Clean Energy Fuels (CLNE) 10-Q 8 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 01, 2019
Document and Entity Information
Entity Registrant Name	Clean Energy Fuels Corp.
Entity Central Index Key	0001368265
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (in shares)		204,709,929
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Shell Company	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash, cash equivalents and current portion of restricted cash	$ 41,666	$ 30,624
Short-term investments	66,584	65,646
Accounts receivable, net of allowance for doubtful accounts of $1,919 and $2,074 as of December 31, 2018 and June 30, 2019, respectively	60,567	68,865
Other receivables	9,408	15,544
Derivative assets, related party	655	1,508
Inventory	33,870	34,975
Prepaid expenses and other current assets	9,043	8,444
Total current assets	221,793	225,606
Operating lease right-of-use assets	24,490	0
Land, property and equipment, net	328,630	350,568
Long-term portion of restricted cash	4,848	4,000
Notes receivable and other long-term assets, net	17,968	17,470
Long-term portion of derivative assets, related party	5,041	8,824
Investments in other entities	26,072	26,079
Goodwill	64,328	64,328
Intangible assets, net	1,704	2,207
Total assets	694,874	699,082
Current liabilities:
Current portion of debt	55,562	4,712
Current portion of finance lease obligations	654	693
Current portion of operating lease obligations	3,570	0
Accounts payable	16,462	19,024
Accrued liabilities	39,763	48,469
Deferred revenue	7,438	7,361
Total current liabilities	123,449	80,259
Long-term portion of debt	24,912	75,003
Long-term portion of finance lease obligations	3,236	3,776
Long-term portion of operating lease obligations	22,245
Other long-term liabilities	12,901	15,035
Total liabilities	186,743	174,073
Commitments and contingencies (Note 17)
Stockholders’ equity:
Preferred stock, $0.0001 par value. Authorized 1,000,000 shares; issued and outstanding no shares	0	0
Common stock, $0.0001 par value. Authorized 304,000,000 shares as of December 31, 2018 and June 30, 2019, respectively; issued and outstanding 203,599,892 shares and 204,655,146 shares as of December 31, 2018 and June 30, 2019, respectively	20	20
Additional paid-in capital	1,201,340	1,198,769
Accumulated deficit	(704,982)	(688,653)
Accumulated other comprehensive loss	(1,440)	(2,138)
Total Clean Energy Fuels Corp. stockholders’ equity	494,938	507,998
Noncontrolling interest in subsidiary	13,193	17,011
Total stockholders’ equity	508,131	525,009
Total liabilities and stockholders’ equity	$ 694,874	$ 699,082

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,074	$ 1,919
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	304,000,000	304,000,000
Common stock, issued (in shares)	204,655,146	203,599,892
Common stock, outstanding (in shares)	204,655,146	203,599,892

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Total revenue	$ 72,318	$ 70,467	$ 150,016	$ 172,870
Cost of sales (exclusive of depreciation and amortization shown separately below):
Change in fair value of derivative warrants	(17)	(70)	1,597	(92)
Selling, general and administrative	17,933	19,938	36,368	38,797
Depreciation and amortization	12,605	13,332	25,084	26,133
Total operating expenses	78,131	78,851	169,487	165,285
Operating income (loss)	(5,813)	(8,384)	(19,471)	7,585
Interest expense	(1,842)	(4,527)	(3,733)	(9,030)
Interest income	567	489	1,147	1,064
Other income (expense), net	93	79	2,764	67
Loss from equity method investments	(33)	(729)	(500)	(2,197)
Income (loss) before income taxes	(7,028)	(13,072)	(19,793)	(2,511)
Income tax expense	(66)	(89)	(126)	(177)
Net income (loss)	(7,094)	(13,161)	(19,919)	(2,688)
Loss attributable to noncontrolling interest	1,711	1,186	3,590	2,935
Net income (loss) attributable to Clean Energy Fuels Corp.	$ (5,383)	$ (11,975)	$ (16,329)	$ 247
Income (loss) per share:
Basic (in dollars per share)	$ (0.03)	$ (0.07)	$ (0.08)	$ 0
Diluted (in dollars per share)	$ (0.03)	$ (0.07)	$ (0.08)	$ 0
Weighted-average common shares outstanding:
Basic (in shares)	204,653,723	162,613,316	204,426,459	157,432,786
Diluted (in shares)	204,653,723	162,613,316	204,426,459	161,682,245
Product revenue
Revenue:
Total revenue	$ 59,691	$ 61,120	$ 128,139	$ 153,371
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	40,121	41,396	94,551	91,595
Service revenue
Revenue:
Total revenue	12,627	9,347	21,877	19,499
Cost of sales (exclusive of depreciation and amortization shown separately below):
Cost of sales	$ 7,489	$ 4,255	$ 11,887	$ 8,852

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income (loss)	$ (7,094)	$ (13,161)	$ (19,919)	$ (2,688)
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2018 and 2019	321	(25)	629	(104)
Unrealized gains on available-for-sale securities, net of $0 tax in 2018 and 2019	3	549	69	603
Total other comprehensive income (loss)	324	524	698	499
Comprehensive income (loss)	(6,770)	(12,637)	(19,221)	(2,189)
Clean Energy Fuels Corp.
Net income (loss)	(5,383)	(11,975)	(16,329)	247
Other comprehensive income, net of tax:
Foreign currency translation adjustments, net of $0 tax in 2018 and 2019	321	(25)	629	(104)
Unrealized gains on available-for-sale securities, net of $0 tax in 2018 and 2019	3	549	69	603
Total other comprehensive income (loss)	324	524	698	499
Comprehensive income (loss)	(5,059)	(11,451)	(15,631)	746
Noncontrolling Interest
Net income (loss)	(1,711)	(1,186)	(3,590)	(2,935)
Other comprehensive income, net of tax:
Comprehensive income (loss)	$ (1,711)	$ (1,186)	$ (3,590)	$ (2,935)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, tax	$ 0	$ 0	$ 0	$ 0
Unrealized (losses) gains on available-for-sale securities, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiary
Beginning balance (in shares) at Dec. 31, 2017		151,650,969
Beginning balance at Dec. 31, 2017	$ 449,658	$ 15	$ 1,111,432	$ (683,570)	$ (887)	$ 22,668
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		863,581
Issuance of common stock, net of offering costs	110		110
Stock-based compensation	1,898		1,898
Net income (loss)	10,473			12,222		(1,749)
Other comprehensive income (loss)	(25)				(25)
Ending balance (in shares) at Mar. 31, 2018		152,514,550
Ending balance at Mar. 31, 2018	460,821	$ 15	1,113,440	(672,641)	(912)	20,919
Beginning balance (in shares) at Dec. 31, 2017		151,650,969
Beginning balance at Dec. 31, 2017	449,658	$ 15	1,111,432	(683,570)	(887)	22,668
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(2,688)					(2,935)
Other comprehensive income (loss)	499
Ending balance (in shares) at Jun. 30, 2018		203,430,778
Ending balance at Jun. 30, 2018	530,150	$ 20	1,195,401	(684,616)	(388)	19,733
Beginning balance (in shares) at Mar. 31, 2018		152,514,550
Beginning balance at Mar. 31, 2018	460,821	$ 15	1,113,440	(672,641)	(912)	20,919
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		50,916,228
Issuance of common stock, net of offering costs	80,758	$ 5	80,753
Stock-based compensation	1,208		1,208
Net income (loss)	(13,161)			(11,975)		(1,186)
Other comprehensive income (loss)	524				524
Ending balance (in shares) at Jun. 30, 2018		203,430,778
Ending balance at Jun. 30, 2018	$ 530,150	$ 20	1,195,401	(684,616)	(388)	19,733
Beginning balance (in shares) at Dec. 31, 2018	203,599,892	203,599,892
Beginning balance at Dec. 31, 2018	$ 525,009	$ 20	1,198,769	(688,653)	(2,138)	17,011
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		1,052,040
Issuance of common stock, net of offering costs	175		175
Stock-based compensation	1,246		1,246
Net income (loss)	(12,825)			(10,946)		(1,879)
Other comprehensive income (loss)	374				374
Increase in ownership in subsidiary			228			(228)
Ending balance (in shares) at Mar. 31, 2019		204,651,932
Ending balance at Mar. 31, 2019	$ 513,979	$ 20	1,200,418	(699,599)	(1,764)	14,904
Beginning balance (in shares) at Dec. 31, 2018	203,599,892	203,599,892
Beginning balance at Dec. 31, 2018	$ 525,009	$ 20	1,198,769	(688,653)	(2,138)	17,011
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(19,919)					(3,590)
Other comprehensive income (loss)	$ 698
Ending balance (in shares) at Jun. 30, 2019	204,655,146	204,655,146
Ending balance at Jun. 30, 2019	$ 508,131	$ 20	1,201,340	(704,982)	(1,440)	13,193
Beginning balance (in shares) at Mar. 31, 2019		204,651,932
Beginning balance at Mar. 31, 2019	513,979	$ 20	1,200,418	(699,599)	(1,764)	14,904
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net of offering costs (in shares)		3,214
Issuance of common stock, net of offering costs	4		4
Stock-based compensation	918		918
Net income (loss)	(7,094)			(5,383)		(1,711)
Other comprehensive income (loss)	$ 324				324
Ending balance (in shares) at Jun. 30, 2019	204,655,146	204,655,146
Ending balance at Jun. 30, 2019	$ 508,131	$ 20	$ 1,201,340	$ (704,982)	$ (1,440)	$ 13,193

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income (loss)	$ (19,919)	$ (2,688)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	25,084	26,133
Provision for doubtful accounts, notes and inventory	646	407
Stock-based compensation expense	2,164	3,106
Change in fair value of derivative instruments	5,992	(92)
Amortization of discount and debt issuance cost	(429)	488
Realized loss on sale of available-for-sale debt securities	0	103
Loss (gain) on disposal of property and equipment	(3,967)	1,048
Loss from equity method investments	500	2,197
Non-cash lease expense	1,695
Changes in operating assets and liabilities:
Accounts and other receivables	9,361	(2,183)
Inventory	656	(2,189)
Prepaid expenses and other assets	(1,027)	(1,795)
Operating lease liabilities	(1,860)
Accounts payable	560	(3,448)
Deferred revenue	(2,723)	3,269
Accrued expenses and other	(7,950)	(1,432)
Net cash provided by operating activities	8,783	22,924
Cash flows from investing activities:
Purchases of short-term investments	(72,029)	(250,311)
Maturities and sales of short-term investments	71,666	180,961
Purchases of and deposits on property and equipment	(7,743)	(9,830)
Payments on and proceeds from sales of loans receivable	(281)	213
Cash received from sale of certain assets of subsidiary, net	5,016	871
Proceeds from disposal of property and equipment	6,337	0
Net cash (used in) provided by investing activities	2,966	(78,096)
Cash flows from financing activities:
Issuances of common stock	179	83,419
Fees paid for issuances of common stock	0	(455)
Proceeds from debt instruments	3,394	6,261
Repayment of finance lease obligations and debt instruments	(3,533)	(27,724)
Payments for debt issuance costs	(29)	0
Net cash provided by financing activities	11	61,501
Effect of exchange rates on cash, cash equivalents and restricted cash	130	(130)
Net increase in cash, cash equivalents and restricted cash	11,890	6,199
Cash, cash equivalents and restricted cash, beginning of period	34,624	37,208
Cash, cash equivalents and restricted cash, end of period	46,514	43,407
Supplemental disclosure of cash flow information:
Income taxes paid	32	160
Interest paid, net of approximately $106 and $178 capitalized, respectively	$ 2,590	$ 6,743

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Interest paid, capitalized	$ 178	$ 106

General

General	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General Nature of Business Clean Energy Fuels Corp., together with its majority and wholly owned subsidiaries (hereinafter collectively referred to as the “Company,” unless the context or the use of the term indicates or requires otherwise) is engaged in the business of selling natural gas as an alternative fuel for vehicle fleets and related natural gas fueling solutions to its customers, primarily in the United States and Canada. The Company’s principal business is supplying renewable natural gas (“RNG”), compressed natural gas (“CNG”) and liquefied natural gas (“LNG”) (RNG can be delivered in the form of CNG or LNG) for light, medium and heavy-duty vehicles and providing operation and maintenance (“O&M”) services for public and private vehicle fleet customer stations. As a comprehensive solution provider, the Company also designs, builds, operates and maintains fueling stations; sells and services natural gas fueling compressors and other equipment used in CNG stations and LNG stations; offers assessment, design and modification solutions to provide operators with code-compliant service and maintenance facilities for natural gas vehicle fleets; transports and sells CNG and LNG via “virtual” natural gas pipelines and interconnects; procures and sells RNG; sells tradable credits it generates by selling RNG and conventional natural gas as a vehicle fuel, including Renewable Identification Numbers (“RIN Credits” or “RINs”) under the federal Renewable Fuel Standard Phase 2 and credits under the California and the Oregon Low Carbon Fuel Standards (collectively, “LCFS Credits”); helps its customers acquire and finance natural gas vehicles; and obtains federal, state and local credits, grants and incentives. Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to state fairly the Company’s consolidated financial position as of June 30, 2019 , and results of operations, comprehensive income (loss) and cash flows for the three and six months ended June 30, 2018 and 2019 . All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and six month periods ended June 30, 2018 and 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any future year. Certain information and disclosures normally included in the notes to consolidated financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”), but the resultant disclosures contained herein are in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) as they apply to interim reporting. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2018 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 12, 2019. Reclassifications Certain prior period amounts have been reclassified in the condensed consolidated balance sheets and condensed consolidated statements of operations and cash flows to conform to the current period presentation. These reclassifications had no material impact on the Company’s consolidated financial position, results of operations, or cash flows as previously reported. Use of Estimates The preparation of condensed consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying condensed consolidated financial statements and these notes. Actual results could differ from those estimates and may result in material effects on the Company’s operating results and financial position. Significant estimates made in preparing the accompanying condensed consolidated financial statements include (but are not limited to) those related to revenue recognition, fair value measurements, goodwill and long-lived asset valuations and impairment assessments, income tax valuations and stock-based compensation expense.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers Revenue Recognition Overview The Company recognizes revenue when control of the promised goods or services is transferred to its customers, in an amount that reflects the consideration to which it expects to be entitled in exchange for the goods or services. To achieve that core principle, a five-step approach is applied: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue allocated to each performance obligation when the Company satisfies the performance obligation. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer, and is the unit of account for revenue recognition. The table below presents the Company’s revenue disaggregated by revenue source. The Company is generally the principal in its customer contracts because it has control over the goods and services prior to them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities. Three Months Ended Six Months Ended 2018 2019 2018 2019 Volume -related (1) $ 62,642 $ 66,260 $ 129,978 $ 140,788 Station construction sales 5,781 5,943 11,579 9,113 Alternative fuels excise tax credit (“AFTC”) 1,382 — 26,863 — Other 662 115 4,450 115 Total revenue $ 70,467 $ 72,318 $ 172,870 $ 150,016 (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. The amounts are classified as revenue because the Company’s commodity swap contracts are used to economically offset the risk associated with the diesel -to -natural gas price spread resulting from anticipated customer fueling contracts under the Company’s Zero Now truck financing program. See Note 6 for more information about these derivative instruments. For the three and six months ended June 30, 2019 , changes in the fair value of commodity swaps and customer fueling contracts amounted to a gain of $565 and a loss of $ 4,395 , respectively. Remaining Performance Obligations Remaining performance obligations represent the transaction price of customer orders for which the work has not been performed. As of June 30, 2019 , the aggregate amount of the transaction price allocated to remaining performance obligations was $10,825 which related to the Company’s station construction sale contracts. The Company expects to recognize revenue on the remaining performance obligations under these contracts over the next 12 to 24 months. For volume -related revenue, the Company has elected to apply an optional exemption, which waives the requirement to disclose the remaining performance obligation for revenue recognized through the ‘ right to invoice’ practical expedient. Contract Balances The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets), and customer advances and deposits (contract liabilities) in the accompanying condensed consolidated balance sheets. Changes in the contract asset and liability balances during the six months ended June 30, 2019 , were not materially impacted by any factors outside the normal course of business. As of December 31, 2018 and June 30, 2019 , the Company’s contract balances were as follows: December 31, 2018 June 30, 2019 Receivables, net $ 68,865 $ 60,567 Contract Assets - Current $ 656 $ 893 Contract Assets - Noncurrent 3,825 3,654 Contract Assets - Total $ 4,481 $ 4,547 Contract Liabilities - Current $ 5,513 $ 4,896 Contract Liabilities - Noncurrent 9,844 7,044 Contract Liabilities - Total $ 15,357 $ 11,940 Receivables, Net “Receivables, net” in the accompanying condensed consolidated balance sheets include amounts billed and currently due from customers. The amounts due are stated at their net estimated realizable value. The Company maintains an allowance for doubtful accounts to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of customer creditworthiness, historical payment experience, and the age of outstanding receivables. Contract Assets Contract assets include unbilled amounts typically resulting from the Company’s station construction sale contracts, when the cost-to-cost method of revenue recognition is utilized and revenue recognized exceeds the amount billed to the customer, and right to payment is not just subject to the passage of time. Amounts may not exceed their net realizable value. Contract assets are classified as current or noncurrent based on the timing of billings. The current portion is included in “Prepaid expenses and other current assets” and the noncurrent portion is included in “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets. Contract Liabilities Contract liabilities consist of billings in excess of revenue recognized from the Company’s station construction sale contracts and payments received primarily from a customer of NG Advantage, LLC (“NG Advantage”) in advance of the performance obligations. Deferred revenue is classified as current or noncurrent based on when the revenue is expected to be recognized. The current portion and noncurrent portion of deferred revenue are included in “Deferred revenue” and “Other long -term liabilities,” respectively, in the accompanying condensed consolidated balance sheets. Revenue recognized during the six months ended June 30, 2018 related to the Company’s contract liability balances as of December 31, 2017 was $1,479 . The decrease in the contract liability balances for the six months ended June 30, 2019 is primarily driven by billings in excess of revenue recognized, offset by $4,412 of revenue recognized related to the Company’s contract liability balances as of December 31, 2018 .

Investments in Other Entities a

Investments in Other Entities and Noncontrolling Interest in a Subsidiary	6 Months Ended
	Jun. 30, 2019
Business Combinations [Abstract]
Investments in Other Entities and Noncontrolling Interest in a Subsidiary	Investments in Other Entities and Noncontrolling Interest in a Subsidiary SAFE&CEC S.r.l. On November 26, 2017, the Company, through its former subsidiary IMW Industries Ltd. (formerly known as Clean Energy Compression Corp.) (“CEC”), entered into an investment agreement with Landi Renzo S.p.A. (“LR”), an alternative fuels company based in Italy. Pursuant to the investment agreement, the Company and LR agreed to combine their respective natural gas compressor subsidiaries, CEC and SAFE S.p.A, in a new company known as “SAFE&CEC S.r.l.” (such combination transaction is referred to as the “CEC Combination”). SAFE&CEC S.r.l. is focused on manufacturing, selling and servicing natural gas fueling compressors and related equipment for the global natural gas fueling market. As of the closing of the CEC Combination on December 29, 2017, the Company owns 49% of SAFE&CEC S.r.l. and LR owns 51% of SAFE&CEC S.r.l. The Company accounts for its interest in SAFE&CEC S.r.l. using the equity method of accounting because the Company does not control but has the ability to exercise significant influence over SAFE&CEC S.r.l.’s operations. The Company recorded a loss from this investment of $706 and $6 for the three months ended June 30, 2018 and 2019 , respectively, and $2,147 and $446 for the six months ended June 30, 2018 and 2019 , respectively. The Company has an investment balance in SAFE&CEC S.r.l. of $23,372 and $23,419 as of December 31, 2018 and June 30, 2019 , respectively. NG Advantage On October 14, 2014, the Company entered into a Common Unit Purchase Agreement (“UPA”) with NG Advantage for a 53.3% controlling interest in NG Advantage. NG Advantage is engaged in the business of transporting CNG in high-capacity trailers to industrial and institutional energy users, such as hospitals, food processors, manufacturers and paper mills that do not have direct access to natural gas pipelines. NG Advantage has entered into an arrangement with BP Products North America (“BP”) for the supply, sale and reservation of a specified volume of CNG transportation capacity until March 2022. On February 28, 2018, the Company entered into a guaranty agreement with NG Advantage and BP pursuant to which the Company guarantees NG Advantage’s payment obligations to BP in the event of default by NG Advantage under the supply arrangement, in an amount up to an aggregate of $30,000 plus related fees. This guaranty is in effect until thirty days following the Company’s notice to BP of its termination. As initial consideration for the guaranty agreement, NG Advantage issued to the Company 19,660 common units, which increased the Company’s controlling interest in NG Advantage from 53.3% to 53.5% . On October 1, 2018, the Company purchased 1,000,001 common units from NG Advantage for an aggregate cash purchase price of $5,000 . This purchase increased Clean Energy’s controlling interest in NG Advantage from 53.5% 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% as of June 30, 2019 . On February 15, 2019, NG Advantage and the Company entered into a transaction pursuant to which the Company agreed to lend to NG Advantage up to $5,000 in accordance with the terms of a delayed draw convertible promissory note (the “2019 Note”). NG Advantage simultaneously drew $2,500 under the 2019 Note, and on April 15, 2019, NG Advantage drew the remaining $2,500 under the 2019 Note. As discussed below, on June 28, 2019, all unpaid principal and accrued interest under the 2019 Note was subsumed within the 2019 Convertible Note (as defined below). On May 17, 2019, the Company agreed to lend to NG Advantage up to $500 in accordance with the terms of the promissory note (the “2019 Bridge Loan”). On June 11, 2019, NG Advantage drew $144 under the 2019 Bridge Loan. As discussed below, on June 28, 2019, all unpaid principal and accrued interest under the 2019 Bridge Loan was subsumed within the 2019 Convertible Note. On June 28, 2019, the Company agreed to lend to NG Advantage up to $15,188 in accordance with the terms of the convertible promissory note (the “2019 Convertible Note”). NG Advantage simultaneously drew $3,500 under the 2019 Convertible Note. The outstanding principal and accrued interest under the 2019 Note and 2019 Bridge Loan were incorporated into the 2019 Convertible Note, which resulted in the cancellation of the 2019 Note and 2019 Bridge Loan. All unpaid principal and accrued interest is due on the earlier of December 31, 2019 or in the event of default. In connection with the 2019 Convertible Note, NG Advantage issued to the Company a warrant to purchase 86,879 common units. As of June 30, 2019 , NG Advantage had an outstanding balance of $8,688 under the 2019 Convertible Note. This intercompany transaction has been eliminated in consolidation. The Company recorded a loss attributable to the noncontrolling interest in NG Advantage of $1,186 and $1,711 for the three months ended June 30, 2018 and 2019 , respectively and $2,935 and $3,590 for the six months ended June 30, 2018 and 2019 , respectively. The value of the noncontrolling interest was $17,011 and $13,193 as of December 31, 2018 and June 30, 2019 , respectively.

Cash, Cash Equivalents, and Res

Cash, Cash Equivalents, and Restricted Cash	6 Months Ended
	Jun. 30, 2019
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash Cash, cash equivalents and restricted cash as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Current assets: Cash and cash equivalents $ 29,844 $ 40,886 Restricted cash - standby letter of credit 30 30 Restricted cash - held in escrow 750 750 Total cash, cash equivalents and current portion of restricted cash $ 30,624 $ 41,666 Long-term assets: Restricted cash - standby letter of credit $ 4,000 $ 4,000 Restricted cash - held in escrow — 848 Total long-term portion of restricted cash $ 4,000 $ 4,848 Total cash, cash equivalents and restricted cash $ 34,624 $ 46,514 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 $28,524 and $39,556 as of December 31, 2018 and June 30, 2019 , respectively. The Company classifies restricted cash as short-term and a current asset if the cash is expected to be used in operations within a year or to acquire a current asset. Otherwise, the restricted cash is classified as long-term.

Short-term Investments

Short-term Investments	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Short-term Investments	Short-term Investments Short-term investments include available-for-sale debt securities and certificates of deposit. Available-for-sale debt securities are carried at fair value, inclusive of unrealized gains and losses. Unrealized gains and losses for debt securities are recognized in other comprehensive income, net of applicable income taxes. Gains or losses on sales of available-for-sale debt securities are recognized on the specific identification basis. The Company reviews available-for-sale debt securities for other-than-temporary declines in fair value below their cost basis each quarter and whenever events or changes in circumstances indicate that the cost basis of an asset may not be recoverable. This evaluation is based on a number of factors, including the length of time and the extent to which the fair value has been below its cost basis and adverse conditions related specifically to the security, including any changes to the credit rating of the security. As of June 30, 2019 , the Company believes its carrying values for its available-for-sale debt securities are properly recorded. Short-term investments as of December 31, 2018 consisted of the following: Amortized Cost Gross Unrealized Losses Estimated Fair Value Municipal bonds and notes $ 9,210 $ (19 ) $ 9,191 Zero coupon bonds 29,823 (28 ) 29,795 Corporate bonds 26,175 (22 ) 26,153 Certificates of deposit 507 — 507 Total short-term investments $ 65,715 $ (69 ) $ 65,646 Short-term investments as of June 30, 2019 consisted of the following: Amortized Cost Gross Unrealized Gains (Losses) Estimated Fair Value Municipal bonds and notes $ 15,265 $ 2 $ 15,267 Zero coupon bonds 35,514 (2 ) 35,512 Corporate bonds 15,288 — 15,288 Certificates of deposit 517 — 517 Total short-term investments $ 66,584 $ — $ 66,584

Derivative Instruments and Hedg

Derivative Instruments and Hedging Activities	6 Months Ended
	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities In October 2018, the Company executed two commodity swap contracts with Total Gas & Power North America, an affiliate of TOTAL and THUSA (as defined in Notes 15 and 12 , respectively), for a total of five million diesel gallons annually from April 1, 2019 to June 30, 2024. These commodity swap contracts are used to manage diesel price fluctuation risks related to the natural gas fuel supply commitments the Company makes in its fueling agreements with fleet operators that participate in the Zero Now truck financing program. These contracts are not designated as accounting hedges and as a result, changes in the fair value of derivative instruments are recognized as earnings in “Product revenue” in the accompanying condensed consolidated statements of operations. During the six months ended June 30, 2019, the Company entered into fueling agreements with fleet operators under the Zero Now truck financing program. The fueling agreements contain a pricing feature indexed to diesel, which the Company evaluated to be embedded 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 condensed consolidated statements of operations. Derivatives as of December 31, 2018 consisted of the following: Gross Amounts Recognized Gross Amounts Offset Net Amount Presented Assets: Commodity swaps: Current portion of derivative assets, related party $ 1,508 $ — $ 1,508 Long-term portion of derivative assets, related party 8,824 — 8,824 Total derivative assets $ 10,332 $ — $ 10,332 Derivatives and embedded derivatives as of June 30, 2019 consisted of the following: Gross Amounts Recognized Gross Amounts Offset Net Amount Presented Assets: Commodity swaps: Current portion of derivative assets, related party $ 655 $ — $ 655 Long-term portion of derivative assets, related party 5,041 — 5,041 Fueling agreements: Prepaid expenses and other current assets 134 — 134 Notes receivable and other long-term assets, net 316 — 316 Total derivative assets $ 6,146 $ — $ 6,146 As of December 31, 2018 and June 30, 2019 , the Company had a total volume on open commodity swap contracts of 25.0 million and 24.4 million diesel gallons at a weighted -average price of approximately $3.18 and $2.82 per gallon, respectively. The following table reflects the weighted -average price of open commodity swap contracts as of December 31, 2018 and June 30, 2019 , by year with associated volumes, respectively: December 31, 2018 June 30, 2019 Year Volumes (Diesel Gallons) Weighted -Average Price per Diesel Gallon Volumes (Diesel Gallons) Weighted -Average Price per Diesel Gallon 2019 3,125,000 $ 3.18 2,500,000 $ 2.92 2020 5,000,000 $ 3.18 5,000,000 $ 2.82 2021 5,000,000 $ 3.18 5,000,000 $ 2.82 2022 5,000,000 $ 3.18 5,000,000 $ 2.82 2023 5,000,000 $ 3.18 5,000,000 $ 2.82 2024 1,875,000 $ 3.18 1,875,000 $ 2.62

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 truck financing program (see Note 6 ). Under the income approach, the Company used a discounted cash flow (“DCF”) model in which cash flows anticipated over the term of the contracts are discounted to their present value using an expected discount rate. The discount rate used for cash flows reflects the specific risks in spot and forward rates and credit valuation adjustments. This valuation approach is considered a Level 3 fair value measurement. The significant unobservable inputs used in the fair value measurement of the Company’s derivative instruments are Ultra-Low Sulfur Diesel (“ULSD”) forward prices and differentials from ULSD to Petroleum Administration for Defense District (“PADD”) regions. Significant increases (decreases) in any of those inputs in isolation would result in a significantly lower (higher) fair value measurement. Generally, a change in the ULSD forward prices is accompanied by a directionally opposite but less extreme change in the ULSD-PADD differential. The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2018 and June 30, 2019 , respectively: December 31, 2018 June 30, 2019 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve $1.71 - $1.79 $1.75 $1.80 - $1.86 $1.83 Historical Differential to PADD 3 Diesel $0.76 - $1.16 $0.89 $0.76 - $1.16 $0.90 Historical Differential to PADD 5 Diesel $1.22 - $2.12 $1.55 $1.25 - $2.30 $1.65 The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now truck financing program based on the following inputs as of June 30, 2019 : June 30, 2019 Significant Unobservable Inputs Input Range Weighted Average ULSD Gulf Coast Forward Curve $1.80 - $1.86 $1.83 Historical Differential to PADD 5 Diesel $1.25 - $2.30 $1.65 Historical Differential to PADD 1B Diesel $1.00 - $1.60 $1.26 The Company’s liability-classified warrants, which were all issued by NG Advantage, are classified within Level 3 because the Company uses the Black-Scholes option pricing model to estimate the fair value based on inputs that are not observable in any market. There were no transfers of assets or liabilities between Level 1, Level 2, or Level 3 of the fair value hierarchy as of December 31, 2018 or June 30, 2019 . The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2018 and June 30, 2019 , respectively: December 31, 2018 Level 1 Level 2 Level 3 Assets: Available-for-sale securities (1) : Municipal bonds and notes $ 9,191 $ — $ 9,191 $ — Zero coupon bonds 29,795 — 29,795 — Corporate bonds 26,153 — 26,153 — Certificates of deposit (1) 507 — 507 — Commodity swap contracts (2) 10,332 — — 10,332 Embedded derivatives (3) — — — — Liabilities: Warrants (4) $ 1,079 $ — $ — $ 1,079 June 30, 2019 Level 1 Level 2 Level 3 Assets: Available-for-sale debt securities (1) : Municipal bonds and notes $ 15,267 $ — $ 15,267 $ — Zero coupon bonds 35,512 — 35,512 — Corporate bonds 15,288 — 15,288 — Certificates of deposit (1) 517 — 517 — Commodity swap contracts (2) 5,696 — — 5,696 Embedded derivatives (3) 450 — — 450 Liabilities: Warrants (4) $ 2,676 $ — $ — $ 2,676 (1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information. (2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (3) Included in “Prepaid expenses and other current assets” and “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (4) Included in “Other long-term liabilities” in the accompanying condensed consolidated balance sheets. The following table provides a reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis as shown in the tables above that used significant unobservable inputs (Level 3): Assets: Commodity Swap Contracts Assets: Embedded Derivatives Liabilities: Warrants Balance as of December 31, 2017 $ — $ — $ (536 ) Gain (loss) included in earnings — — 92 Balance as of June 30, 2018 $ — $ — $ (444 ) Balance as of December 31, 2018 $ 10,332 $ — $ (1,079 ) Settlements, net 209 — — Gain (loss) included in earnings (4,845 ) 450 (1,597 ) Balance as of June 30, 2019 $ 5,696 $ 450 $ (2,676 ) Other Financial Assets and Liabilities The carrying amounts of the Company’s cash, cash equivalents and restricted cash, receivables and payables approximate fair value due to the short-term nature of those instruments. The carrying amounts of the Company’s debt instruments approximated their respective fair values as of December 31, 2018 and June 30, 2019 . The fair values of these debt instruments were estimated using a discounted cash flow analysis based on interest rates offered on loans with similar terms to borrowers of similar credit quality, which are Level 3 inputs. See Note 12 for more information about the Company’s debt instruments.

Other Receivables

Other Receivables	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Other Receivables	Other Receivables Other receivables as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Loans to customers to finance vehicle purchases $ 276 $ 1,821 Accrued customer billings 6,261 5,897 Fuel tax credits 434 434 Other 8,573 1,256 Total other receivables $ 15,544 $ 9,408

Inventory

Inventory	6 Months Ended
	Jun. 30, 2019
Inventory Disclosure [Abstract]
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. Inventory as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Raw materials and spare parts $ 34,890 $ 33,781 Finished goods 85 89 Total inventory $ 34,975 $ 33,870

Land, Property and Equipment

Land, Property and Equipment	6 Months Ended
	Jun. 30, 2019
Property, Plant and Equipment [Abstract]
Land, Property and Equipment	Land, Property and Equipment Land, property and equipment as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Land $ 3,681 $ 3,681 LNG liquefaction plants 94,633 94,633 Station equipment 319,119 315,547 Trailers 75,901 75,242 Other equipment 97,268 98,424 Construction in progress 73,485 75,995 664,087 663,522 Less: accumulated depreciation (313,519 ) (334,892 ) Total land, property and equipment, net $ 350,568 $ 328,630 Included in “Land, property and equipment, net” are capitalized software costs of $29,344 and $29,987 as of December 31, 2018 and June 30, 2019 , respectively. Accumulated amortization of the capitalized software costs is $22,472 and $24,568 as of December 31, 2018 and June 30, 2019 , respectively. The Company recorded amortization expense related to the capitalized software costs of $955 and $1,064 for the three months ended June 30, 2018 and 2019 , respectively, and $1,673 and $2,099 for the six months ended June 30, 2018 and 2019 , respectively. As of June 30, 2018 and 2019 , $1,536 and $817 , respectively, are included in “Accounts payable” and “Accrued liabilities,” which amounts are related to purchases of property and equipment. These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.

Accrued Liabilities

Accrued Liabilities	6 Months Ended
	Jun. 30, 2019
Payables and Accruals [Abstract]
Accrued Liabilities	Accrued Liabilities Accrued liabilities as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Accrued alternative fuels incentives $ 6,923 $ 6,212 Accrued employee benefits 2,248 3,009 Accrued interest 78 1,142 Accrued gas and equipment purchases 12,833 7,774 Accrued property and other taxes 3,397 4,605 Accrued salaries and wages 8,609 5,681 Other 14,381 11,340 Total accrued liabilities $ 48,469 $ 39,763

Debt

Debt	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Debt	Debt Debt obligations as of December 31, 2018 and June 30, 2019 consisted of the following and are further discussed below: December 31, 2018 Principal Balances Unamortized Debt Financing Costs Balance, Net of Financing Costs 7.5% Notes $ 50,000 $ 58 $ 49,942 NG Advantage debt 28,904 155 28,749 Other debt 1,024 — 1,024 Total debt 79,928 213 79,715 Less amounts due within one year (4,811 ) (99 ) (4,712 ) Total long-term debt $ 75,117 $ 114 $ 75,003 June 30, 2019 Principal Balances Unamortized Debt Financing Costs Balance Net of Financing Costs 7.5% Notes $ 50,000 $ 38 $ 49,962 NG Advantage debt 29,726 126 29,600 Other debt 912 — 912 Total debt 80,638 164 80,474 Less amounts due within one year (55,620 ) (58 ) (55,562 ) Total long-term debt $ 25,018 $ 106 $ 24,912 7.5% Notes In June 2013, the Company issued notes (the “ 7.5% Notes”) to T. Boone Pickens and Green Energy Investment Holdings, LLC (“GEIH”) in the amount of $150,000 . The 7.5% Notes bear interest at the rate of 7.5% per annum and are convertible at the option of the holder into shares of the Company’s common stock at a conversion price of $15.80 per share (the “ 7.5% Notes Conversion Price”). Upon written notice to the Company, each holder of a 7.5% Note has the right to exchange all or any portion of the principal and accrued and unpaid interest under its 7.5% Notes for shares of the Company’s common stock at the 7.5% Notes Conversion Price. Additionally, subject to certain restrictions, the Company can force conversion of each 7.5% Note into shares of its common stock if, following the second anniversary of the issuance of a 7.5% Note, such shares trade at a 40% premium to the 7.5% Notes Conversion Price for at least 20 trading days in any consecutive 30 trading day period. The entire principal balance of each 7.5% Note is due and payable seven years following its original issuance and the Company may repay each 7.5% Note at maturity in shares of its common stock (provided that the Company may not issue more than 13,993,630 shares of its common stock to holders of 7.5% Notes) or cash. All of the shares issuable upon conversion of the 7.5% Notes have been registered for resale by their holders pursuant to a registration statement that has been filed with and declared effective by the SEC. The 7.5% Notes include customary events of default which, if any of them occurs, would permit or require the principal of, and accrued interest on, the 7.5% Notes to become, or to be declared, due and payable. No events of default under the 7.5% Notes had occurred as of June 30, 2019 . Prior to January 1, 2018, (i) the Company purchased $25,000 of the 7.5% Notes from Mr. Pickens, (ii) Mr. Pickens transferred all remaining balance of his 7.5% Notes to third parties, and (iii) GEIH transferred $16,800 in principal amount of its 7.5% Notes to third parties. On June 29, 2018, and pursuant to the consent of the holders of the 7.5% Notes to the Company’s payments of amounts owed thereunder before maturity, the Company paid to the holders, in cash, an aggregate of $25,000 in principal amount and $505 in accrued and unpaid interest owed under all outstanding 7.5% Notes due July 2018. Upon such payment, the purchased 7.5% Notes were canceled in full. On December 4, 2018, the Company purchased from the holders thereof all outstanding 7.5% Notes due July 2019, having an aggregate outstanding principal amount of $50,000 , for a cash purchase price of $50,500 . Upon such purchase, the purchased 7.5% Notes were canceled in full. As a result of the foregoing transactions, as of June 30, 2019 , (i) GEIH held 7.5% Notes in an aggregate principal amount of $32,906 , and (ii) other third parties held 7.5% Notes in an aggregate principal amount of $17,094 , all of which are due June 2020. Plains Credit Facility On February 29, 2016, the Company entered into a Loan and Security Agreement (the “Plains LSA”) with PlainsCapital Bank (“Plains”), which, as amended on December 6, 2017, has a maturity date of September 30, 2019. Pursuant to the Plains LSA, Plains agreed to lend the Company up to $50,000 on a revolving basis from time to time (the “Credit Facility”). The Company had no amounts outstanding under the Credit Facility as of June 30, 2019 . Interest on the Plains Note is payable monthly and accrues at a rate equal to the greater of (i) the then-current LIBOR rate plus 2.30% or (ii) 2.70% . As collateral security for the prompt payment in full when due of the Company’s obligations to Plains under the Plains LSA and the Plains Note, the Company pledged to and granted Plains a security interest in all of its right, title and interest in the cash and corporate and municipal bonds that the Company holds in an account at Plains. There are certain covenants and events of default associated with the Plains LSA. No events of default under the Plains LSA had occurred as of June 30, 2019 . Société Générale Term Loan Facility On January 2, 2019, the Company entered into a term credit agreement (the “Credit Agreement”) with Société Générale, a company incorporated as a société anonyme under the laws of France (“SG”). The Credit Agreement provides for a term loan facility (the “SG Facility”) pursuant to which the Company may obtain, subject to certain conditions, up to $100,000 of loans (“Loans”) in support of its Zero Now truck financing program. Under the Credit Agreement, the Company is permitted to use the proceeds from the Loans solely to fund the incremental cost of trucks purchased or financed under the Zero Now truck financing program and related fees and expenses incurred by the Company in connection therewith. Interest on outstanding Loans accrues at a rate equal to LIBOR plus 1.30% per annum, and a commitment fee on any unused portion of the SG Facility accrues at a rate equal to 0.39% per annum. Interest and commitment fees are payable quarterly. The Credit Agreement does not include financial covenants, and the Company has not provided SG with any security for its obligations under the Credit Agreement. As described below, THUSA has entered into the Guaranty to guarantee the Company’s payment obligations to SG under the Credit Agreement. The Company has not drawn down on the SG Facility and no events of defaults had occurred as of June 30, 2019 . TOTAL Credit Support Agreement On January 2, 2019, the Company entered a credit support agreement (“CSA”) with Total Holdings USA Inc. (“THUSA”), a wholly owned subsidiary of TOTAL (as defined in Note 15 ). Under the CSA, THUSA agreed to enter into a guaranty agreement (“Guaranty”) pursuant to which it has guaranteed the Company’s obligation to repay to SG up to $100,000 in Loans and interest thereon in accordance with the Credit Agreement. In consideration for the commitments of THUSA under the CSA, the Company is required to pay THUSA a quarterly guaranty fee at a rate per quarter equal to 2.5% of the average aggregate Loan amount for the preceding calendar quarter. As security for the Company’s obligations under the CSA, on January 2, 2019, the Company entered into a pledge and security agreement with THUSA and delivered a collateral assignment of contracts to THUSA, pursuant to which the Company collaterally assigned to THUSA all fueling agreements it enters into with participants in the Zero Now truck financing program. In addition, on January 2, 2019, the Company entered into a lockbox agreement with THUSA and Plains, under which the Company granted THUSA a security interest in the cash flow generated by the fueling agreements the Company enters into with participants in the Zero Now truck financing program. The CSA will terminate following the later of: the payment in full of all of the Company’s obligations under the CSA; and the termination or expiration of the Guaranty following the maturity date of the last outstanding Loan or December 31, 2023, whichever is earlier. NG Advantage Debt On May 12, 2016 and January 24, 2017, respectively, NG Advantage entered into a Loan and Security Agreement (the “Commerce LSA”) with Commerce Bank & Trust Company (“Commerce”), pursuant to which Commerce agreed to lend NG Advantage $6,300 and $6,150 , respectively. The proceeds were primarily used to fund the purchases of CNG trailers and equipment. Interest and principal for both loans are payable monthly in 84 equal monthly installments at an annual rate of 4.41% and 5.0% , respectively. As collateral security for the prompt payment in full when due of NG Advantage’s obligations to Commerce under the Commerce LSA, NG Advantage pledged to and granted Commerce a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received under the Commerce LSA. On November 30, 2016, NG Advantage entered into a Loan and Security Agreement (the “Wintrust LSA”) with Wintrust Commercial Finance (“Wintrust”), pursuant to which Wintrust agreed to lend NG Advantage $4,695 . The proceeds were primarily used to fund the purchases of CNG trailers and equipment. Interest and principal is payable monthly in 72 equal monthly installments at an annual rate of 5.17% . As collateral security for the prompt payment in full when due of NG Advantage’s obligations to Wintrust under the Wintrust LSA, NG Advantage pledged to and granted Wintrust a security interest in all of its right, title and interest in the CNG trailers and equipment purchased with the proceeds received under the Wintrust LSA. Financing Obligations NG Advantage has entered into sale and leaseback transactions with various lessors as described below. In each instance, the sale and leaseback transaction does not qualify for sale-leaseback accounting because of NG Advantage’s continuing involvement with the buyer-lessor due to a fixed price repurchase option. As a result, the transactions are recorded under the financing method, in which the assets remain on the accompanying condensed consolidated balance sheets and the proceeds from the transactions are recorded as financing liabilities. On December 18, 2017, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “BoA MLA”) with Bank of America Leasing & Capital, LLC (“BoA”). Pursuant to the BoA MLA, NG Advantage received $2,117 in cash for CNG trailers and simultaneously leased them back from BoA for five years commencing January 1, 2018 with interest and principal payable in 60 equal monthly installments. On March 1, 2018, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “First National MLA”) with First National Capital, LLC (“First National”). Pursuant to the First National MLA, NG Advantage received $6,261 in cash, net of fees and the first month’s lease payment for CNG trailers and simultaneously leased them back from First National for six years commencing March 1, 2018 with interest and principal payable in 72 equal monthly installments. On December 20, 2018 (the “Closing Date”), NG Advantage entered into a purchase agreement to sell a compression station for a purchase price of $7,000 to an entity whose member owners are noncontrolling interest member owners of NG Advantage. On the Closing Date and immediately following the consummation of the sale of the compression station, NG Advantage entered into a lease agreement with the buyer of the station (the “Lease”) pursuant to which the station was leased back to NG Advantage for a term of five years with monthly rent payments equal to $70 . Of the purchase price, NG Advantage received $4,730 in cash, net of fees, the first month’s lease payment, and the repayment of a $2,000 promissory note from one of the member owners of the buyer, which was issued on November 19, 2018. On January 17, 2019, NG Advantage entered into a sale-leaseback arrangement through a Master Lease Agreement (the “Nations MLA”) with Nations Fund I, LLC (“Nations”). Pursuant to the Nations MLA, NG Advantage received $3,358 in cash, net of the first month’s lease payment, for CNG trailers and simultaneously leased them back from Nations for four years commencing February 1, 2019 with interest and principal payable in 48 equal monthly installments. Other Debt The Company has other debt due at various dates through 2023 bearing interest at rates up to 5.02% , with weighted -average interest rates of 4.78% and 4.78% as of December 31, 2018 and June 30, 2019 , respectively.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
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. The information required to compute basic and diluted net income (loss) per share is as follows: Three Months Ended Six Months Ended 2018 2019 2018 2019 Weighted-average common shares outstanding 162,613,316 204,653,723 157,432,786 204,426,459 Dilutive effect of potential common shares from restricted stock units and stock options — — 4,249,459 — Weighted-average common shares outstanding -diluted 162,613,316 204,653,723 161,682,245 204,426,459 The following potentially dilutive securities have been excluded from the diluted net income (loss) per share calculations because their effect would have been antidilutive. Although these securities were antidilutive for these periods, they could be dilutive in future periods. Three Months Ended Six Months Ended 2018 2019 2018 2019 Stock options 10,127,427 10,192,762 8,329,642 10,192,762 Convertible notes 13,409,242 3,164,557 13,409,242 3,164,557 Restricted stock units 2,451,674 1,289,751 2,451,674 1,289,751 Total 25,988,343 14,647,070 24,190,558 14,647,070

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation The following table summarizes the compensation expense and related income tax benefit related to the Company’s stock-based compensation arrangements recognized in the accompanying condensed consolidated statements of operations during the periods: Three Months Ended Six Months Ended 2018 2019 2018 2019 Stock-based compensation expense, net of $0 tax in 2018 and 2019 $ 1,208 $ 918 $ 3,106 $ 2,164 As of June 30, 2019 , there was $4,643 of total unrecognized compensation costs related to unvested shares subject to outstanding stock options and restricted stock units, which is expected to be expensed over a weighted-average period of approximately 1.74 years .

Stockholders_ Equity

Stockholders’ Equity	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Stockholders’ Equity	Stockholders ’ Equity Issuance of Common Stock On May 9, 2018, the Company entered into a stock purchase agreement (the “Purchase Agreement”) with Total Marketing Services, S.A., a wholly owned subsidiary of Total S.A. (“Total”). Pursuant to the Purchase Agreement, the Company agreed to sell and issue, and Total agreed to purchase, up to 50,856,296 shares of the Company’s common stock at a purchase price of $1.64 per share, in a private placement (the “Total Private Placement”). The purchase price per share was the volume-weighted average price for the Company’s common stock between March 23, 2018 (the day on which discussions began between the Company and Total) and May 3, 2018 (the day on which the Company agreed in principle with Total regarding the structure and basic terms of its investment). As of the date of the Purchase Agreement, Total did not hold or otherwise beneficially own any shares of the Company’s common stock, and Total has agreed, until the later of May 9, 2020 or such date when it ceases to hold more than 5.0% of the Company’s common stock then outstanding, among other similar undertakings and subject to customary conditions and exceptions, to not purchase shares of the Company’s common stock or otherwise pursue transactions that would result in Total beneficially owning more than 30.0% of the Company’s equity securities without the approval of the Company’s board of directors. On June 13, 2018, the Company and Total closed the Total Private Placement, in which: (1) the Company issued to Total all of the 50,856,296 shares of its common stock issuable under the Purchase Agreement, resulting in Total holding approximately 25.0% of the outstanding shares of the Company’s common stock and the largest ownership position of the Company as of June 30, 2019 ; (2) Total paid to the Company an aggregate of $83,404 in gross proceeds, which the Company has used and expects to continue to use for working capital and general corporate purposes, which may include executing its business plans, pursuing opportunities for further growth, and retiring a portion of its outstanding indebtedness; and (3) the Company and Total entered into a registration rights agreement, described below. In connection with the issuance of common stock, the Company incurred transaction fees of $1,909 . Pursuant to the Purchase Agreement, the Company and Total also entered into a registration rights agreement on June 13, 2018, upon the closing under the Purchase Agreement. Pursuant to the registration rights agreement, the Company filed a registration statement with the SEC to cover the resale of the shares issued and sold under the Purchase Agreement, which was declared effective on August 16, 2018, and is obligated to use its commercially reasonable efforts to maintain the effectiveness of such registration statement until all such shares are sold or may be sold without restriction under Rule 144 under the Securities Act of 1933, as amended. As of June 30, 2019 , the Company was in compliance with all of its registration covenants set forth in the registration rights agreement.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for interim periods is determined using an estimate of the Company’s annual effective tax rate, adjusted for discrete items, if any, that are taken into account in the relevant period. Each quarter, the Company updates the estimate of the annual effective tax rate, and if the estimated tax rate changes, a cumulative adjustment is recorded. The Company’s income tax expense was $ 89 and $66 for the three months ended June 30, 2018 and 2019 , respectively and $177 and $126 for the six months ended June 30, 2018 and 2019 , respectively. Tax expense for all periods was comprised of taxes due on the Company’s U.S. and foreign operations. The decrease in the Company’s income tax expense for the three and six months ended June 30, 2019 as compared to the three and six months ended June 30, 2018 was primarily due to a reduction in the Company’s expected state tax expense. The effective tax rates for the three and six months ended June 30, 2018 and 2019 are different from the federal statutory tax rate primarily due to losses for which no tax benefit has been recognized. The Company increased its liability for unrecognized tax benefits in the six months ended June 30, 2018 by $ 2,689 . This increase is the portion of AFTC revenue recognized in the period attributed to the federal fuel tax the Company collected from its customers during the year ended December 31, 2017. The net interest incurred was immaterial for both the three and six months ended June 30, 2018 and 2019 , respectively.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Environmental Matters The Company is subject to federal, state, local and foreign environmental laws and regulations. The Company does not anticipate any expenditures to comply with such laws and regulations that would have a material impact on the Company’s consolidated financial position, results of operations or liquidity. The Company believes that its operations comply, in all material respects, with applicable federal, state, local and foreign environmental laws and regulations. Litigation, Claims and Contingencies The Company may become party to various legal actions that arise in the ordinary course of its business. The Company is also subject to audit by tax and other authorities for varying periods in various federal, state, local and foreign jurisdictions, and disputes may arise during the course of these audits. It is impossible to determine the ultimate liabilities that the Company may incur resulting from any of these lawsuits, claims, proceedings, audits, commitments, contingencies and related matters or the timing of these liabilities, if any. If these matters were to ultimately be resolved unfavorably, it is possible that such an outcome could have a material adverse effect upon the Company’s consolidated financial position, results of operations, or liquidity. The Company does not, however, anticipate such an outcome and it believes the ultimate resolution of these matters will not have a material adverse effect on the Company’s consolidated financial position, results of operations, or liquidity.

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases	Leases Leases (Topic 842) On January 1, 2019, the Company adopted the new lease accounting standard (see Note 20 for more information on the standard and the impact of the adoption) where leases are now classified as either operating leases or finance leases. The Company’s operating leases are comprised of real estate for fueling stations, office spaces, warehouses, a LNG liquefaction plant, and office equipment, and its finance leases are comprised of vehicles. At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether it obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether it has the right to direct the use of the asset. The commencement date of the contract is when the lessor makes the underlying asset available for use by the lessee. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made, and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less. As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease. The lease classification affects the expense recognition on the condensed consolidated statement of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, where depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting. The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12 . NG Advantage has provided residual value guarantees on leases of certain vehicles aggregating $1,381 to the lessors. NG Advantage expects to owe these amounts in full and therefore they have been included in the measurement of the lease liabilities and ROU assets. Certain of the Company’s real estate leases contain variable lease payments, including payments based on a change in the index or gasoline gallon equivalents of natural gas dispensed at fueling stations. These variable lease payments cannot be determined at the commencement of the lease, are not included in the ROU assets and liabilities and are recorded as a period expense when incurred. Lessee Accounting As of June 30, 2019 , the Company’s finance and operating lease asset and liability balances were as follows: June 30, 2019 Finance leases: Land, property and equipment, gross $ 5,917 Accumulated depreciation (1,927 ) Land, property and equipment, net $ 3,990 Current portion of finance lease obligations $ 654 Long-term portion of finance lease obligations 3,236 Total finance lease liabilities $ 3,890 Operating leases: Operating lease right-of-use assets (1) $ 24,490 Current portion of operating lease obligations $ 3,570 Long-term portion of operating lease obligations 22,245 Total operating lease liabilities $ 25,815 (1) The Company’s operating lease ROU assets are comprised of the following: June 30, 2019 Assets Liabilities Real estate for fueling stations $ 18,432 $ 18,432 LNG plant, office spaces and warehouses 6,048 7,373 Office equipment 10 10 Total operating lease right-of-use assets $ 24,490 $ 25,815 The components of lease expense for finance and operating leases consisted of the following: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Finance leases: Depreciation on assets under finance leases $ 105 $ 364 Interest on lease liabilities 50 99 Total finance leases expense $ 155 $ 463 Operating leases: Lease expense $ 1,618 $ 3,101 Lease expense on short-term leases 485 1,587 Variable lease expense 699 1,330 Sublease income (52 ) (103 ) Total operating leases expense $ 2,750 $ 5,915 Supplemental information on finance and operating leases are as follows: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating cash outflows from finance leases $ (49 ) $ (98 ) Operating cash outflows from operating leases $ (710 ) $ (1,860 ) Financing cash outflows from finance leases $ (665 ) $ (849 ) Assets obtained in exchange for new finance lease liabilities (1) $ 134 $ 263 ROU assets obtained in exchange for new operating lease liabilities (1) $ 1,732 $ 1,732 June 30, 2019 Weighted-average remaining lease term - finance leases 4.91 years Weighted-average remaining lease term - operating leases 11.24 years Weighted-average discount rate - finance leases 4.72% Weighted-average discount rate - operating leases 8.20% (1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities. The following schedule represents the Company’s maturities of finance and operating lease liabilities as of June 30, 2019 : Finance Leases Operating Leases Fiscal year: 2019 $ 437 $ 2,808 2020 752 4,627 2021 662 3,720 2022 555 2,809 2023 479 2,807 Thereafter 1,610 24,242 Total minimum lease payments 4,495 41,013 Less amount representing interest (605 ) (15,198 ) Present value of lease liabilities $ 3,890 $ 25,815 Lessor Accounting The Company leases fueling station equipment to customers that contain an option to extend and an end-of-term purchase option. Receivables from these leases are accounted for as finance leases, specifically sales-type leases, and are included in “Other receivables” and “Notes receivable and other long-term assets, net” in the condensed consolidated balance sheets. The Company recognizes the net investment in the lease as the sum of the lease receivable and the unguaranteed residual value, both of which are measured at the present value using the interest rate implicit in the lease. During the three and six months ended June 30, 2019 , the Company recognized $37 and $73 , respectively, in “Interest income” on its lease receivables. The following schedule represents the Company’s maturities of lease receivables as of June 30, 2019 : Fiscal year: 2019 $ 93 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Total minimum lease payments 2,077 Less amount representing interest (1,007 ) Present value of lease receivables $ 1,070 Leases (Topic 840) As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption. Operating Lease Commitments The Company leases facilities, including the land for its LNG production plant in Boron, California and certain equipment under noncancelable operating leases expiring at various dates through 2038. If a lease has a fixed and determinable escalation clause, or periods of rent holidays, the difference between rental expense and rent paid is included in “Accrued liabilities” and “Other long-term liabilities” in the accompanying consolidated balance sheets. The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018 : Fiscal year: 2019 $ 6,340 2020 4,332 2021 3,311 2022 2,409 2023 2,300 Thereafter 13,214 Total future minimum lease payments $ 31,906 Rent expense totaled $1,698 and $3,225 for the three and six months ended June 30, 2018 , respectively. Capital Lease Obligations and Receivables The Company leases equipment under capital leases with a weighted-average interest rate of 4.48% . As of December 31, 2018 , future payments under these capital leases are as follows: Fiscal year: 2019 $ 883 2020 742 2021 656 2022 540 2023 529 Thereafter 1,868 Total minimum lease payments 5,218 Less amount representing interest (749 ) Capital lease obligations 4,469 Less current portion (693 ) Capital lease obligations, less current portion $ 3,776 The value of the equipment under capital leases as of December 31, 2018 was $6,143 , with related accumulated amortization of $1,832 , respectively. The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5% . As of December 31, 2018 , future receipts under this lease are as follows: Fiscal year: 2019 $ 186 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Capital lease receivables 2,170 Less amount representing interest (1,080 ) Capital lease receivables, less current portion $ 1,090
Leases	Leases Leases (Topic 842) On January 1, 2019, the Company adopted the new lease accounting standard (see Note 20 for more information on the standard and the impact of the adoption) where leases are now classified as either operating leases or finance leases. The Company’s operating leases are comprised of real estate for fueling stations, office spaces, warehouses, a LNG liquefaction plant, and office equipment, and its finance leases are comprised of vehicles. At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether it obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether it has the right to direct the use of the asset. The commencement date of the contract is when the lessor makes the underlying asset available for use by the lessee. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made, and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less. As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease. The lease classification affects the expense recognition on the condensed consolidated statement of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, where depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting. The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12 . NG Advantage has provided residual value guarantees on leases of certain vehicles aggregating $1,381 to the lessors. NG Advantage expects to owe these amounts in full and therefore they have been included in the measurement of the lease liabilities and ROU assets. Certain of the Company’s real estate leases contain variable lease payments, including payments based on a change in the index or gasoline gallon equivalents of natural gas dispensed at fueling stations. These variable lease payments cannot be determined at the commencement of the lease, are not included in the ROU assets and liabilities and are recorded as a period expense when incurred. Lessee Accounting As of June 30, 2019 , the Company’s finance and operating lease asset and liability balances were as follows: June 30, 2019 Finance leases: Land, property and equipment, gross $ 5,917 Accumulated depreciation (1,927 ) Land, property and equipment, net $ 3,990 Current portion of finance lease obligations $ 654 Long-term portion of finance lease obligations 3,236 Total finance lease liabilities $ 3,890 Operating leases: Operating lease right-of-use assets (1) $ 24,490 Current portion of operating lease obligations $ 3,570 Long-term portion of operating lease obligations 22,245 Total operating lease liabilities $ 25,815 (1) The Company’s operating lease ROU assets are comprised of the following: June 30, 2019 Assets Liabilities Real estate for fueling stations $ 18,432 $ 18,432 LNG plant, office spaces and warehouses 6,048 7,373 Office equipment 10 10 Total operating lease right-of-use assets $ 24,490 $ 25,815 The components of lease expense for finance and operating leases consisted of the following: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Finance leases: Depreciation on assets under finance leases $ 105 $ 364 Interest on lease liabilities 50 99 Total finance leases expense $ 155 $ 463 Operating leases: Lease expense $ 1,618 $ 3,101 Lease expense on short-term leases 485 1,587 Variable lease expense 699 1,330 Sublease income (52 ) (103 ) Total operating leases expense $ 2,750 $ 5,915 Supplemental information on finance and operating leases are as follows: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating cash outflows from finance leases $ (49 ) $ (98 ) Operating cash outflows from operating leases $ (710 ) $ (1,860 ) Financing cash outflows from finance leases $ (665 ) $ (849 ) Assets obtained in exchange for new finance lease liabilities (1) $ 134 $ 263 ROU assets obtained in exchange for new operating lease liabilities (1) $ 1,732 $ 1,732 June 30, 2019 Weighted-average remaining lease term - finance leases 4.91 years Weighted-average remaining lease term - operating leases 11.24 years Weighted-average discount rate - finance leases 4.72% Weighted-average discount rate - operating leases 8.20% (1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities. The following schedule represents the Company’s maturities of finance and operating lease liabilities as of June 30, 2019 : Finance Leases Operating Leases Fiscal year: 2019 $ 437 $ 2,808 2020 752 4,627 2021 662 3,720 2022 555 2,809 2023 479 2,807 Thereafter 1,610 24,242 Total minimum lease payments 4,495 41,013 Less amount representing interest (605 ) (15,198 ) Present value of lease liabilities $ 3,890 $ 25,815 Lessor Accounting The Company leases fueling station equipment to customers that contain an option to extend and an end-of-term purchase option. Receivables from these leases are accounted for as finance leases, specifically sales-type leases, and are included in “Other receivables” and “Notes receivable and other long-term assets, net” in the condensed consolidated balance sheets. The Company recognizes the net investment in the lease as the sum of the lease receivable and the unguaranteed residual value, both of which are measured at the present value using the interest rate implicit in the lease. During the three and six months ended June 30, 2019 , the Company recognized $37 and $73 , respectively, in “Interest income” on its lease receivables. The following schedule represents the Company’s maturities of lease receivables as of June 30, 2019 : Fiscal year: 2019 $ 93 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Total minimum lease payments 2,077 Less amount representing interest (1,007 ) Present value of lease receivables $ 1,070 Leases (Topic 840) As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption. Operating Lease Commitments The Company leases facilities, including the land for its LNG production plant in Boron, California and certain equipment under noncancelable operating leases expiring at various dates through 2038. If a lease has a fixed and determinable escalation clause, or periods of rent holidays, the difference between rental expense and rent paid is included in “Accrued liabilities” and “Other long-term liabilities” in the accompanying consolidated balance sheets. The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018 : Fiscal year: 2019 $ 6,340 2020 4,332 2021 3,311 2022 2,409 2023 2,300 Thereafter 13,214 Total future minimum lease payments $ 31,906 Rent expense totaled $1,698 and $3,225 for the three and six months ended June 30, 2018 , respectively. Capital Lease Obligations and Receivables The Company leases equipment under capital leases with a weighted-average interest rate of 4.48% . As of December 31, 2018 , future payments under these capital leases are as follows: Fiscal year: 2019 $ 883 2020 742 2021 656 2022 540 2023 529 Thereafter 1,868 Total minimum lease payments 5,218 Less amount representing interest (749 ) Capital lease obligations 4,469 Less current portion (693 ) Capital lease obligations, less current portion $ 3,776 The value of the equipment under capital leases as of December 31, 2018 was $6,143 , with related accumulated amortization of $1,832 , respectively. The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5% . As of December 31, 2018 , future receipts under this lease are as follows: Fiscal year: 2019 $ 186 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Capital lease receivables 2,170 Less amount representing interest (1,080 ) Capital lease receivables, less current portion $ 1,090
Leases	Leases Leases (Topic 842) On January 1, 2019, the Company adopted the new lease accounting standard (see Note 20 for more information on the standard and the impact of the adoption) where leases are now classified as either operating leases or finance leases. The Company’s operating leases are comprised of real estate for fueling stations, office spaces, warehouses, a LNG liquefaction plant, and office equipment, and its finance leases are comprised of vehicles. At the inception of a contract the Company assesses whether the contract is, or contains, a lease. The Company’s assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether it obtains the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether it has the right to direct the use of the asset. The commencement date of the contract is when the lessor makes the underlying asset available for use by the lessee. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset during the lease term and lease liabilities represent obligations to make lease payments arising from the lease. ROU assets and liabilities are recognized at the commencement date based on the net present value of fixed lease payments over the lease term. ROU assets also include any initial direct costs and advance lease payments made, and exclude lease incentives. Lease liabilities also include terminal purchase options when deemed reasonably certain to exercise. The Company’s lease term includes options to extend when it is reasonably certain that it will exercise that option. The Company has elected not to recognize ROU assets and lease liabilities for short-term leases that have a term of 12 months or less. As most of the Company’s operating leases do not have an implicit rate that can be readily determined, the Company uses its secured incremental borrowing rate for the same term as the underlying lease based on information available at lease commencement. For finance leases, the Company uses the rate implicit in the lease. The lease classification affects the expense recognition on the condensed consolidated statement of operations. Operating lease charges are recorded in “Cost of sales, exclusive of depreciation and amortization,” and “Selling, general and administrative” expense. Finance lease charges are split, where depreciation on assets under finance leases is recorded in “Depreciation and amortization” expense and an implied interest component is recorded in “Interest expense.” The expense recognition for operating leases and finance leases is substantially consistent with legacy accounting. The Company leases an office space from T. Boone Pickens in Dallas, TX. The lease, which expires in October 2019, calls for monthly rental payments of $12 . NG Advantage has provided residual value guarantees on leases of certain vehicles aggregating $1,381 to the lessors. NG Advantage expects to owe these amounts in full and therefore they have been included in the measurement of the lease liabilities and ROU assets. Certain of the Company’s real estate leases contain variable lease payments, including payments based on a change in the index or gasoline gallon equivalents of natural gas dispensed at fueling stations. These variable lease payments cannot be determined at the commencement of the lease, are not included in the ROU assets and liabilities and are recorded as a period expense when incurred. Lessee Accounting As of June 30, 2019 , the Company’s finance and operating lease asset and liability balances were as follows: June 30, 2019 Finance leases: Land, property and equipment, gross $ 5,917 Accumulated depreciation (1,927 ) Land, property and equipment, net $ 3,990 Current portion of finance lease obligations $ 654 Long-term portion of finance lease obligations 3,236 Total finance lease liabilities $ 3,890 Operating leases: Operating lease right-of-use assets (1) $ 24,490 Current portion of operating lease obligations $ 3,570 Long-term portion of operating lease obligations 22,245 Total operating lease liabilities $ 25,815 (1) The Company’s operating lease ROU assets are comprised of the following: June 30, 2019 Assets Liabilities Real estate for fueling stations $ 18,432 $ 18,432 LNG plant, office spaces and warehouses 6,048 7,373 Office equipment 10 10 Total operating lease right-of-use assets $ 24,490 $ 25,815 The components of lease expense for finance and operating leases consisted of the following: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Finance leases: Depreciation on assets under finance leases $ 105 $ 364 Interest on lease liabilities 50 99 Total finance leases expense $ 155 $ 463 Operating leases: Lease expense $ 1,618 $ 3,101 Lease expense on short-term leases 485 1,587 Variable lease expense 699 1,330 Sublease income (52 ) (103 ) Total operating leases expense $ 2,750 $ 5,915 Supplemental information on finance and operating leases are as follows: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating cash outflows from finance leases $ (49 ) $ (98 ) Operating cash outflows from operating leases $ (710 ) $ (1,860 ) Financing cash outflows from finance leases $ (665 ) $ (849 ) Assets obtained in exchange for new finance lease liabilities (1) $ 134 $ 263 ROU assets obtained in exchange for new operating lease liabilities (1) $ 1,732 $ 1,732 June 30, 2019 Weighted-average remaining lease term - finance leases 4.91 years Weighted-average remaining lease term - operating leases 11.24 years Weighted-average discount rate - finance leases 4.72% Weighted-average discount rate - operating leases 8.20% (1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities. The following schedule represents the Company’s maturities of finance and operating lease liabilities as of June 30, 2019 : Finance Leases Operating Leases Fiscal year: 2019 $ 437 $ 2,808 2020 752 4,627 2021 662 3,720 2022 555 2,809 2023 479 2,807 Thereafter 1,610 24,242 Total minimum lease payments 4,495 41,013 Less amount representing interest (605 ) (15,198 ) Present value of lease liabilities $ 3,890 $ 25,815 Lessor Accounting The Company leases fueling station equipment to customers that contain an option to extend and an end-of-term purchase option. Receivables from these leases are accounted for as finance leases, specifically sales-type leases, and are included in “Other receivables” and “Notes receivable and other long-term assets, net” in the condensed consolidated balance sheets. The Company recognizes the net investment in the lease as the sum of the lease receivable and the unguaranteed residual value, both of which are measured at the present value using the interest rate implicit in the lease. During the three and six months ended June 30, 2019 , the Company recognized $37 and $73 , respectively, in “Interest income” on its lease receivables. The following schedule represents the Company’s maturities of lease receivables as of June 30, 2019 : Fiscal year: 2019 $ 93 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Total minimum lease payments 2,077 Less amount representing interest (1,007 ) Present value of lease receivables $ 1,070 Leases (Topic 840) As required by the new lease accounting standard, legacy disclosures are provided for periods prior to adoption. Operating Lease Commitments The Company leases facilities, including the land for its LNG production plant in Boron, California and certain equipment under noncancelable operating leases expiring at various dates through 2038. If a lease has a fixed and determinable escalation clause, or periods of rent holidays, the difference between rental expense and rent paid is included in “Accrued liabilities” and “Other long-term liabilities” in the accompanying consolidated balance sheets. The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018 : Fiscal year: 2019 $ 6,340 2020 4,332 2021 3,311 2022 2,409 2023 2,300 Thereafter 13,214 Total future minimum lease payments $ 31,906 Rent expense totaled $1,698 and $3,225 for the three and six months ended June 30, 2018 , respectively. Capital Lease Obligations and Receivables The Company leases equipment under capital leases with a weighted-average interest rate of 4.48% . As of December 31, 2018 , future payments under these capital leases are as follows: Fiscal year: 2019 $ 883 2020 742 2021 656 2022 540 2023 529 Thereafter 1,868 Total minimum lease payments 5,218 Less amount representing interest (749 ) Capital lease obligations 4,469 Less current portion (693 ) Capital lease obligations, less current portion $ 3,776 The value of the equipment under capital leases as of December 31, 2018 was $6,143 , with related accumulated amortization of $1,832 , respectively. The Company also leases fueling station equipment to customers under sales-type leases with a weighted-average interest rate of 13.5% . As of December 31, 2018 , future receipts under this lease are as follows: Fiscal year: 2019 $ 186 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Capital lease receivables 2,170 Less amount representing interest (1,080 ) Capital lease receivables, less current portion $ 1,090

Alternative Fuels Excise Tax Cr

Alternative Fuels Excise Tax Credit	6 Months Ended
	Jun. 30, 2019
Alternative Fuels Excise Tax Credit
Alternative Fuels Excise Tax Credit	Alternative Fuels Excise Tax Credit Under separate pieces of U.S. federal legislation, the Company has been eligible to receive the AFTC tax credit for its natural gas vehicle fuel sales made between October 1, 2006 and December 31, 2017. The AFTC, which had previously expired on December 31, 2016, was reinstated on February 9, 2018 to apply to vehicle fuel sales made from January 1, 2017 through December 31, 2017. The AFTC credit is equal to $0.50 per gasoline gallon equivalent of CNG that the Company sold as vehicle fuel and $0.50 per diesel gallon of LNG that the Company sold as vehicle fuel in 2016 and 2017. Based on the service relationship with its customers, either the Company or its customers claims the credit. The Company records its AFTC credits, if any, as revenue in its consolidated statements of operations because the credits are fully payable to the Company and do not offset income tax liabilities. As such, the credits are not deemed income tax credits under the accounting guidance applicable to income taxes. As a result of the most recent legislation authorizing AFTC being signed into law on February 9, 2018, all AFTC revenue for vehicle fuel the Company sold in the 2017 calendar year, totaling $25,481 , has been recognized during the three months ended March 31, 2018 and was collected subsequent to that date. In addition, during the three months ended June 30, 2018, the Internal Revenue Service approved, and the Company recognized as revenue, $1,382 of AFTC credit claims related to prior years. AFTC is not currently available, and may not be reinstated, for vehicle fuel sales made after December 31, 2017.

Recently Adopted Accounting Cha

Recently Adopted Accounting Changes	6 Months Ended
	Jun. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Adopted Accounting Changes	Recently Adopted Accounting Changes In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASC 842”), which amends the guidance in former Accounting Standards Codification Topic 840, Leases (“ASC 840”). The new standard requires most leases to be recognized on the balance sheet which will increase reported assets and liabilities. Accounting for lessors and capital leases (now known as finance leases) is substantially similar to ASC 840. The new standard is effective for annual and interim periods in fiscal years beginning after December 15, 2018, which for the Company is the first quarter of 2019. The Company adopted this standard using the modified retrospective method and recognized the cumulative effect of initially applying ASC 842 as an adjustment to accumulated deficit in the consolidated balance sheet as of January 1, 2019. Results for reporting periods beginning after January 1, 2019 are presented under ASC 842, while prior period amounts are not adjusted. This adoption had a material impact to the Company’s condensed consolidated balance sheets and did not have a material impact to the Company’s condensed consolidated statements of operations or its condensed consolidated statements of cash flows. The primary impact was to record ROU assets and lease liabilities for existing operating leases on the condensed consolidated balance sheets. As permitted under ASC 842, the Company elected the package of practical expedients that permit it to not reassess (1) whether an existing contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. The Company also elected the practical expedient allowing it to use hindsight in determining the lease term and in assessing the likelihood a purchase option will be exercised. The ASC 842 adoption adjustments are as follows: Balance as of December 31, 2018 Adjustments Due to ASC 842 Balance as of January 1, 2019 Operating lease right-of-use assets $ — $ 24,453 $ 24,453 Operating lease obligations $ — $ 25,943 $ 25,943 Accrued liabilities $ 48,469 $ (496 ) $ 47,973 Other long-term liabilities $ 15,035 $ (994 ) $ 14,041 The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of June 30, 2019 are as follows: June 30, 2019 Balance before ASC 842 Adoption Effect of Change As Reported Operating lease right-of-use assets $ — $ 24,490 $ 24,490 Current portion of operating lease obligations $ — $ 3,570 $ 3,570 Long-term portion of operating lease obligations $ — $ 22,245 $ 22,245 Accrued liabilities $ 40,294 $ (531 ) $ 39,763 Other long-term liabilities $ 13,611 $ (710 ) $ 12,901

General (Policies)

General (Policies)	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements include the accounts of the Company and its subsidiaries, and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to state fairly the Company’s consolidated financial position as of June 30, 2019 , and results of operations, comprehensive income (loss) and cash flows for the three and six months ended June 30, 2018 and 2019 . All intercompany accounts and transactions have been eliminated in consolidation. The results of operations for the three and six month periods ended June 30, 2018 and 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any future year. Certain information and disclosures normally included in the notes to consolidated financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”), but the resultant disclosures contained herein are in accordance with accounting principles generally accepted in the United States of America (“US GAAP”) as they apply to interim reporting. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements as of and for the year ended December 31, 2018 that are included in the Company’s Annual Report on Form 10-K filed with the SEC on March 12, 2019.
Reclassifications	Reclassifications Certain prior period amounts have been reclassified in the condensed consolidated balance sheets and condensed consolidated statements of operations and cash flows to conform to the current period presentation. These reclassifications had no material impact on the Company’s consolidated financial position, results of operations, or cash flows as previously reported.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the amounts reported in the accompanying condensed consolidated financial statements and these notes. Actual results could differ from those estimates and may result in material effects on the Company’s operating results and financial position. Significant estimates made in preparing the accompanying condensed consolidated financial statements include (but are not limited to) those related to revenue recognition, fair value measurements, goodwill and long-lived asset valuations and impairment assessments, income tax valuations and stock-based compensation expense.
Revenue Recognition Overview	Revenue Recognition Overview The Company recognizes revenue when control of the promised goods or services is transferred to its customers, in an amount that reflects the consideration to which it expects to be entitled in exchange for the goods or services. To achieve that core principle, a five-step approach is applied: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue allocated to each performance obligation when the Company satisfies the performance obligation. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer, and is the unit of account for revenue recognition. The table below presents the Company’s revenue disaggregated by revenue source. The Company is generally the principal in its customer contracts because it has control over the goods and services prior to them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities. Three Months Ended Six Months Ended 2018 2019 2018 2019 Volume -related (1) $ 62,642 $ 66,260 $ 129,978 $ 140,788 Station construction sales 5,781 5,943 11,579 9,113 Alternative fuels excise tax credit (“AFTC”) 1,382 — 26,863 — Other 662 115 4,450 115 Total revenue $ 70,467 $ 72,318 $ 172,870 $ 150,016 (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. The amounts are classified as revenue because the Company’s commodity swap contracts are used to economically offset the risk associated with the diesel -to -natural gas price spread resulting from anticipated customer fueling contracts under the Company’s Zero Now truck financing program. See Note 6 for more information about these derivative instruments. For the three and six months ended June 30, 2019 , changes in the fair value of commodity swaps and customer fueling contracts amounted to a gain of $565 and a loss of $ 4,395 , respectively. Remaining Performance Obligations Remaining performance obligations represent the transaction price of customer orders for which the work has not been performed. As of June 30, 2019 , the aggregate amount of the transaction price allocated to remaining performance obligations was $10,825 which related to the Company’s station construction sale contracts. The Company expects to recognize revenue on the remaining performance obligations under these contracts over the next 12 to 24 months. For volume -related revenue, the Company has elected to apply an optional exemption, which waives the requirement to disclose the remaining performance obligation for revenue recognized through the ‘ right to invoice’ practical expedient. Contract Balances The timing of revenue recognition, billings and cash collections results in billed accounts receivable, unbilled receivables (contract assets), and customer advances and deposits (contract liabilities) in the accompanying condensed consolidated balance sheets. Changes in the contract asset and liability balances during the six months ended June 30, 2019 , were not materially impacted by any factors outside the normal course of business. As of December 31, 2018 and June 30, 2019 , the Company’s contract balances were as follows: December 31, 2018 June 30, 2019 Receivables, net $ 68,865 $ 60,567 Contract Assets - Current $ 656 $ 893 Contract Assets - Noncurrent 3,825 3,654 Contract Assets - Total $ 4,481 $ 4,547 Contract Liabilities - Current $ 5,513 $ 4,896 Contract Liabilities - Noncurrent 9,844 7,044 Contract Liabilities - Total $ 15,357 $ 11,940 Receivables, Net “Receivables, net” in the accompanying condensed consolidated balance sheets include amounts billed and currently due from customers. The amounts due are stated at their net estimated realizable value. The Company maintains an allowance for doubtful accounts to provide for the estimated amount of receivables that will not be collected. The allowance is based upon an assessment of customer creditworthiness, historical payment experience, and the age of outstanding receivables. Contract Assets Contract assets include unbilled amounts typically resulting from the Company’s station construction sale contracts, when the cost-to-cost method of revenue recognition is utilized and revenue recognized exceeds the amount billed to the customer, and right to payment is not just subject to the passage of time. Amounts may not exceed their net realizable value. Contract assets are classified as current or noncurrent based on the timing of billings. The current portion is included in “Prepaid expenses and other current assets” and the noncurrent portion is included in “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets. Contract Liabilities Contract liabilities consist of billings in excess of revenue recognized from the Company’s station construction sale contracts and payments received primarily from a customer of NG Advantage, LLC (“NG Advantage”) in advance of the performance obligations. Deferred revenue is classified as current or noncurrent based on when the revenue is expected to be recognized. The current portion and noncurrent portion of deferred revenue are included in “Deferred revenue” and “Other long -term liabilities,” respectively, in the accompanying condensed consolidated balance sheets.
Recently Adopted Accounting Changes and Recently Issued Accounting Standards	s In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASC 842”), which amends the guidance in former Accounting Standards Codification Topic 840, Leases (“ASC 840”). The new standard requires most leases to be recognized on the balance sheet which will increase reported assets and liabilities. Accounting for lessors and capital leases (now known as finance leases) is substantially similar to ASC 840. The new standard is effective for annual and interim periods in fiscal years beginning after December 15, 2018, which for the Company is the first quarter of 2019. The Company adopted this standard using the modified retrospective method and recognized the cumulative effect of initially applying ASC 842 as an adjustment to accumulated deficit in the consolidated balance sheet as of January 1, 2019. Results for reporting periods beginning after January 1, 2019 are presented under ASC 842, while prior period amounts are not adjusted. This adoption had a material impact to the Company’s condensed consolidated balance sheets and did not have a material impact to the Company’s condensed consolidated statements of operations or its condensed consolidated statements of cash flows. The primary impact was to record ROU assets and lease liabilities for existing operating leases on the condensed consolidated balance sheets. As permitted under ASC 842, the Company elected the package of practical expedients that permit it to not reassess (1) whether an existing contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. The Company also elected the practical expedient allowing it to use hindsight in determining the lease term and in assessing the likelihood a purchase option will be exercised. The ASC 842 adoption adjustments are as follows: Balance as of December 31, 2018 Adjustments Due to ASC 842 Balance as of January 1, 2019 Operating lease right-of-use assets $ — $ 24,453 $ 24,453 Operating lease obligations $ — $ 25,943 $ 25,943 Accrued liabilities $ 48,469 $ (496 ) $ 47,973 Other long-term liabilities $ 15,035 $ (994 ) $ 14,041 The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of June 30, 2019 are as follows: June 30, 2019 Balance before ASC 842 Adoption Effect of Change As Reported Operating lease right-of-use assets $ — $ 24,490 $ 24,490 Current portion of operating lease obligations $ — $ 3,570 $ 3,570 Long-term portion of operating lease obligations $ — $ 22,245 $ 22,245 Accrued liabilities $ 40,294 $ (531 ) $ 39,763 Other long-term liabilities $ 13,611 $ (710 ) $ 12,901

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	6 Months Ended
	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of revenue	The table below presents the Company’s revenue disaggregated by revenue source. The Company is generally the principal in its customer contracts because it has control over the goods and services prior to them being transferred to the customer, and as such, revenue is recognized on a gross basis. Sales and usage-based taxes are excluded from revenues. Revenue is recognized net of allowances for returns and any taxes collected from customers, which are subsequently remitted to governmental authorities. Three Months Ended Six Months Ended 2018 2019 2018 2019 Volume -related (1) $ 62,642 $ 66,260 $ 129,978 $ 140,788 Station construction sales 5,781 5,943 11,579 9,113 Alternative fuels excise tax credit (“AFTC”) 1,382 — 26,863 — Other 662 115 4,450 115 Total revenue $ 70,467 $ 72,318 $ 172,870 $ 150,016 (1) Includes changes in fair value of derivative instruments related to the Company’s commodity swap and customer fueling contracts. The amounts are classified as revenue because the Company’s commodity swap contracts are used to economically offset the risk associated with the diesel -to -natural gas price spread resulting from anticipated customer fueling contracts under the Company’s Zero Now truck financing program. See Note 6 for more information about these derivative instruments. For the three and six months ended June 30, 2019 , changes in the fair value of commodity swaps and customer fueling contracts amounted to a gain of $565 and a loss of $ 4,395 , respectively.
Summary of contract balances	As of December 31, 2018 and June 30, 2019 , the Company’s contract balances were as follows: December 31, 2018 June 30, 2019 Receivables, net $ 68,865 $ 60,567 Contract Assets - Current $ 656 $ 893 Contract Assets - Noncurrent 3,825 3,654 Contract Assets - Total $ 4,481 $ 4,547 Contract Liabilities - Current $ 5,513 $ 4,896 Contract Liabilities - Noncurrent 9,844 7,044 Contract Liabilities - Total $ 15,357 $ 11,940

Cash, Cash Equivalents, and R_2

Cash, Cash Equivalents, and Restricted Cash (Tables)	6 Months Ended
	Jun. 30, 2019
Cash and Cash Equivalents [Abstract]
Schedule of cash and cash equivalents	Cash, cash equivalents and restricted cash as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Current assets: Cash and cash equivalents $ 29,844 $ 40,886 Restricted cash - standby letter of credit 30 30 Restricted cash - held in escrow 750 750 Total cash, cash equivalents and current portion of restricted cash $ 30,624 $ 41,666 Long-term assets: Restricted cash - standby letter of credit $ 4,000 $ 4,000 Restricted cash - held in escrow — 848 Total long-term portion of restricted cash $ 4,000 $ 4,848 Total cash, cash equivalents and restricted cash $ 34,624 $ 46,514
Schedule of restricted cash	Cash, cash equivalents and restricted cash as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Current assets: Cash and cash equivalents $ 29,844 $ 40,886 Restricted cash - standby letter of credit 30 30 Restricted cash - held in escrow 750 750 Total cash, cash equivalents and current portion of restricted cash $ 30,624 $ 41,666 Long-term assets: Restricted cash - standby letter of credit $ 4,000 $ 4,000 Restricted cash - held in escrow — 848 Total long-term portion of restricted cash $ 4,000 $ 4,848 Total cash, cash equivalents and restricted cash $ 34,624 $ 46,514

Short-term Investments (Tables)

Short-term Investments (Tables)	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Summary of short-term investments	Short-term investments as of December 31, 2018 consisted of the following: Amortized Cost Gross Unrealized Losses Estimated Fair Value Municipal bonds and notes $ 9,210 $ (19 ) $ 9,191 Zero coupon bonds 29,823 (28 ) 29,795 Corporate bonds 26,175 (22 ) 26,153 Certificates of deposit 507 — 507 Total short-term investments $ 65,715 $ (69 ) $ 65,646 Short-term investments as of June 30, 2019 consisted of the following: Amortized Cost Gross Unrealized Gains (Losses) Estimated Fair Value Municipal bonds and notes $ 15,265 $ 2 $ 15,267 Zero coupon bonds 35,514 (2 ) 35,512 Corporate bonds 15,288 — 15,288 Certificates of deposit 517 — 517 Total short-term investments $ 66,584 $ — $ 66,584

Derivative Instruments and He_2

Derivative Instruments and Hedging Activities (Tables)	6 Months Ended
	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of derivative activity	Derivatives as of December 31, 2018 consisted of the following: Gross Amounts Recognized Gross Amounts Offset Net Amount Presented Assets: Commodity swaps: Current portion of derivative assets, related party $ 1,508 $ — $ 1,508 Long-term portion of derivative assets, related party 8,824 — 8,824 Total derivative assets $ 10,332 $ — $ 10,332 Derivatives and embedded derivatives as of June 30, 2019 consisted of the following: Gross Amounts Recognized Gross Amounts Offset Net Amount Presented Assets: Commodity swaps: Current portion of derivative assets, related party $ 655 $ — $ 655 Long-term portion of derivative assets, related party 5,041 — 5,041 Fueling agreements: Prepaid expenses and other current assets 134 — 134 Notes receivable and other long-term assets, net 316 — 316 Total derivative assets $ 6,146 $ — $ 6,146
Schedule of weighted-average price of open commodity swap contract	The following table reflects the weighted -average price of open commodity swap contracts as of December 31, 2018 and June 30, 2019 , by year with associated volumes, respectively: December 31, 2018 June 30, 2019 Year Volumes (Diesel Gallons) Weighted -Average Price per Diesel Gallon Volumes (Diesel Gallons) Weighted -Average Price per Diesel Gallon 2019 3,125,000 $ 3.18 2,500,000 $ 2.92 2020 5,000,000 $ 3.18 5,000,000 $ 2.82 2021 5,000,000 $ 3.18 5,000,000 $ 2.82 2022 5,000,000 $ 3.18 5,000,000 $ 2.82 2023 5,000,000 $ 3.18 5,000,000 $ 2.82 2024 1,875,000 $ 3.18 1,875,000 $ 2.62

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of fair value of outstanding derivative contracts	The Company estimated the fair value of its outstanding commodity swap contracts based on the following inputs as of December 31, 2018 and June 30, 2019 , respectively: December 31, 2018 June 30, 2019 Significant Unobservable Inputs Input Range Weighted Average Input Range Weighted Average ULSD Gulf Coast Forward Curve $1.71 - $1.79 $1.75 $1.80 - $1.86 $1.83 Historical Differential to PADD 3 Diesel $0.76 - $1.16 $0.89 $0.76 - $1.16 $0.90 Historical Differential to PADD 5 Diesel $1.22 - $2.12 $1.55 $1.25 - $2.30 $1.65 The Company estimated the fair value of embedded derivatives in its fueling agreements under the Zero Now truck financing program based on the following inputs as of June 30, 2019 : June 30, 2019 Significant Unobservable Inputs Input Range Weighted Average ULSD Gulf Coast Forward Curve $1.80 - $1.86 $1.83 Historical Differential to PADD 5 Diesel $1.25 - $2.30 $1.65 Historical Differential to PADD 1B Diesel $1.00 - $1.60 $1.26
Schedule of information by level for assets that are measured at fair value on a recurring basis	The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2018 and June 30, 2019 , respectively: December 31, 2018 Level 1 Level 2 Level 3 Assets: Available-for-sale securities (1) : Municipal bonds and notes $ 9,191 $ — $ 9,191 $ — Zero coupon bonds 29,795 — 29,795 — Corporate bonds 26,153 — 26,153 — Certificates of deposit (1) 507 — 507 — Commodity swap contracts (2) 10,332 — — 10,332 Embedded derivatives (3) — — — — Liabilities: Warrants (4) $ 1,079 $ — $ — $ 1,079 June 30, 2019 Level 1 Level 2 Level 3 Assets: Available-for-sale debt securities (1) : Municipal bonds and notes $ 15,267 $ — $ 15,267 $ — Zero coupon bonds 35,512 — 35,512 — Corporate bonds 15,288 — 15,288 — Certificates of deposit (1) 517 — 517 — Commodity swap contracts (2) 5,696 — — 5,696 Embedded derivatives (3) 450 — — 450 Liabilities: Warrants (4) $ 2,676 $ — $ — $ 2,676 (1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information. (2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (3) Included in “Prepaid expenses and other current assets” and “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (4) Included in “Other long-term liabilities” in the accompanying condensed consolidated balance sheets.
Schedule of information by level for liabilities that are measured at fair value on a recurring basis	The following tables provide information by level for assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2018 and June 30, 2019 , respectively: December 31, 2018 Level 1 Level 2 Level 3 Assets: Available-for-sale securities (1) : Municipal bonds and notes $ 9,191 $ — $ 9,191 $ — Zero coupon bonds 29,795 — 29,795 — Corporate bonds 26,153 — 26,153 — Certificates of deposit (1) 507 — 507 — Commodity swap contracts (2) 10,332 — — 10,332 Embedded derivatives (3) — — — — Liabilities: Warrants (4) $ 1,079 $ — $ — $ 1,079 June 30, 2019 Level 1 Level 2 Level 3 Assets: Available-for-sale debt securities (1) : Municipal bonds and notes $ 15,267 $ — $ 15,267 $ — Zero coupon bonds 35,512 — 35,512 — Corporate bonds 15,288 — 15,288 — Certificates of deposit (1) 517 — 517 — Commodity swap contracts (2) 5,696 — — 5,696 Embedded derivatives (3) 450 — — 450 Liabilities: Warrants (4) $ 2,676 $ — $ — $ 2,676 (1) Included in “Short-term investments” in the accompanying condensed consolidated balance sheets. See Note 5 for more information. (2) Included in “Derivative assets, related party” and “Long-term portion of derivative assets, related party” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (3) Included in “Prepaid expenses and other current assets” and “Notes receivable and other long-term assets, net” in the accompanying condensed consolidated balance sheets. See Note 6 for more information. (4) Included in “Other long-term liabilities” in the accompanying condensed consolidated balance sheets.
Schedule of reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis that used significant unobservable inputs (Level 3)	The following table provides a reconciliation of the beginning and ending balances of items measured at fair value on a recurring basis as shown in the tables above that used significant unobservable inputs (Level 3): Assets: Commodity Swap Contracts Assets: Embedded Derivatives Liabilities: Warrants Balance as of December 31, 2017 $ — $ — $ (536 ) Gain (loss) included in earnings — — 92 Balance as of June 30, 2018 $ — $ — $ (444 ) Balance as of December 31, 2018 $ 10,332 $ — $ (1,079 ) Settlements, net 209 — — Gain (loss) included in earnings (4,845 ) 450 (1,597 ) Balance as of June 30, 2019 $ 5,696 $ 450 $ (2,676 )

Other Receivables (Tables)

Other Receivables (Tables)	6 Months Ended
	Jun. 30, 2019
Receivables [Abstract]
Schedule of other receivables	Other receivables as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Loans to customers to finance vehicle purchases $ 276 $ 1,821 Accrued customer billings 6,261 5,897 Fuel tax credits 434 434 Other 8,573 1,256 Total other receivables $ 15,544 $ 9,408

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2019
Inventory Disclosure [Abstract]
Schedule of inventories	Inventory as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Raw materials and spare parts $ 34,890 $ 33,781 Finished goods 85 89 Total inventory $ 34,975 $ 33,870

Land, Property and Equipment (T

Land, Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2019
Property, Plant and Equipment [Abstract]
Summary of land, property and equipment	Land, property and equipment as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Land $ 3,681 $ 3,681 LNG liquefaction plants 94,633 94,633 Station equipment 319,119 315,547 Trailers 75,901 75,242 Other equipment 97,268 98,424 Construction in progress 73,485 75,995 664,087 663,522 Less: accumulated depreciation (313,519 ) (334,892 ) Total land, property and equipment, net $ 350,568 $ 328,630

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	6 Months Ended
	Jun. 30, 2019
Payables and Accruals [Abstract]
Schedule of accrued liabilities	Accrued liabilities as of December 31, 2018 and June 30, 2019 consisted of the following: December 31, June 30, Accrued alternative fuels incentives $ 6,923 $ 6,212 Accrued employee benefits 2,248 3,009 Accrued interest 78 1,142 Accrued gas and equipment purchases 12,833 7,774 Accrued property and other taxes 3,397 4,605 Accrued salaries and wages 8,609 5,681 Other 14,381 11,340 Total accrued liabilities $ 48,469 $ 39,763

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Schedule of debt obligations	Debt obligations as of December 31, 2018 and June 30, 2019 consisted of the following and are further discussed below: December 31, 2018 Principal Balances Unamortized Debt Financing Costs Balance, Net of Financing Costs 7.5% Notes $ 50,000 $ 58 $ 49,942 NG Advantage debt 28,904 155 28,749 Other debt 1,024 — 1,024 Total debt 79,928 213 79,715 Less amounts due within one year (4,811 ) (99 ) (4,712 ) Total long-term debt $ 75,117 $ 114 $ 75,003 June 30, 2019 Principal Balances Unamortized Debt Financing Costs Balance Net of Financing Costs 7.5% Notes $ 50,000 $ 38 $ 49,962 NG Advantage debt 29,726 126 29,600 Other debt 912 — 912 Total debt 80,638 164 80,474 Less amounts due within one year (55,620 ) (58 ) (55,562 ) Total long-term debt $ 25,018 $ 106 $ 24,912

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Schedule of information required to compute basic and diluted net loss per share	The information required to compute basic and diluted net income (loss) per share is as follows: Three Months Ended Six Months Ended 2018 2019 2018 2019 Weighted-average common shares outstanding 162,613,316 204,653,723 157,432,786 204,426,459 Dilutive effect of potential common shares from restricted stock units and stock options — — 4,249,459 — Weighted-average common shares outstanding -diluted 162,613,316 204,653,723 161,682,245 204,426,459
Schedule of potentially dilutive securities that have been excluded from the diluted net loss per share calculations because their effect would have been antidilutive	The following potentially dilutive securities have been excluded from the diluted net income (loss) per share calculations because their effect would have been antidilutive. Although these securities were antidilutive for these periods, they could be dilutive in future periods. Three Months Ended Six Months Ended 2018 2019 2018 2019 Stock options 10,127,427 10,192,762 8,329,642 10,192,762 Convertible notes 13,409,242 3,164,557 13,409,242 3,164,557 Restricted stock units 2,451,674 1,289,751 2,451,674 1,289,751 Total 25,988,343 14,647,070 24,190,558 14,647,070

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of compensation expense and related income tax benefit related to the stock-based compensation expense recognized	The following table summarizes the compensation expense and related income tax benefit related to the Company’s stock-based compensation arrangements recognized in the accompanying condensed consolidated statements of operations during the periods: Three Months Ended Six Months Ended 2018 2019 2018 2019 Stock-based compensation expense, net of $0 tax in 2018 and 2019 $ 1,208 $ 918 $ 3,106 $ 2,164

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Schedule of finance and operating lease asset and liability balances	As of June 30, 2019 , the Company’s finance and operating lease asset and liability balances were as follows: June 30, 2019 Finance leases: Land, property and equipment, gross $ 5,917 Accumulated depreciation (1,927 ) Land, property and equipment, net $ 3,990 Current portion of finance lease obligations $ 654 Long-term portion of finance lease obligations 3,236 Total finance lease liabilities $ 3,890 Operating leases: Operating lease right-of-use assets (1) $ 24,490 Current portion of operating lease obligations $ 3,570 Long-term portion of operating lease obligations 22,245 Total operating lease liabilities $ 25,815 (1) The Company’s operating lease ROU assets are comprised of the following: June 30, 2019 Assets Liabilities Real estate for fueling stations $ 18,432 $ 18,432 LNG plant, office spaces and warehouses 6,048 7,373 Office equipment 10 10 Total operating lease right-of-use assets $ 24,490 $ 25,815
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: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Finance leases: Depreciation on assets under finance leases $ 105 $ 364 Interest on lease liabilities 50 99 Total finance leases expense $ 155 $ 463 Operating leases: Lease expense $ 1,618 $ 3,101 Lease expense on short-term leases 485 1,587 Variable lease expense 699 1,330 Sublease income (52 ) (103 ) Total operating leases expense $ 2,750 $ 5,915 Supplemental information on finance and operating leases are as follows: Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating cash outflows from finance leases $ (49 ) $ (98 ) Operating cash outflows from operating leases $ (710 ) $ (1,860 ) Financing cash outflows from finance leases $ (665 ) $ (849 ) Assets obtained in exchange for new finance lease liabilities (1) $ 134 $ 263 ROU assets obtained in exchange for new operating lease liabilities (1) $ 1,732 $ 1,732 June 30, 2019 Weighted-average remaining lease term - finance leases 4.91 years Weighted-average remaining lease term - operating leases 11.24 years Weighted-average discount rate - finance leases 4.72% Weighted-average discount rate - operating leases 8.20% (1) These amounts are excluded from the accompanying condensed consolidated statements of cash flows as they are non-cash investing activities.
Schedule of maturities of operating lease liabilities	The following schedule represents the Company’s maturities of finance and operating lease liabilities as of June 30, 2019 : Finance Leases Operating Leases Fiscal year: 2019 $ 437 $ 2,808 2020 752 4,627 2021 662 3,720 2022 555 2,809 2023 479 2,807 Thereafter 1,610 24,242 Total minimum lease payments 4,495 41,013 Less amount representing interest (605 ) (15,198 ) Present value of lease liabilities $ 3,890 $ 25,815
Schedule of maturities of finance lease liabilities	The following schedule represents the Company’s maturities of finance and operating lease liabilities as of June 30, 2019 : Finance Leases Operating Leases Fiscal year: 2019 $ 437 $ 2,808 2020 752 4,627 2021 662 3,720 2022 555 2,809 2023 479 2,807 Thereafter 1,610 24,242 Total minimum lease payments 4,495 41,013 Less amount representing interest (605 ) (15,198 ) Present value of lease liabilities $ 3,890 $ 25,815
Schedule of maturities of lease receivables	The following schedule represents the Company’s maturities of lease receivables as of June 30, 2019 : Fiscal year: 2019 $ 93 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Total minimum lease payments 2,077 Less amount representing interest (1,007 ) Present value of lease receivables $ 1,070
Schedule of future minimum lease obligations under noncancelable operating leases	The following schedule represents the Company’s future minimum lease obligations under all noncancelable operating leases as of December 31, 2018 : Fiscal year: 2019 $ 6,340 2020 4,332 2021 3,311 2022 2,409 2023 2,300 Thereafter 13,214 Total future minimum lease payments $ 31,906
Schedule of future payments under capital leases	The Company leases equipment under capital leases with a weighted-average interest rate of 4.48% . As of December 31, 2018 , future payments under these capital leases are as follows: Fiscal year: 2019 $ 883 2020 742 2021 656 2022 540 2023 529 Thereafter 1,868 Total minimum lease payments 5,218 Less amount representing interest (749 ) Capital lease obligations 4,469 Less current portion (693 ) Capital lease obligations, less current portion $ 3,776
Schedule of future receipts under capital leases	As of December 31, 2018 , future receipts under this lease are as follows: Fiscal year: 2019 $ 186 2020 186 2021 186 2022 186 2023 186 Thereafter 1,240 Capital lease receivables 2,170 Less amount representing interest (1,080 ) Capital lease receivables, less current portion $ 1,090

Recently Adopted Accounting C_2

Recently Adopted Accounting Changes (Tables)	6 Months Ended
	Jun. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Schedule of adoption adjustments	The ASC 842 adoption adjustments are as follows: Balance as of December 31, 2018 Adjustments Due to ASC 842 Balance as of January 1, 2019 Operating lease right-of-use assets $ — $ 24,453 $ 24,453 Operating lease obligations $ — $ 25,943 $ 25,943 Accrued liabilities $ 48,469 $ (496 ) $ 47,973 Other long-term liabilities $ 15,035 $ (994 ) $ 14,041 The ASC 842 adoption adjustments on the accompanying condensed consolidated balance sheet as of June 30, 2019 are as follows: June 30, 2019 Balance before ASC 842 Adoption Effect of Change As Reported Operating lease right-of-use assets $ — $ 24,490 $ 24,490 Current portion of operating lease obligations $ — $ 3,570 $ 3,570 Long-term portion of operating lease obligations $ — $ 22,245 $ 22,245 Accrued liabilities $ 40,294 $ (531 ) $ 39,763 Other long-term liabilities $ 13,611 $ (710 ) $ 12,901

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 72,318	$ 70,467	$ 150,016	$ 172,870
Gain (loss) on change in fair value of commodity swaps	(17)	(70)	1,597	(92)
Receivables, net	60,567		60,567		$ 68,865
Contract Assets - Current	893		893		656
Contract Assets - Noncurrent	3,654		3,654		3,825
Contract Assets - Total	4,547		4,547		4,481
Contract Liabilities - Current	4,896		4,896		5,513
Contract Liabilities - Noncurrent	7,044		7,044		9,844
Contract Liabilities - Total	11,940		11,940		$ 15,357
Volume -related
Disaggregation of Revenue [Line Items]
Revenue	66,260	62,642	140,788	129,978
Gain (loss) on change in fair value of commodity swaps	565		(4,395)
Station construction sales
Disaggregation of Revenue [Line Items]
Revenue	5,943	5,781	9,113	11,579
Alternative fuels excise tax credit (“AFTC”)
Disaggregation of Revenue [Line Items]
Revenue	0	1,382	0	26,863
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 115	$ 662	$ 115	$ 4,450

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue, remaining performance obligation	$ 10,825
Contract with customer, liability, revenue recognized	$ 4,412	$ 1,479

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01	Jun. 30, 2019
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years

Investments in Other Entities_2

Investments in Other Entities and Noncontrolling Interest in a Subsidiary (Details) - USD ($)	Jun. 28, 2019	Jun. 11, 2019	Apr. 15, 2019	Feb. 15, 2019	Oct. 01, 2018	Feb. 28, 2018	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Feb. 28, 2019	Jun. 30, 2019	Jun. 30, 2018	May 17, 2019	Dec. 29, 2017	Oct. 14, 2014
Acquisition and Divestitures
Loss from equity method investments											$ 33,000	$ 729,000		$ 500,000	$ 2,197,000
Investment balance									$ 26,079,000		26,072,000			26,072,000
Outstanding balance									$ 79,715,000		80,474,000			80,474,000
Loss from noncontrolling interest											$ 1,711,000	1,186,000		$ 3,590,000	2,935,000
Common unit purchase agreement | NG Advantage
Acquisition and Divestitures
Issuance of equity by subsidiary to parent (in shares)							100,000,000	100,000,000	100,000,000	100,000			400,000
Common unit purchase agreement | NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent					61.70%	53.50%
Common unit purchase agreement | NG Advantage | NG Advantage
Acquisition and Divestitures
Noncontrolling interest, ownership percentage by parent											64.60%			64.60%
BP Products North America | Long-Term Natural Gas Purchase Contracts | NG Advantage
Acquisition and Divestitures
Contingent consideration, liability (up to)						$ 30,000,000
Contingent consideration, liability, term						30 days
Clean Energy Fuels Corp. | NG Advantage
Acquisition and Divestitures
Number of common units to be called by warrant (in shares)	86,879
Clean Energy Fuels Corp. | NG Advantage | Convertible Debt
Acquisition and Divestitures
Debt issuance amount	$ 15,188,000			$ 5,000,000												$ 500,000
Proceeds from convertible debt	$ 3,500,000	$ 144,000	$ 2,500,000	$ 2,500,000
Outstanding balance											$ 8,688,000			$ 8,688,000
SAFE&CEC S.r.l.
Acquisition and Divestitures
Ownership interest																	49.00%
Loss from equity method investments											6,000	706,000		446,000	2,147,000
Investment balance									$ 23,372,000		23,419,000			23,419,000
SAFE&CEC S.r.l. | Landi Renzo S.p.A.
Acquisition and Divestitures
Ownership interest																	51.00%
NG Advantage
Acquisition and Divestitures
Loss from noncontrolling interest											1,711,000	$ 1,186,000		3,590,000	$ 2,935,000
Noncontrolling interest, fair value									$ 17,011,000		$ 13,193,000			$ 13,193,000
NG Advantage | Common unit purchase agreement
Acquisition and Divestitures
Ownership interest acquired																		53.30%
Stock issued during period, acquisitions (in shares)					1,000,001	19,660
Payments to acquire additional controlling interest					$ 5,000,000

Cash, Cash Equivalents, and R_3

Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Cash and cash equivalents	$ 40,886	$ 29,844
Total cash, cash equivalents and current portion of restricted cash	41,666	30,624
Long-term portion of restricted cash	4,848	4,000
Total cash, cash equivalents and restricted cash	46,514	34,624	$ 43,407	$ 37,208
Cash in excess of insurance limits	39,556	28,524
Held in escrow
Line of Credit Facility [Line Items]
Restricted cash	750	750
Long-term portion of restricted cash	848	0
Standby letters of credit
Line of Credit Facility [Line Items]
Restricted cash	30	30
Long-term portion of restricted cash	$ 4,000	$ 4,000

Short-term Investments (Details

Short-term Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Short-term investments
Amortized Cost	$ 66,584	$ 65,715
Gross Unrealized Gains (Losses)	0	(69)
Estimated Fair Value	66,584	65,646
Municipal bonds and notes
Short-term investments
Amortized Cost	15,265	9,210
Gross Unrealized Gains (Losses)	2	(19)
Estimated Fair Value	15,267	9,191
Zero coupon bonds
Short-term investments
Amortized Cost	35,514	29,823
Gross Unrealized Gains (Losses)	(2)	(28)
Estimated Fair Value	35,512	29,795
Corporate bonds
Short-term investments
Amortized Cost	15,288	26,175
Gross Unrealized Gains (Losses)	0	(22)
Estimated Fair Value	15,288	26,153
Certificates of deposit
Short-term investments
Amortized Cost	517	507
Gross Unrealized Gains (Losses)	0	0
Estimated Fair Value	$ 517	$ 507

Derivative Instruments and He_3

Derivative Instruments and Hedging Activities - Narrative (Details) - Not Designated as Hedging Instrument - Commodity swap contracts	Jun. 30, 2019$ / galgal	Dec. 31, 2018$ / galgal	Oct. 31, 2018contractgal
Derivative [Line Items]
Derivative asset, number of instruments held | contract			2
Volumes (diesel gallons) | gal	24,400,000	25,000,000	5,000,000
Weighted -average price per diesel gallon (in usd per gallon) | $ / gal	2.82	3.18

Derivative Instruments and He_4

Derivative Instruments and Hedging Activities - Summary of Derivative Activity (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Gross Amounts Recognized	$ 6,146	$ 10,332
Gross Amounts Offset	0	0
Net Amount Presented	6,146	10,332
Current portion of derivative assets, related party | Commodity swap contracts
Derivative [Line Items]
Gross Amounts Recognized	655	1,508
Gross Amounts Offset	0	0
Net Amount Presented	655	1,508
Long-term portion of derivative assets, related party | Commodity swap contracts
Derivative [Line Items]
Gross Amounts Recognized	5,041	8,824
Gross Amounts Offset	0	0
Net Amount Presented	5,041	$ 8,824
Prepaid expenses and other current assets | Fueling agreements
Derivative [Line Items]
Gross Amounts Recognized	134
Gross Amounts Offset	0
Net Amount Presented	134
Notes receivable and other long-term assets, net | Fueling agreements
Derivative [Line Items]
Gross Amounts Recognized	316
Gross Amounts Offset	0
Net Amount Presented	$ 316

Derivative Instruments and He_5

Derivative Instruments and Hedging Activities - Schedule of Weighted-Average Price of Open Commodity Wwap Contracts (Details) - Not Designated as Hedging Instrument gal in Thousands	Jun. 30, 2019$ / galgal	Dec. 31, 2018$ / galgal
Commodity Swap 2019
Derivative [Line Items]
Volumes (diesel gallons) | gal	2,500	3,125
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.92	3.18
Commodity Swap 2020
Derivative [Line Items]
Volumes (diesel gallons) | gal	5,000	5,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.82	3.18
Commodity Swap 2021
Derivative [Line Items]
Volumes (diesel gallons) | gal	5,000	5,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.82	3.18
Commodity Swap 2022
Derivative [Line Items]
Volumes (diesel gallons) | gal	5,000	5,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.82	3.18
Commodity Swap 2023
Derivative [Line Items]
Volumes (diesel gallons) | gal	5,000	5,000
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.82	3.18
Commodity Swap 2024
Derivative [Line Items]
Volumes (diesel gallons) | gal	1,875	1,875
Weighted -Average Price per Diesel Gallon (in usd per gallon) | $ / gal	2.62	3.18

Fair Value Measurements - Deriv

Fair Value Measurements - Derivative Contracts (Details) - Not Designated as Hedging Instrument - Valuation Technique, Discounted Cash Flow - Level 3	Jun. 30, 2019	Dec. 31, 2018
Commodity swap contracts | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.80	1.71
Commodity swap contracts | Minimum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.76	0.76
Commodity swap contracts | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.25	1.22
Commodity swap contracts | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.86	1.79
Commodity swap contracts | Maximum | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.16	1.16
Commodity swap contracts | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.30	2.12
Commodity swap contracts | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.83	1.75
Commodity swap contracts | Weighted Average | Historical Differential to PADD 3 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.90	0.89
Commodity swap contracts | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.65	1.55
Fueling agreements | Minimum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.80
Fueling agreements | Minimum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.25
Fueling agreements | Minimum | Historical Differential to PADD 1B Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1
Fueling agreements | Maximum | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.86
Fueling agreements | Maximum | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	2.30
Fueling agreements | Maximum | Historical Differential to PADD 1B Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.60
Fueling agreements | Weighted Average | ULSD Gulf Coast Forward Curve
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.83
Fueling agreements | Weighted Average | Historical Differential to PADD 5 Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.65
Fueling agreements | Weighted Average | Historical Differential to PADD 1B Diesel
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.26

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Available-for-sale securities	$ 66,584	$ 65,646
Short-term investments	66,584	65,646
Fair value measured on recurring basis | Municipal bonds and notes
Assets:
Available-for-sale securities	15,267	9,191
Fair value measured on recurring basis | Zero coupon bonds
Assets:
Available-for-sale securities	35,512	29,795
Fair value measured on recurring basis | Corporate bonds
Assets:
Available-for-sale securities	15,288	26,153
Fair value measured on recurring basis | Certificates of deposit
Assets:
Short-term investments	517	507
Fair value measured on recurring basis | Commodity swap contracts
Assets:
Derivative	5,696	10,332
Fair value measured on recurring basis | Embedded derivatives
Assets:
Derivative	450	0
Fair value measured on recurring basis | Warrants
Liabilities:
Warrants	2,676	1,079
Fair value measured on recurring basis | Level 1 | Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 1 | Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 1 | Corporate bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 1 | Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis | Level 1 | Commodity swap contracts
Assets:
Derivative	0	0
Fair value measured on recurring basis | Level 1 | Embedded derivatives
Assets:
Derivative	0	0
Fair value measured on recurring basis | Level 1 | Warrants
Liabilities:
Warrants	0	0
Fair value measured on recurring basis | Level 2 | Municipal bonds and notes
Assets:
Available-for-sale securities	15,267	9,191
Fair value measured on recurring basis | Level 2 | Zero coupon bonds
Assets:
Available-for-sale securities	35,512	29,795
Fair value measured on recurring basis | Level 2 | Corporate bonds
Assets:
Available-for-sale securities	15,288	26,153
Fair value measured on recurring basis | Level 2 | Certificates of deposit
Assets:
Short-term investments	517	507
Fair value measured on recurring basis | Level 2 | Commodity swap contracts
Assets:
Derivative	0	0
Fair value measured on recurring basis | Level 2 | Embedded derivatives
Assets:
Derivative	0	0
Fair value measured on recurring basis | Level 2 | Warrants
Liabilities:
Warrants	0	0
Fair value measured on recurring basis | Level 3 | Municipal bonds and notes
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 3 | Zero coupon bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 3 | Corporate bonds
Assets:
Available-for-sale securities	0	0
Fair value measured on recurring basis | Level 3 | Certificates of deposit
Assets:
Short-term investments	0	0
Fair value measured on recurring basis | Level 3 | Commodity swap contracts
Assets:
Derivative	5,696	10,332
Fair value measured on recurring basis | Level 3 | Embedded derivatives
Assets:
Derivative	450	0
Fair value measured on recurring basis | Level 3 | Warrants
Liabilities:
Warrants	$ 2,676	$ 1,079

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Recognition - Assets (Details) - Derivative Financial Instruments, Assets - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Commodity swap contracts
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	$ 10,332	$ 0
Settlements, net	209
Gain (loss) included in earnings	(4,845)	0
Ending balance	5,696	0
Embedded derivatives
Reconciliation of the beginning and ending balances of assets measured at fair value using significant unobservable inputs (Level 3)
Beginning balance	0	0
Settlements, net	0
Gain (loss) included in earnings	450	0
Ending balance	$ 450	$ 0

Fair Value Measurements - Fai_2

Fair Value Measurements - Fair Value Recognition - Liabilities (Details) - Warrants - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Reconciliation of the beginning and ending balances of liabilities measured at fair value using significant unobservable inputs (Level 3)
Beginning Balance	$ (1,079)	$ (536)
Settlements, net	0
Gain (loss) included in earnings	(1,597)	92
Ending Balance	$ (2,676)	$ (444)

Other Receivables (Details)

Other Receivables (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Other Receivables
Other receivables	$ 9,408	$ 15,544
Loans to customers to finance vehicle purchases
Other Receivables
Other receivables	1,821	276
Accrued customer billings
Other Receivables
Other receivables	5,897	6,261
Fuel tax credits
Other Receivables
Other receivables	434	434
Other
Other Receivables
Other receivables	$ 1,256	$ 8,573

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials and spare parts	$ 33,781	$ 34,890
Finished goods	89	85
Total inventory	$ 33,870	$ 34,975

Land, Property and Equipment (D

Land, Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Land, Property and Equipment
Land, property and equipment, gross	$ 663,522		$ 663,522		$ 664,087
Less: accumulated depreciation	(334,892)		(334,892)		(313,519)
Total land, property and equipment, net	328,630		328,630		350,568
Capitalized software costs	29,987		29,987		29,344
Accumulated amortization on the capitalized software costs	24,568		24,568		22,472
Amortization expense related to the capitalized software costs	1,064	$ 955	2,099	$ 1,673
Property and equipment purchases included in accounts payable and accrued liabilities	817		817		1,536
Land
Land, Property and Equipment
Land, property and equipment, gross	3,681		3,681		3,681
LNG liquefaction plants
Land, Property and Equipment
Land, property and equipment, gross	94,633		94,633		94,633
Station equipment
Land, Property and Equipment
Land, property and equipment, gross	315,547		315,547		319,119
Trailers
Land, Property and Equipment
Land, property and equipment, gross	75,242		75,242		75,901
Other equipment
Land, Property and Equipment
Land, property and equipment, gross	98,424		98,424		97,268
Construction in progress
Land, Property and Equipment
Land, property and equipment, gross	$ 75,995		$ 75,995		$ 73,485

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued alternative fuels incentives	$ 6,212		$ 6,923
Accrued employee benefits	3,009		2,248
Accrued interest	1,142		78
Accrued gas and equipment purchases	7,774		12,833
Accrued property and other taxes	4,605		3,397
Accrued salaries and wages	5,681		8,609
Other	11,340		14,381
Total accrued liabilities	$ 39,763	$ 47,973	$ 48,469

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2013
Principal Balances
Total debt	$ 80,638	$ 79,928
Less amounts due within one year	(55,620)	(4,811)
Total long-term debt	25,018	75,117
Unamortized Debt Financing Costs
Total debt	164	213
Less amounts due within one year	(58)	(99)
Total long-term debt	106	114
Balance, Net of Financing Costs
Total debt	80,474	79,715
Less amounts due within one year	(55,562)	(4,712)
Total long-term debt	24,912	75,003
7.5% Notes
Principal Balances
Total debt	50,000	50,000
Unamortized Debt Financing Costs
Total debt	38	58
Balance, Net of Financing Costs
Total debt	$ 49,962	49,942
Interest rate	7.50%		7.50%
NG Advantage debt
Principal Balances
Total debt	$ 29,726	28,904
Unamortized Debt Financing Costs
Total debt	126	155
Balance, Net of Financing Costs
Total debt	29,600	28,749
Other debt
Principal Balances
Total debt	912	1,024
Unamortized Debt Financing Costs
Total debt	0	0
Balance, Net of Financing Costs
Total debt	$ 912	$ 1,024

Debt - 7.5% Notes (Details)

Debt - 7.5% Notes (Details)	Dec. 04, 2018USD ($)	Jun. 29, 2018USD ($)	Jun. 30, 2013USD ($)day$ / sharesshares	Dec. 31, 2017USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Long-term debt [Line Items]
Aggregate principal amount					$ 80,638,000	$ 79,928,000
7.5% Notes
Long-term debt [Line Items]
Interest rate			7.50%		7.50%
Debt issuance amount			$ 150,000,000
Debt instrument, repurchase amount during period	$ 50,000,000
Payments for repurchase and retirement of debt instrument	$ 50,500,000
Aggregate principal amount					$ 50,000,000	$ 50,000,000
7.5% Notes | Buyers
Long-term debt [Line Items]
Conversion price of shares (in dollars per share) | $ / shares			$ 15.80
Percentage of the trade price of common stock that the conversion price must be at premium for the Company to force conversion			40.00%
Number of days within 30 consecutive trading days in which the trade price of the entity's common stock must be at premium of the conversion price for the Company to force conversion (at least) | day			20
Number of consecutive trading days used to determine the conversion obligation on the notes for the Company to force conversion | day			30
Period during which the debt instrument principal balance is required to be paid following its issuance			7 years
Repayment in shares at maturity covenant, maximum number of shares (in shares) | shares			13,993,630
7.5% Notes | Green Energy Investment Holdings, LLC
Long-term debt [Line Items]
Debt instrument, repurchase amount during period		$ 25,000,000
Principal amount transferred				$ 16,800,000
Payment of accrued and unpaid interest		$ 505,000
Aggregate principal amount					32,906,000
7.5% Notes | Green Energy Investment Holdings, LLC | Boone Pickens
Long-term debt [Line Items]
Debt instrument, repurchase amount during period				$ 25,000,000
7.5% Notes | Other Third Parties
Long-term debt [Line Items]
Aggregate principal amount					$ 17,094,000

Debt - Plains Credit Facility (

Debt - Plains Credit Facility (Details) - Plains Credit Facility - USD ($)	Feb. 29, 2016	Jun. 30, 2019
Long-term debt [Line Items]
Line of credit limit	$ 50,000,000
Line of credit		$ 0
Interest rate	2.70%
LIBOR
Long-term debt [Line Items]
Basis spread on variable rate	2.30%

Debt - Soci_t_ G_n_rale Term Lo

Debt - Société Générale Term Loan Facility (Details) - Line of Credit - Société Générale - Term Loan Facility	Jan. 02, 2019USD ($)
Line of Credit Facility [Line Items]
Line of credit limit	$ 100,000,000
Unused capacity, commitment fee percentage	0.39%
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.30%

Debt - TOTAL Credit Support Agr

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

Debt - NG Advantage Debt (Detai

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

Debt - Other Debt (Details)

Debt - Other Debt (Details) - Other Debt	Jun. 30, 2019	Dec. 31, 2018
Long-term debt [Line Items]
Weighted average interest rate	4.78%	4.78%
Maximum
Long-term debt [Line Items]
Interest rate	5.02%

Net Income (Loss) Per Share - B

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Weighted-average common shares outstanding (in shares)	204,653,723	162,613,316	204,426,459	157,432,786
Dilutive effect of potential common shares from restricted stock units and stock options (in shares)	0	0	0	4,249,459
Weighted-average common shares outstanding - diluted (in shares)	204,653,723	162,613,316	204,426,459	161,682,245

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Anti-dilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Loss Per Share
Anti-dilutive securities (in shares)	14,647,070	25,988,343	14,647,070	24,190,558
Stock Options
Net Loss Per Share
Anti-dilutive securities (in shares)	10,192,762	10,127,427	10,192,762	8,329,642
Convertible Notes
Net Loss Per Share
Anti-dilutive securities (in shares)	3,164,557	13,409,242	3,164,557	13,409,242
Restricted stock units
Net Loss Per Share
Anti-dilutive securities (in shares)	1,289,751	2,451,674	1,289,751	2,451,674

Stock-Based Compensation (Detai

Stock-Based Compensation (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation expense, net of $0 tax in 2018 and 2019	$ 918,000	$ 1,208,000	$ 2,164,000	$ 3,106,000
Stock-based compensation expense, tax	0	$ 0	0	$ 0
Unrecognized compensation cost	$ 4,643,000		$ 4,643,000
Unrecognized compensation cost, weighted-average period			1 year 8 months 25 days

Stockholders_ Equity (Details)

Stockholders’ Equity (Details) - Purchase Agreement - USD ($) $ / shares in Units, $ in Thousands	Jun. 13, 2018	May 09, 2018
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)		50,856,296
Price per share (in dollars per share)		$ 1.64
Percentage of ownership after transaction	25.00%
Consideration received on transaction	$ 83,404
Fees and issuance costs	$ 1,909
Purchase Percentage Covenant, Threshold
Subsidiary, Sale of Stock [Line Items]
Percentage of ownership after transaction		5.00%
Purchase Percentage Covenant, Maximum
Subsidiary, Sale of Stock [Line Items]
Percentage of ownership after transaction		30.00%

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income tax expense	$ 66	$ 89	$ 126	$ 177
Unrecognized tax benefits, increase from portion of AFTC revenue offset by the fuel tax				$ 2,689

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Residual value of leased asset	$ 1,381		$ 1,381
Sales-type lease, interest income	$ 37		73
Operating leases, rent expense, including variable rent		$ 1,698		$ 3,225
Capital leases weighted average interest rate					4.48%
Capital leased assets, gross					$ 6,143
Capital leases, accumulated depreciation					$ 1,832
Capital leases, sales type leases, interest rate					13.50%
T. Boone Pickens
Lessee, Lease, Description [Line Items]
Lessee, operating lease, monthly rental payments			$ 12

Leases - Finance and Operating

Leases - Finance and Operating Lease Asset and Liability Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Finance leases:
Land, property and equipment, gross	$ 5,917
Accumulated depreciation	(1,927)
Land, property and equipment, net	3,990
Current portion of finance lease obligations	654		$ 693
Long-term portion of finance lease obligations	3,236		3,776
Total finance lease liabilities	3,890
Operating leases:
Operating lease right-of-use assets	24,490	$ 24,453	0
Current portion of operating lease obligations	3,570		0
Long-term portion of operating lease obligations	22,245
Total operating lease liabilities	25,815	$ 25,943	$ 0
Real estate for fueling stations
Operating leases:
Operating lease right-of-use assets	18,432
Total operating lease liabilities	18,432
LNG plant, office spaces and warehouses
Operating leases:
Operating lease right-of-use assets	6,048
Total operating lease liabilities	7,373
Office equipment
Operating leases:
Operating lease right-of-use assets	10
Total operating lease liabilities	$ 10

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Finance leases:
Depreciation on assets under finance leases	$ 105	$ 364
Interest on lease liabilities	50	99
Total finance leases expense	155	463
Operating leases:
Lease expense	1,618	3,101
Lease expense on short-term leases	485	1,587
Variable lease expense	699	1,330
Sublease income	(52)	(103)
Total operating leases expense	$ 2,750	$ 5,915

Leases - Supplemental Informati

Leases - Supplemental Information (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Leases [Abstract]
Operating cash outflows from finance leases	$ (49)	$ (98)
Operating cash outflows from operating leases	(710)	(1,860)
Financing cash outflows from finance leases	(665)	(849)
Assets obtained in exchange for new finance lease liabilities	134	263
ROU assets obtained in exchange for new operating lease liabilities	$ 1,732	$ 1,732
Weighted-average remaining lease term - finance leases	4 years 10 months 27 days	4 years 10 months 27 days
Weighted-average remaining lease term - operating leases	11 years 2 months 27 days	11 years 2 months 27 days
Weighted-average discount rate - finance leases	4.72%	4.72%
Weighted-average discount rate - operating leases	8.20%	8.20%

Leases - Maturities of Finance

Leases - Maturities of Finance and Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Finance Leases
2019	$ 437
2020	752
2021	662
2022	555
2023	479
Thereafter	1,610
Total minimum lease payments	4,495
Less amount representing interest	(605)
Present value of lease liabilities	3,890
Operating Leases
2019	2,808
2020	4,627
2021	3,720
2022	2,809
2023	2,807
Thereafter	24,242
Total minimum lease payments	41,013
Less amount representing interest	(15,198)
Present value of lease liabilities	$ 25,815	$ 25,943	$ 0

Leases - Maturities of Lease Re

Leases - Maturities of Lease Receivables (Details) $ in Thousands	Jun. 30, 2019USD ($)
Fiscal year:
2019	$ 93
2020	186
2021	186
2022	186
2023	186
Thereafter	1,240
Total minimum lease payments	2,077
Less amount representing interest	(1,007)
Present value of lease receivables	$ 1,070

Leases - Operating Lease Commit

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

Leases - Capitalized Lease Obli

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

Leases - Capitalized Lease Rece

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

Alternative Fuels Excise Tax _2

Alternative Fuels Excise Tax Credit (Details) $ in Thousands	3 Months Ended	12 Months Ended		17 Months Ended
	Jun. 30, 2018USD ($)	Dec. 31, 2017$ / gallon	Dec. 31, 2016$ / gallon	Jun. 30, 2019USD ($)
Alternative Fuels Excise Tax Credit
Federal alternative fuels tax credit - CNG (in dollars per gasoline gallon equivalent)		0.50
Federal alternative fuels tax credit - LNG (in dollars per liquid gallon)		0.50	0.50
Federal alternative fuels tax credit - credits recognized as revenue | $	$ 1,382			$ 25,481

Recently Adopted Accounting C_3

Recently Adopted Accounting Changes (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 24,490	$ 24,453	$ 0
Operating lease obligations	25,815	25,943	0
Current portion of operating lease obligations	3,570		0
Long-term portion of operating lease obligations	22,245
Accrued liabilities	39,763	47,973	48,469
Other long-term liabilities	12,901	14,041	$ 15,035
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets		24,453
Operating lease obligations		25,943
Accrued liabilities		(496)
Other long-term liabilities		$ (994)
Balance before ASC 842 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	0
Current portion of operating lease obligations	0
Long-term portion of operating lease obligations	0
Accrued liabilities	40,294
Other long-term liabilities	13,611
Effect of Change | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	24,490
Current portion of operating lease obligations	3,570
Long-term portion of operating lease obligations	22,245
Accrued liabilities	(531)
Other long-term liabilities	$ (710)

Uncategorized Items - clne-2019

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