details) - Service-Based RSUs - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Outstanding at the beginning of the period (in shares)	978,716
Granted (in shares)	894,344
Vested (in shares)	(722,193)
Forfeited or expired (in shares)	(23,925)
Outstanding at the end of the period (in shares)	1,126,942	978,716
Weighted Average Fair Value at Grant Date
Outstanding at the beginning of the period (in dollars per share)	$ 1.71
Granted (in dollars per share)	10.24	$ 2.56
Vested (in dollars per share)	2.54
Forfeited or expired (in dollars per share)	6.86
Outstanding at the end of the period (in dollars per share)	$ 8.08	$ 1.71
Unrecognized compensation cost	$ 6.2
Unrecognized compensation cost, weighted-average period	1 year 9 months 18 days
Stock-based compensation expense	$ 3.9	$ 1	$ 1.5
Vesting over the first year
Stock-based compensation
Vesting percentage	34.00%
Vesting over the second year
Stock-based compensation
Vesting percentage	33.00%
Vesting over the third year
Stock-based compensation
Vesting percentage	33.00%

Stockholders' Equity - Employee

Stockholders' Equity - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan $ in Millions	May 07, 2013periodshares	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Stock-based compensation
Purchase price of shares expressed as percentage of fair market value of common stock	85.00%
Number of non-concurrent offering periods | period	2
Number of shares reserved (in shares) | shares	2,500,000
Stock-based compensation expense | $		$ 0.1	$ 0	$ 0

Stockholders Equity - Amazon Wa

Stockholders Equity - Amazon Warrant (Details) - USD ($)	Jun. 14, 2021	Apr. 16, 2021	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Apr. 15, 2021
Subsidiary, Sale of Stock [Line Items]
Common stock, par value (in dollars per share)				$ 0.0001	$ 0.0001
Contra revenue charge				$ 83,641,000	$ 0	$ 0
Amazon Warrant
Subsidiary, Sale of Stock [Line Items]
Aggregate number of warrant shares (in shares)	5,625,959	53,141,755
Number of warrants vested (in shares)				14,689,935
Total discretionary fuel purchases		$ 500,000,000
Fair value of warrants outstanding				$ 44,077,779
Exercise price of the warrant (in dollars per share)	$ 13.49	$ 13.49
Exercise price premium (as a percent)		21.30%
Common stock price (in dollars per share)							$ 11.12
Aggregate number of warrant shares that may require stockholder approval (in shares)		50,595,531
Notification period to waive or modify Beneficial Ownership Limitation		61 days
Contra revenue charge				83,600,000
Customer incentive assets			$ 38,400,000
Amazon Warrant | Prepaid expenses and other current assets
Subsidiary, Sale of Stock [Line Items]
Customer incentive assets				12,400,000
Amazon Warrant | Notes receivable and other long term assets
Subsidiary, Sale of Stock [Line Items]
Customer incentive assets				22,100,000
Amazon Warrant | Maximum
Subsidiary, Sale of Stock [Line Items]
Percentage of common stock outstanding owned (as a percent)		4.999%
Amazon Warrant | Vesting over the first year
Subsidiary, Sale of Stock [Line Items]
Number of warrants vested (in shares)	1,406,490	13,283,445
Contra revenue charge			$ 76,600,000	76,600,000
Amazon Warrant | Vesting over the second year
Subsidiary, Sale of Stock [Line Items]
Contra revenue charge				$ 7,000,000

Stockholders Equity - Fair Valu

Stockholders Equity - Fair Value of Amazon Warrant (Details) - Amazon Warrant - Black-Scholes option pricing model	Jun. 14, 2021	Apr. 16, 2021
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant	0	0
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant	0.6797	0.6646
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant	0.0149	0.0159
Expected term in years
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant	9.8	10

Stockholders Equity - Amazon _2

Stockholders Equity - Amazon Warrant Activity (Details) - Amazon Warrant	12 Months Ended
	Dec. 31, 2021USD ($)shares
Class of Warrant or Right [Line Items]
Granted	58,767,714
Vested	(14,689,935)
Outstanding and unvested as of June 30, 2021 | $	$ 44,077,779

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of loss before income taxes
U.S.	$ (93,117)	$ (11,216)	$ 14,981
Foreign	(919)	(4)	(864)
Income (loss) before income taxes	(94,036)	(11,220)	14,117
Current:
State	54	80	116
Foreign	(4)	109	4
Total current	50	189	120
Deferred:
Federal	18	48	293
State	51	72	445
Total deferred	69	120	738
Total tax expense	$ 119	$ 309	$ 858
Federal income tax rate	21.00%	21.00%	21.00%
Reconciliation of the income tax provision
Computed expected tax (benefit)	$ (19,747)	$ (2,356)	$ 2,964
Nondeductible expenses	617	2,775	3,087
Tax rate differential on foreign earnings	189	(144)	245
Joint ventures	(2)	(5,059)	3,745
Amazon warrants	3,707
Tax credits	(5,299)	(4,037)	(10,314)
Other	1,463	1,559	665
Change in valuation allowance	19,191	7,571	466
Total tax expense	119	309	858
Tax benefit related to exclusion of AFTC	4,900	4,200	$ 10,500
Deferred tax assets:
Accrued expenses	5,379	4,940
Lease obligations	11,388	6,938
Alternative minimum tax and general business credits	6,787	6,233
Stock option expense	7,214	6,648
Amazon warrants	16,026
Other	3,167	1,545
Depreciation and amortization	2,582	1,635
Loss carryforwards	128,514	119,708
Total deferred tax assets	181,057	147,647
Less valuation allowance	(162,018)	(134,974)
Net deferred tax assets	19,039	12,673
Deferred tax liabilities:
Right-of-use assets	(11,266)	(6,788)
Commodity swap contracts	(649)	(1,596)
Goodwill	(2,534)	(2,221)
Investments in joint ventures and partnerships	(5,517)	(2,926)
Total deferred tax liabilities	(19,966)	(13,531)
Net deferred tax liabilities	$ (927)	$ (858)

Income Taxes - Tax Credit Carry

Income Taxes - Tax Credit Carryforwards (Details) $ in Millions	Dec. 31, 2021USD ($)
Federal
Income Taxes
Operating loss carryforwards	$ 500.1
Federal | General
Income Taxes
Tax credit carryforwards	6.8
State
Income Taxes
Operating loss carryforwards	370.9
Foreign
Income Taxes
Operating loss carryforwards	$ 2.7

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Valuation allowance
Deferred tax assets, valuation allowance	$ 162,018	$ 134,974
Net increase (decrease) in valuation allowance	27,000
Reconciliation of the total amounts of unrecognized tax benefits
Unrecognized tax benefits, if recognized, fully offset with valuation allowance	50,600
Unrecognized tax benefit at the beginning of the period	45,299	41,475
Gross increases-tax positions in current year	3,508	2,954
Gross increases-tax positions in prior year	2,142	870
Gross decreases-tax positions in prior years	(364)
Unrecognized tax benefit at the end of the period	$ 50,585	45,299	$ 41,475
Additional information on income tax
Interest expense related to uncertain tax positions		$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Long-Term Take-or-Pay Natural Gas Purchase Contracts (Details) $ in Millions	Dec. 31, 2021USD ($)
CNG supply agreement | JTA
Fixed commitments under the contract payable in future
2023	$ 0.1
Natural Gas Supply Agreement | DGS
Fixed commitments under the contract payable in future
2022	1.2
2023	$ 1.2

Commitments and Contingencies_2

Commitments and Contingencies - Long-Term Natural Gas Purchase Contracts (Details) - Long-Term Natural Gas Purchase Contracts - USD ($) $ in Millions	1 Months Ended
	Jun. 30, 2017	Dec. 31, 2020
Other Commitments [Line Items]
Term of agreement	5 years
Due in 2022		$ 1.1

Commitments and Contingencies_3

Commitments and Contingencies - bpJV Capital Call Contribution (Details) - bpJV - ADG RNG Production Facilities - USD ($) $ in Millions	Apr. 13, 2021	Dec. 31, 2021	Jan. 31, 2022	Jun. 21, 2021
Other Commitments [Line Items]
Investment commitment in joint venture	$ 30			$ 50.2
Initial contribution commitment	30
bp
Other Commitments [Line Items]
Investment commitment in joint venture	$ 50
Capital Contribution
Other Commitments [Line Items]
Capital call contribution amount		$ 143.2
Investment commitment in joint venture		71.6
Initial contribution commitment		20
Capital Contribution | Subsequent Event
Other Commitments [Line Items]
Investment commitment in joint venture			$ 51.6
Capital Contribution | bp
Other Commitments [Line Items]
Investment commitment in joint venture		71.6
Initial contribution commitment		$ 71.6

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases
Sales-type lease, interest income	$ 400	$ 500
NG Advantage
Leases
Residual value of leased asset	$ 1,000

Leases - Finance and Operating

Leases - Finance and Operating Lease Asset and Liability Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finance leases:
Land, property and equipment, gross	$ 693,689	$ 685,356
Accumulated depreciation	(431,928)	(394,445)
Total land, property and equipment, net	261,761	290,911
Current portion of finance lease obligations	$ 846	$ 840
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current portion of finance lease obligations	Current portion of finance lease obligations
Long-term portion of finance lease obligations	$ 2,427	$ 2,552
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term portion of finance lease obligations	Long-term portion of finance lease obligations
Total finance lease liabilities	$ 3,273	$ 3,392
Operating leases:
Operating lease right-of-use assets	$ 42,537	$ 25,967
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating lease right-of-use assets	Operating lease right-of-use assets
Current portion of operating lease obligations	$ 3,551	$ 2,822
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Current portion of operating lease obligations	Current portion of operating lease obligations
Long-term portion of operating lease obligations	$ 39,431	$ 23,698
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term portion of operating lease obligations	Long-term portion of operating lease obligations
Total operating lease liabilities	$ 42,982	$ 26,520
Finance Leased Assets
Finance leases:
Land, property and equipment, gross	5,617	4,915
Accumulated depreciation	(2,646)	(1,905)
Total land, property and equipment, net	$ 2,971	$ 3,010

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Finance leases:
Depreciation on assets under finance leases	$ 809	$ 733
Interest on lease liabilities	181	185
Total finance leases expense	990	918
Operating leases:
Lease expense	7,313	6,287
Lease expense on short-term leases	205	847
Variable lease expense	3,321	2,593
Sublease income	(726)	(736)
Total operating leases expense	$ 10,113	$ 8,991

Leases - Supplemental Informati

Leases - Supplemental Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases
Operating cash outflows from finance leases	$ 181	$ 185
Operating cash outflows from operating leases	5,804	5,503
Financing cash outflows from finance leases	789	1,242
Assets obtained in exchange for new finance lease liabilities	879	1,337
ROU assets obtained in exchange for operating lease liabilities	$ 19,515	$ 96
Weighted-average remaining lease term - finance leases	2 years 10 months 13 days	3 years 7 months 2 days
Weighted-average remaining lease term - operating leases	12 years 3 months 21 days	10 years 9 months 21 days
Weighted-average discount rate - finance leases	5.22%	5.27%
Weighted-average discount rate - operating leases	7.55%	8.40%

Leases - Maturities of Finance

Leases - Maturities of Finance and Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finance Leases
2022	$ 990
2023	893
2024	1,305
2025	390
Total minimum lease payments	3,578
Less amount representing interest	(305)
Present value of lease liabilities	3,273	$ 3,392
Operating Leases
2022	6,148
2023	6,037
2024	6,087
2025	6,028
2026	5,840
Thereafter	38,033
Total minimum lease payments	68,173
Less amount representing interest	(25,191)
Present value of lease liabilities	$ 42,982	$ 26,520

Leases - Maturities of Lease Re

Leases - Maturities of Lease Receivables (Details) $ in Thousands	Dec. 31, 2021USD ($)
Fiscal year:
2022	$ 1,182
2023	962
2024	962
2025	962
2026	1,034
Thereafter	2,339
Total minimum lease payments	7,441
Less amount representing interest	(1,908)
Present value of lease receivables	$ 5,533

401(k) Plan (Details)

401(k) Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Maximum percentage of base pay that can be contributed by employees through salary deferrals	90.00%
Contribution by the company	$ 1.6	$ 1.5	$ 1.3

Net Income (Loss) Per Share (De

Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to Clean Energy Fuels Corp.	$ (93,146)	$ (9,864)	$ 20,421
Weighted-average common shares outstanding	213,118,694	200,657,912	204,573,287
Dilutive effect of potential common shares from restricted stock units, stock options and stock warrants			1,414,222
Weighted-average common shares outstanding - diluted	213,118,694	200,657,912	205,987,509
Basic income (loss) per share (in dollars per share)	$ (0.44)	$ (0.05)	$ 0.10
Diluted income (loss) per share (in dollars per share)	$ (0.44)	$ (0.05)	$ 0.10

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Loss Per Share
Anti-dilutive securities (in shares)	77,048,327	10,234,330	10,817,020
Stock options
Net Loss Per Share
Anti-dilutive securities (in shares)	17,153,671	8,142,831	7,652,463
Convertibles notes
Net Loss Per Share
Anti-dilutive securities (in shares)		1,112,783	3,164,557
Restricted stock units
Net Loss Per Share
Anti-dilutive securities (in shares)	1,126,942	978,716
Amazon warrant shares
Net Loss Per Share
Anti-dilutive securities (in shares)	58,767,714

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
TOTALEnergies S.E.
Related Party Transaction [Line Items]
Proceeds from related party	$ 4,900	$ 7,800
Receivables from related party	1,400	900
Related party expense	2,000	700
Payable to related parties	100	0
SAFE&CEC S.r.l.
Related Party Transaction [Line Items]
Proceeds from related party	200	1,200
Receivables from related party		200
Related party expense	9,600	4,800
Payable to related parties	200	$ 900
TotalEnergies JV and bpJV
Related Party Transaction [Line Items]
Proceeds from related party	400
Receivables from related party	$ 400

Reportable Segments and Geogr_3

Reportable Segments and Geographic Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Geographic Information
Total revenue	$ 255,646	$ 291,724	$ 344,065
Total operating income (loss)	(95,048)	(9,844)	9,928
Total long-lived assets	441,400	383,665	415,774
United States
Geographic Information
Total revenue	252,310	281,546	338,549
Total operating income (loss)	(94,157)	(9,853)	10,805
Total long-lived assets	440,770	383,463	415,548
Canada
Geographic Information
Total revenue	3,336	10,178	5,516
Total operating income (loss)	(891)	9	(877)
Total long-lived assets	$ 630	$ 202	$ 226

Concentrations (Details)

Concentrations (Details) - Natural gas expense - Supplier concentration	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
One Customer
Supplier Concentrations
Concentration risk, percentage		10.00%
Top Three Customers
Supplier Concentrations
Concentration risk, percentage	10.00%

Subsequent Events (Details)

Subsequent Events (Details) $ / shares in Units, $ in Thousands	1 Months Ended	2 Months Ended	12 Months Ended
	Jan. 31, 2022USD ($)installment	Feb. 14, 2022USD ($)$ / sharesshares	Dec. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)
Subsequent Event [Line Items]
Repayments of borrowing under revolving line of credit			$ 1,450
Repurchase of common stock (in shares) | shares			452,700
Cost to repurchase common stock			$ 2,916	$ 14,647
Amount utilized under the repurchase plan			$ 17,400
Subsequent Event
Subsequent Event [Line Items]
Repurchase of common stock (in shares) | shares		511,010
Cost to repurchase common stock		$ 3,000
Share price | $ / shares		$ 5.85
Amount utilized under the repurchase plan		$ 20,400
Authorized funds remaining under the Repurchase Program		$ 29,600
Subsequent Event | NG Advantage debt | Berkshire Bank
Subsequent Event [Line Items]
Repayments of borrowing under revolving line of credit	$ 11,100
Release of restricted cash	7,000
Subsequent Event | NG Advantage debt | Berkshire Term Loan 2 | Berkshire Bank
Subsequent Event [Line Items]
Debt issuance amount	$ 14,000
Interest rate (as a percent)	5.00%
Number of monthly installments | installment	59
Repayments of cash payoff for borrowing under revolving line of credit	$ 10,400
Lender deposits	800
Subsequent Event | Plains Credit Facility
Subsequent Event [Line Items]
Remaining borrowing capacity	11,000
Subsequent Event | Plains Credit Facility | Berkshire Bank
Subsequent Event [Line Items]
Outstanding line of credit	$ 7,000

Schedule II_ Valuation and Qu_2

Schedule II: Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowances for Doubtful Trade Receivables
Movement in valuation and qualifying accounts
Balance at the beginning of the period	$ 1,335	$ 2,412	$ 1,919
Charges (benefit) to operations	77	796	908
Deductions	(207)	(1,873)	(415)
Balance at the end of the period	1,205	1,335	2,412
Allowance for Doubtful Notes Receivables
Movement in valuation and qualifying accounts
Balance at the beginning of the period	4,105	3,331	4,163
Charges (benefit) to operations	650	1,250	931
Deductions		(476)	(1,763)
Balance at the end of the period	$ 4,755	$ 4,105	$ 3,331