Plug Power (PLUG) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 08, 2021
Document and Entity Information:
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	1-34392
Entity Registrant Name	Plug Power Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-3672377
Entity Address, Address Line One	968 ALBANY SHAKER ROAD
Entity Address, City or Town	LATHAM
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	12110
City Area Code	518
Local Phone Number	782-7700
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	PLUG
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		576,355,807
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Entity Central Index Key	0001093691
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 3,371,962	$ 1,312,404
Restricted cash	90,688	64,041
Available-for-sale securities, at fair value (amortized cost $756,841 and allowance for credit losses of $0 at September 30, 2021)	752,766
Equity securities	147,649
Accounts receivable	132,370	43,041
Inventory	229,814	139,386
Prepaid expenses and other current assets	62,746	44,324
Total current assets	4,787,995	1,603,196
Restricted cash	390,542	257,839
Property, plant, and equipment, net	169,586	74,549
Right of use assets related to finance leases, net	22,039	5,724
Right of use assets related to operating leases, net	167,907	117,016
Equipment related to power purchase agreements and fuel delivered to customers, net	78,711	75,807
Goodwill	71,856	72,387
Intangible assets, net	37,644	39,251
Other assets	13,820	5,513
Total assets	5,740,100	2,251,282
Current liabilities:
Accounts payable	68,378	50,198
Accrued expenses	52,645	46,083
Deferred revenue	35,463	23,275
Operating lease liabilities	23,284	14,314
Finance lease liabilities	2,758	903
Finance obligations	35,595	32,717
Current portion of long-term debt	23,491	25,389
Other current liabilities	28,329	29,487
Total current liabilities	269,943	222,366
Deferred revenue	63,402	32,944
Operating lease liabilities	139,400	99,624
Finance lease liabilities	17,027	4,493
Finance obligations	172,242	148,836
Convertible senior notes, net	192,320	85,640
Long-term debt	123,764	150,013
Other liabilities	55,113	40,447
Total liabilities	1,033,211	784,363
Stockholders' equity:
Common stock, $0.01 par value per share; 1,500,000,000 shares authorized; Issued (including shares in treasury): 593,077,995 at September 30, 2021 and 473,977,469 at December 31, 2020	5,930	4,740
Additional paid-in capital	6,978,454	3,446,650
Accumulated other comprehensive (loss) gain	(2,338)	2,451
Accumulated deficit	(2,203,989)	(1,946,488)
Less common stock in treasury: 17,032,648 at September 30, 2021 and 15,926,068 at December 31, 2020	(71,168)	(40,434)
Total stockholders' equity	4,706,889	1,466,919
Total liabilities and stockholders' equity	$ 5,740,100	$ 2,251,282

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Condensed Consolidated Balance Sheets
Debt Securities, Available-for-sale, Amortized Cost, Current	$ 756,841
Debt Securities, Available-for-sale, Allowance for Credit Loss, Current	$ 0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,500,000,000	1,500,000,000
Common stock, shares issued	593,077,995	473,977,469
Common stock in treasury, shares	17,032,648	15,926,068

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net revenue:
Net revenue	$ 143,922,000	$ 107,048,000	$ 340,437,000	$ 215,862,000
Cost of revenue:
Total cost of revenue	175,000,000	135,632,000	423,984,000	254,164,000
Gross loss	(31,078,000)	(28,584,000)	(83,547,000)	(38,302,000)
Operating expenses:
Research and development	16,634,000	7,386,000	37,623,000	17,033,000
Selling, general and administrative	42,421,000	17,210,000	106,652,000	49,963,000
Change in fair value of contingent consideration	8,530,000	1,130,000	8,760,000	1,130,000
Total operating expenses	67,585,000	25,726,000	153,035,000	68,126,000
Operating loss	(98,663,000)	(54,310,000)	(236,582,000)	(106,428,000)
Interest	(5,361,000)	(17,248,000)	(27,895,000)	(42,407,000)
Other expense, net	(50,000)	(303,000)	(318,000)	(452,000)
Realized loss on investments, net	(254,000)		(236,000)
Change in fair value of equity securities	(607,000)		(284,000)
Gain on extinguishment of debt				13,222,000
Loss on equity method investments	(1,736,000)		(1,736,000)
Loss before income taxes	(106,671,000)	(71,861,000)	(267,051,000)	(136,065,000)
Income tax benefit	0	6,644,000	0	24,015,000
Net loss attributable to the Company	(106,671,000)	(65,217,000)	(267,051,000)	(112,050,000)
Preferred stock dividends declared				(26,000)
Net loss attributable to common stockholders	$ (106,671,000)	$ (65,217,000)	$ (267,051,000)	$ (112,076,000)
Net loss per share:
Basic and diluted	$ (0.19)	$ (0.18)	$ (0.48)	$ (0.34)
Weighted average number of common stock outstanding	574,520,806	371,010,544	551,894,779	330,949,265
Sales of fuel cell systems and related infrastructure
Net revenue:
Net revenue	$ 115,999,000	$ 83,662,000	$ 262,049,000	$ 151,876,000
Cost of revenue:
Total cost of revenue	89,235,000	69,428,000	198,122,000	117,290,000
Services performed on fuel cell systems and related infrastructure
Net revenue:
Net revenue	6,677,000	6,829,000	18,397,000	19,586,000
Cost of revenue:
Total cost of revenue	18,697,000	9,180,000	47,258,000	27,300,000
Provision for loss contracts related to service
Cost of revenue:
Total cost of revenue	7,462,000	25,147,000	15,641,000	25,948,000
Power Purchase Agreements
Net revenue:
Net revenue	9,321,000	6,629,000	25,508,000	19,629,000
Cost of revenue:
Total cost of revenue	31,199,000	14,744,000	71,776,000	44,019,000
Fuel delivered to customers
Net revenue:
Net revenue	11,556,000	9,831,000	33,804,000	24,536,000
Cost of revenue:
Total cost of revenue	27,857,000	17,002,000	90,331,000	39,332,000
Other
Net revenue:
Net revenue	369,000	97,000	679,000	235,000
Cost of revenue:
Total cost of revenue	$ 550,000	$ 131,000	$ 856,000	$ 275,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Consolidated Statements of Comprehensive Loss
Net loss attributable to the Company	$ (106,671)	$ (65,217)	$ (267,051)	$ (112,050)
Foreign currency translation (loss) gain	(172)	687	(714)	558
Change in net unrealized loss on available-for-sale securities	(2,200)		(4,075)
Comprehensive loss attributable to the Company	(109,043)	(64,530)	(271,840)	(111,492)
Preferred stock dividends declared				(26)
Comprehensive loss attributable to common stockholders	$ (109,043)	$ (64,530)	$ (271,840)	$ (111,518)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock3.75% Convertible Senior Notes	Common Stock5.5% Convertible Senior Notes	Common Stock7.5% Convertible Senior Note	Common StockPrivate placement	Common Stock	Additional Paid-in-Capital3.75% Convertible Senior Notes	Additional Paid-in-Capital5.5% Convertible Senior Notes	Additional Paid-in-Capital7.5% Convertible Senior Note	Additional Paid-in-CapitalPrivate placement	Additional Paid-in-Capital	Accumulated Other Comprehensive Income	Treasury Stock	Accumulated Deficit	3.75% Convertible Senior Notes	5.5% Convertible Senior Notes	7.5% Convertible Senior Note	Private placement	Total
Balance at Dec. 31, 2019					$ 3,186					$ 1,506,953	$ 1,288	$ (31,216)	$ (1,350,307)					$ 129,904
Balance (in shares) at Dec. 31, 2019					318,637,560							15,259,045
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company													(112,050)					(112,050)
Other comprehensive (loss) gain											558							558
Stock-based compensation					$ 4					9,254								9,258
Stock-based compensation (in shares)					402,003
Stock dividend										20			(20)
Stock dividend (in shares)					5,156
Issuance of common stock, net					$ 353					344,045								344,398
Issuance of common stock, net (in shares)					35,276,250
Stock option exercises					$ 137					32,416								32,553
Stock option exercises (in shares)					13,736,265
Equity component of convertible senior notes, net of issuance costs and income tax (benefit) expense										108,479								108,479
Purchase of capped calls										(16,253)								(16,253)
Termination of capped calls										24,158								24,158
Stock exchanged for tax withholding												$ (9,218)						(9,218)
Stock exchanged for tax withholding (in shares)												667,023
Provision for common stock warrants										32,529								32,529
Accretion of discount, preferred stock										(29)								(29)
Conversion of preferred stock					$ 30					1,148								1,178
Conversion of preferred stock (in shares)					2,998,526
Conversion of Convertible Senior Notes			$ 160					$ 42,713								$ 42,873
Conversion of Convertible Senior Notes (in shares)			16,000,000
Repurchase of 5.5% Convertible Senior Notes, net of income tax benefit					$ 94					(51,840)								(51,746)
Repurchase of 5.5% Convertible Senior Notes, net of income tax benefit (in shares)					9,409,591
Shares issued for acquisitions					$ 97					49,576								49,673
Shares issued for acquisitions (in shares)					9,658,465
Balance at Sep. 30, 2020					$ 4,061					2,083,169	1,846	$ (40,434)	(1,462,377)					586,265
Balance (in shares) at Sep. 30, 2020					406,123,816							15,926,068
Balance (ASU 2020-06) at Dec. 31, 2020										(130,185)			9,550					(120,635)
Balance at Dec. 31, 2020					$ 4,740					3,446,650	2,451	$ (40,434)	(1,946,488)					$ 1,466,919
Balance (in shares) at Dec. 31, 2020					473,977,469							15,926,068						473,977,469
Increase (Decrease) in Stockholders' Equity
Net loss attributable to the Company													(267,051)					$ (267,051)
Other comprehensive (loss) gain											(4,789)							(4,789)
Stock-based compensation										34,813								34,813
Stock-based compensation (in shares)					61,408
Issuance of common stock, net				$ 549	$ 322				$ 1,564,088	2,022,871							$ 1,564,637	2,023,193
Issuance of common stock, net (in shares)				54,966,188	32,200,000
Stock option exercises					$ 46					5,270								5,316
Stock option exercises (in shares)					4,576,102
Stock exchanged for tax withholding												$ (30,734)						(30,734)
Stock exchanged for tax withholding (in shares)												1,106,580
Exercise of warrants					$ 242					15,203								15,445
Exercise of warrants (in shares)					24,210,984
Provision for common stock warrants										4,430								4,430
Conversion of Convertible Senior Notes	$ 30	$ 1				$ 15,155	$ 159							$ 15,185	$ 160
Conversion of Convertible Senior Notes (in shares)	3,016,036	69,808
Balance at Sep. 30, 2021					$ 5,930					$ 6,978,454	$ (2,338)	$ (71,168)	$ (2,203,989)					$ 4,706,889
Balance (in shares) at Sep. 30, 2021					593,077,995							17,032,648						593,077,995

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical)	Sep. 30, 2021	Jan. 31, 2021	Jan. 07, 2021	Jan. 01, 2021	Dec. 31, 2020	Sep. 30, 2020	May 31, 2020	May 29, 2020	May 18, 2020	Sep. 30, 2019	Mar. 31, 2018
Interest rate (as a percent)				3.75%
5.5% Convertible Senior Notes
Interest rate (as a percent)	5.50%	5.50%	5.50%		5.50%	5.50%	5.50%		5.50%	7.50%	5.50%
3.75% Convertible Senior Notes
Interest rate (as a percent)	3.75%						3.75%	3.75%	3.75%
7.5% Convertible Senior Note
Interest rate (as a percent)						7.50%				7.50%

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Operating Activities
Net loss attributable to the Company	$ (106,671)		$ (65,217)	$ (267,051)	$ (112,050)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of long-lived assets				15,903	9,860
Amortization of intangible assets	400		300	1,095	835
Stock-based compensation				34,813	9,258
Gain on extinguishment of debt					(13,222)
Amortization of debt issuance costs and discount on convertible senior notes				2,371	12,183
Provision for common stock warrants				4,746	25,198
Income tax benefit					(24,015)
Loss on service contracts				9,586	25,110
Fair value adjustment to contingent consideration				(8,760)	1,130
Impairment of long-lived assets				1,329
Net realized loss on investments	254			236
Lease origination costs				(7,889)
Change in fair value for equity securities	607			284
Loss on equity method investments	1,736			1,736
Changes in operating assets and liabilities that provide (use) cash:
Accounts receivable				(89,329)	(86,056)
Inventory				(90,428)	(57,615)
Prepaid expenses, and other assets				(28,465)	(4,956)
Accounts payable, accrued expenses, and other liabilities				28,992	41,125
Deferred revenue				42,330	16,709
Net cash used in operating activities				(348,501)	(156,506)
Investing Activities
Purchases of property, plant and equipment				(91,384)	(11,265)
Purchase of intangible assets					(1,638)
Purchases of equipment related to power purchase agreements and equipment related to fuel delivered to customers				(17,900)	(13,699)
Purchase of available-for-sale securities				(1,862,951)
Proceeds from sales and maturities of available-for-sale securities				1,105,874
Proceeds from sales of equity securities				21,780
Purchase of equity securities				(169,713)
Net cash paid for acquisition					(45,113)
Net cash used in investing activities				(1,014,294)	(71,715)
Financing Activities
Proceeds from exercise of warrants, net of transaction costs				15,445
Proceeds from public and private offerings, net of transaction costs				3,587,830	344,398
Payments of tax withholding on behalf of employees for net stock settlement of stock-based compensation				(30,734)	(9,218)
Proceeds from exercise of stock options				5,316	32,553
Proceeds from issuance of convertible senior notes, net					205,098
Repurchase of convertible senior notes					(90,238)
Purchase of capped calls and common stock forward					(16,253)
Proceeds from termination of capped calls					24,158
Principal payments on long-term debt				(29,129)	(27,845)
Proceeds from long-term debt, net					99,000
Repayments of finance obligations and finance leases				(20,413)	(19,038)
Proceeds from finance obligations				53,447	47,568
Net cash provided by financing activities				3,581,762	590,183
Effect of exchange rate changes on cash				(59)	(90)
Increase in cash, cash equivalents and restricted cash				2,218,908	361,872
Cash, cash equivalents, and restricted cash beginning of period		$ 731,372		1,634,284	369,500	$ 369,500
Cash, cash equivalents, and restricted cash end of period	$ 3,853,192	$ 1,634,284	$ 731,372	3,853,192	731,372	$ 1,634,284
Supplemental disclosure of cash flow information
Cash paid for interest, net capitalized interest of $2.6 million				10,341	16,975
Summary of non-cash activity
Recognition of right of use asset - finance leases				16,961
Recognition of right of use asset - operating leases				65,083	25,857
Conversion of preferred stock to common stock					$ 43,058
Conversion of convertible senior notes to common stock				15,345
Accrued purchase of fixed assets, cash to be paid in subsequent period				$ 8,832

Condensed Consolidated Statem_6

Condensed Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Condensed Consolidated Statements of Cash Flows
Net capitalized interest	$ 2.6

Nature of Operations

Nature of Operations	9 Months Ended
	Sep. 30, 2021
Nature of Operations
Nature of Operations	1. Nature of Operations ​ Plug Power is facilitating the paradigm shift to an increasingly electrified world by innovating cutting-edge hydrogen and fuel cell solutions. In our core business, we provide and continue to develop commercially viable hydrogen and fuel cell product solutions to replace lead-acid batteries in electric material handling vehicles and industrial trucks for some of the world’s largest retail-distribution and manufacturing businesses. We are focusing our efforts on industrial mobility applications, including electric forklifts and electric industrial vehicles, at multi-shift high volume manufacturing and high throughput distribution sites where we believe our products and services provide a unique combination of productivity, flexibility, and environmental benefits. Additionally, we manufacture and sell fuel cell products to replace batteries and diesel generators in stationary backup power applications. These products have proven valuable with telecommunications, transportation, and utility customers as robust, reliable, and sustainable power solutions. ​ Our current products and services include: GenDrive: GenDrive is our hydrogen fueled Proton Exchange Membrane (“PEM”) fuel cell system providing power to material handling electric vehicles, including class 1, 2, 3 and 6 electric forklifts, Automated Guided Vehicles (“AGVs”) and ground support equipment; GenFuel: GenFuel is our liquid hydrogen fueling delivery, generation, storage, and dispensing system; GenCare: GenCare is our ongoing ‘internet of things’-based maintenance and on-site service program for GenDrive fuel cell systems, GenSure fuel cell systems, GenFuel hydrogen storage and dispensing products and ProGen fuel cell engines; GenSure: GenSure is our stationary fuel cell solution providing scalable, modular PEM fuel cell power to support the backup and grid-support power requirements of the telecommunications, transportation, and utility sectors; GenSure High Power Fuel Cell Platform will support large scale stationary power and data center markets; GenKey: GenKey is our vertically integrated “turn-key” solution combining either GenDrive or GenSure fuel cell power with GenFuel fuel and GenCare aftermarket service, offering complete simplicity to customers transitioning to fuel cell power; ProGen: ProGen is our fuel cell stack and engine technology currently used globally in mobility and stationary fuel cell systems, and as engines in electric delivery vans. This includes the Plug Power membrane electrode assembly (“MEA”), a critical component of the fuel cell stack used in zero-emission fuel cell electric vehicle engines; and GenFuel Electrolyzers: GenFuel electrolyzers are modular, scalable hydrogen generators optimized for clean hydrogen production. We provide our products worldwide through our direct product sales force, and by leveraging relationships with original equipment manufacturers (“OEMs”) and their dealer networks. Plug Power is targeting Asia and Europe for expansion in adoption. Europe has rolled out ambitious targets for the hydrogen economy and Plug Power is executing on its strategy to become one of the European leaders. This includes a targeted account strategy for material handling as well as securing strategic partnerships with European OEMs, energy companies, utility leaders and accelerating our electrolyzer business. We manufacture our commercially viable products in Latham, New York, Rochester, New York and Spokane, Washington and support liquid hydrogen generation and logistics in Charleston, Tennessee. ​ Our wholly-owned subsidiary, Plug Power France, created a joint venture with Renault SAS (“Renault”) named HyVia, a French société par actions simplifiée (“HyVia”) in the second quarter 2021. HyVia plans to manufacture and sell fuel cell powered electric light commercial vehicles (“FCELCVs”) and to supply hydrogen fuel and fueling stations to support the FCE-LCV market, in each case primarily in Europe. HyVia is owned 50% by Plug Power France and 50% by Renault.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies ​ Restatement ​ As previously disclosed in the Explanatory Note to the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020 (the “2020 10-K”), the Company restated its previously issued audited consolidated financial statements as of and for the years ended December 31, 2019 and 2018 and its unaudited interim condensed consolidated financial statements as of and for each of the quarterly periods ended March 31, 2020 and 2019, June 30, 2020 and 2019, September 30, 2020 and 2019 and December 31, 2019. ​ Previously filed annual reports on Form 10-K and quarterly reports on Form 10-Q for the periods affected by the restatement have not been amended. Accordingly, investors should not rely upon the Company’s previously released financial statements for these periods and any earnings releases or other communications relating to these periods, and, for these periods, investors should rely solely on the financial statements and other financial data for the relevant periods included in the 2020 10-K. Commencing with our quarterly report on Form 10-Q for the quarterly period ended March 31, 2021, we are including in our quarterly reports for fiscal 2021 restated results for the corresponding interim periods of fiscal 2020. ​ Principles of Consolidation ​ The unaudited interim condensed consolidated financial statements include the financial statements of the Company and its wholly-owned subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. In addition, we include our share of the results of HyVia using the equity method based on our economic ownership interest and our ability to exercise significant influence over the operating and financial decisions of HyVia. ​ Interim Financial Statements ​ The accompanying unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). In the opinion of management, all adjustments, which consist solely of normal recurring adjustments, necessary to present fairly, in accordance with U.S. generally accepted accounting principles (“GAAP”), the financial position, results of operations and cash flows for all periods presented, have been made. The results of operations for the interim periods presented are not necessarily indicative of the results that may be expected for the full year. ​ Certain information and footnote disclosures normally included in annual consolidated financial statements prepared in accordance with GAAP have been condensed or omitted. These unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto included in the Company’s 2020 10-K. ​ The information presented in the accompanying unaudited interim condensed consolidated balance sheets as of December 31, 2020 has been derived from the Company’s December 31, 2020 audited consolidated financial statements. ​ Certain amounts in the prior period condensed consolidated financial statements have been reclassified to conform to the presentation of the current period condensed consolidated financial statements. ​ ​ There have been no changes in our accounting policies from those reported in our 2020 10-K, except for the adoption of 2020-06, as described in the Recently Adopted Accounting Guidance section. We have also expanded our accounting policy relating to cash equivalents, available-for-sale securities, equity securities, and stock-based compensation as follows: ​ Cash Equivalents ​ The Company considers all highly-liquid debt securities with original maturities of three months or less to be cash equivalents. At September 30, 2021, cash equivalents consisted of commercial paper and U.S. Treasury securities with original maturities of three months or less, and money market funds. Due to their short-term nature, the carrying amounts reported in the unaudited interim condensed consolidated balance sheets approximate the fair value of cash and cash equivalents. ​ Available-for-sale securities ​ Available-for-sale securities is comprised of commercial paper with original maturities greater than three months, U.S. Treasury securities, certificates of deposit and corporate bonds. We consider these securities to be ​ Available-for-sale securities are recorded at fair value as of each balance sheet date. As of each balance sheet date, unrealized gains and losses, with the exception of credit related losses, are recorded to accumulated other comprehensive income (loss). Any credit related losses are recognized as a credit loss allowance on the balance sheet with a corresponding adjustment to operations. Realized gains and losses are due to the sale and maturity of securities classified as available-for-sale and represent the net gain (loss) from accumulated other comprehensive income (loss) reclassifications for previously unrealized net gains on available-for-sale debt securities. ​ Equity securities ​ Equity securities are comprised of fixed income and equity market index mutual funds. Equity securities are valued at fair value with changes in the fair value recognized in our unaudited interim condensed consolidated statement of operations. We consider these securities to be ​ Stock-based compensation Stock-based compensation represents the cost related to stock-based awards granted to employees and directors. The Company measures stock-based compensation cost at grant date, based on the fair value of the award estimated under the current provisions of Accounting Standards Codification (“ASC”) Topic 718, Compensation - Stock Compensation. For service stock options and restricted stock awards, the Company estimates the fair value of stock-based awards using a Black-Scholes valuation model and recognizes the cost as expense on a straight-line basis over the option’s requisite service period. In September 2021, the Company also issued performance stock option awards that include a market condition. The grant date fair value of performance stock options is estimated using a Monte Carlo simulation model and the cost is recognized using the accelerated attribution method. Stock-based compensation expense is recorded in cost of revenue associated with sales of fuel cell systems and related infrastructure, cost of revenue for services performed on fuel cell systems and related infrastructure, research and development expense and selling, general and administrative expenses in the consolidated statements of operations based on the employees’ respective function. ​ Recent Accounting Pronouncements Recently Adopted Accounting Guidance ​ Other than the adoption of the accounting guidance mentioned i n our 2020 10-K and ASU 2020-06 On January 1, 2021, we early adopted ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) using the modified retrospective approach. Consequently, the Company’s 3.75% Convertible Senior Notes due 2025 (the “3.75% Convertible Senior Notes”) is now accounted for as a single liability measured at its amortized cost. This accounting change removed the impact of recognizing the equity component of the Company’s convertible notes at issuance and the subsequent accounting impact of additional interest expense from debt discount amortization. Future interest expense of the convertible notes will be lower as a result of adoption of this guidance and net loss per share will be computed using the if-converted method for convertible instruments. The cumulative effect of the accounting change upon adoption on January 1, 2021 increased the carrying amount of the 3.75% Convertible Senior Notes by $120.6 million, reduced accumulated deficit by $9.6 million and reduced additional paid-in capital by $130.2 million as of September 30, 2021. Recent Accounting Guidance Not Yet Effective ​ All issued but not yet effective accounting and reporting standards as of September 30, 2021 are either not applicable to the Company or are not expected to have a material impact on the Company. ​ ​

Extended Maintenance Contracts

Extended Maintenance Contracts	9 Months Ended
	Sep. 30, 2021
Extended Maintenance Contracts
Extended Maintenance Contracts	3. Extended Maintenance Contracts ​ On a quarterly basis, we evaluate any potential losses related to our extended maintenance contracts for fuel cell systems and related infrastructure that has been sold. We measure loss accruals at the customer contract level. The expected revenues and expenses for these contracts include all applicable expected costs of providing services over the remaining term of the contracts and the related unearned net revenue. A loss is recognized if the sum of expected costs of providing services under the remaining term of the contract exceeds related unearned net revenue and is recorded as a provision for loss contracts related to service in the consolidated statements of operations. A key component of these estimates is the expected future service costs. In estimating the expected future costs, the Company considers its current service cost level and applies significant judgment related to expected cost saving initiatives. The expected future cost savings will be primarily dependent upon the success of the Company’s initiatives related to increasing stack life, achieving better economies of scale for service labor, and improvements in design and operations of infrastructure. If the expected cost saving initiatives are not realized, this will increase the estimated costs of providing services and will adversely affect our estimated contract loss accrual. Further, we continue to work to improve quality and reliability; however, unanticipated additional quality issues or warranty claims may arise and additional material charges may be incurred in the future. These quality issues could also adversely affect our contract loss accrual. Service costs during 2021 have been higher than previously estimated. The Company has undertaken or will soon undertake several initiatives to extend the life and improve the reliability of its equipment. As a result of these initiatives and our additional expectation that the increase in certain costs attributable to the global pandemic will abate, the Company believes that its contract loss accrual is sufficient. However, if elevated service costs persist, the Company will adjust its estimated future service costs and increase its contract loss accrual estimate. ​ The following table shows the rollforward of balance in the accrual for loss contracts, including changes due to the passage of time, additions, and changes in estimates (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Year ended ​ September 30, 2021 ​ December 31, 2020 Beginning Balance $ 24,013 ​ $ 3,702 Provision for Loss Accrual ​ 15,641 ​ ​ 35,473 Released to Service Cost of Sales ​ (6,055) ​ ​ (2,348) Released to Provision for Warrants ​ — ​ ​ (12,814) Ending Balance $ 33,599 ​ $ 24,013 ​

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share
Earnings Per Share	4. Earnings Per Share ​ Basic earnings per common stock are computed by dividing net loss attributable to common stockholders by the weighted average number of common stock outstanding during the reporting period. After January 1, 2021, the date of the adoption of ASU 2020-06, in periods when we have net income, the shares of our common stock subject to the convertible notes outstanding during the period will be included in our diluted earnings per share under the if-converted method. Since the Company is in a net loss position, all common stock equivalents would be considered anti-dilutive and are therefore not included in the determination of diluted earnings per share. Accordingly, basic and diluted loss per share are the same. ​ The potentially dilutive securities are summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ At September 30, ​ 2021 2020 Stock options outstanding (1) ​ 24,784,288 14,434,983 Restricted stock outstanding (2) ​ 4,960,376 5,992,974 Common stock warrants (3) ​ 80,017,181 ​ 110,573,392 Convertible Senior Notes (4) ​ 39,170,766 56,872,730 Number of dilutive potential shares of common stock ​ 148,932,611 187,874,079 ​ (1) During the three months ended September 30, 2021 and 2020, the Company granted 15,732,335 and 3,192,400 stock options, respectively. During the nine months ended September 30, 2021 and 2020, the Company granted 16,430,835 and 3,367,049 stock options, respectively. ​ (2) During the three months ended September 30, 2021 and 2020, the Company granted 1,159,856 and 3,095,000 shares of restricted stock, respectively. During the nine months ended September 30, 2021 and 2020, the Company granted 1,812,856 and 3,189,649 shares of restricted stock, respectively. ​ (3) In April 2017, the Company issued a warrant to acquire up to 55,286,696 shares of the Company’s common stock as part of a transaction agreement with Amazon, subject to certain vesting events, as described in Note 12, “Warrant Transaction Agreements.” The warrant had been exercised with respect to 17,461,994 shares of the Company’s common stock as of September 30, 2021. ​ In July 2017, the Company issued a warrant to acquire up to 55,286,696 shares of the Company’s common stock as part of a transaction agreement with Walmart, subject to certain vesting events, as described in Note 12, “Warrant Transaction Agreements.” The warrant had been exercised with respect to 13,094,217 shares of the Company’s common stock as of September 30, 2021. ​ (4) In March 2018, the Company issued $100.0 million in aggregate principal amount of the 5.5% Convertible Senior Notes due 2023 (the “5.5% Convertible Senior Notes”). In May 2020, the Company repurchased $66.3 million of the 5.5% Convertible Senior Notes and in the fourth quarter of 2020, $33.5 million of the 5.5% Convertible Senior Notes were converted into approximately 14.6 million shares of common stock. The remaining $160 thousand aggregate principal amount of the 5.5% Convertible Senior Notes were converted into 69,808 shares of common stock in January 2021. In September 2019, the Company issued $40.0 million in aggregate principal amount of the 7.5% Convertible Senior Note due 2023 (the “7.5% Convertible Senior Note”), which was fully converted into 16.0 million shares of common stock on July 1, 2020. In May 2020, the Company issued $212.5 million in aggregate principal amount of the 3.75% Convertible Senior Notes. During the first quarter of 2021, $15.2 million of the 3.75% Convertible Senior Notes were converted into 3,016,036 shares of common stock. There were no conversions in the second or third quarter of 2021.

Inventory

Inventory	9 Months Ended
	Sep. 30, 2021
Inventory
Inventory	​ 5. Inventory ​ Inventory as of September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 ​ 2020 ​ Raw materials and supplies - production locations ​ $ 147,085 ​ $ 92,221 ​ Raw materials and supplies - customer locations ​ ​ 13,611 ​ ​ 12,405 ​ Work-in-process ​ 61,525 ​ 29,349 ​ Finished goods ​ 7,593 ​ 5,411 ​ Inventory ​ $ 229,814 ​ $ 139,386 ​ ​

Equipment Related to Power Purc

Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net	9 Months Ended
	Sep. 30, 2021
Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net
Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net	​ 6. Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net ​ Equipment related to power purchase agreements and fuel delivered to customers, net at September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 ​ 2020 Equipment related to power purchase agreements and fuel delivered to customers ​ $ 99,230 ​ $ 92,736 ​ Less: accumulated depreciation ​ ​ (20,519) ​ ​ (16,929) ​ Equipment related to power purchase agreements and fuel delivered to customers, net ​ ​ 78,711 ​ ​ 75,807 ​ ​ As of September 30, 2021, the Company had deployed long-lived assets at customer sites that had associated Power Purchase Agreements (“PPAs”). These PPAs expire over the next one ​ Depreciation expense was $1.9 million and $2.3 million for the three months ended September 30, 2021 and 2020, respectively. Depreciation expense was $5.7 million and $6.6 million for the nine months ended September 30, 2021 and 2020, respectively. ​ The Company terminated its contractual relationship with a fuel provider effective March 31, 2021. The Company has historically leased fuel tanks from this provider. As a result of this termination, the Company recognized approximately $16.0 million of various costs in the six months ended June 30, 2021, primarily for removal of tanks, reimbursement of unamortized installation costs, costs to temporarily provide customers with fuel during the transition period, and certain other contract settlement costs, which were recorded in the Company’s unaudited interim condensed consolidated statement of operations as cost of revenue – fuel delivered to customers. The Company also purchased certain fuel tanks from the fuel provider during the six months ended June 30, 2021. No such purchases were made during the three months ended September 30, 2021.

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment
Property, Plant and Equipment	7. Property, Plant and Equipment ​ Property, plant and equipment at September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ December 31, 2020 Land ​ ​ 1,165 ​ ​ 1,165 Leasehold improvements ​ $ 1,440 ​ $ 1,121 Construction in progress ​ ​ 100,136 ​ ​ 15,590 Software, machinery, and equipment ​ 94,200 ​ 78,859 Property, plant, and equipment ​ 196,941 ​ 96,735 Less: accumulated depreciation ​ (27,355) ​ (22,186) Property, plant, and equipment, net ​ $ 169,586 ​ $ 74,549 ​ Construction in progress is primarily comprised of construction of hydrogen production plants and the Gigafactory in Rochester. Completed assets are transferred to their respective asset classes, and depreciation begins when an asset is ready for its intended use. Interest on outstanding debt is capitalized during periods of capital asset construction and amortized over the useful lives of the related assets. During the nine months ended September 30, 2021, we capitalized $2.6 million of interest. Capitalized interest in 2020 was not significant. ​ Depreciation expense related to property, plant and equipment was $1.9 million and $1.4 million for the three months ended September 30, 2021 and 2020, respectively. Depreciation expense related to property, plant and equipment was $5.2 million and $3.2 million for the nine months ended September 30, 2021 and 2020, respectively.

Intangible Assets and Goodwill

Intangible Assets and Goodwill	9 Months Ended
	Sep. 30, 2021
Intangible Assets and Goodwill
Intangible Assets and Goodwill	8. Intangible Assets and Goodwill ​ The gross carrying amount and accumulated amortization of the Company’s acquired identifiable intangible assets as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ Gross Carrying ​ Accumulated ​ ​ ​ ​ ​ ​ Amortization Period ​ Amount ​ Amortization ​ Total Acquired technology 10 years $ 13,040 ​ $ (4,888) ​ $ 8,152 ​ Customer relationships, Non-compete agreements, Backlog & Trademark ​ 6 years ​ 890 ​ ​ (398) ​ ​ 492 ​ In process research and development Indefinite ​ ​ 29,000 ​ ​ — ​ ​ 29,000 ​ ​ ​ ​ ​ $ 42,930 ​ $ (5,286) ​ $ 37,644 ​ ​ The gross carrying amount and accumulated amortization of the Company’s acquired identifiable intangible assets as of December 31, 2020 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ Gross Carrying ​ Accumulated ​ ​ ​ ​ ​ ​ Amortization Period ​ Amount ​ Amortization ​ Total Acquired technology 10 years ​ $ 13,697 ​ $ (4,042) ​ $ 9,655 ​ Customer relationships, Non-compete agreements, Backlog & Trademark ​ 6 years ​ ​ 890 ​ ​ (294) ​ ​ 596 ​ In process research and development Indefinite ​ 29,000 ​ ​ — ​ 29,000 ​ ​ ​ ​ ​ $ 43,587 ​ $ (4,336) ​ $ 39,251 ​ ​ The change in the gross carrying amount of the acquired technology from December 31, 2020 to September 30, 2021 was primarily due to foreign currency translation. ​ Amortization expense for acquired identifiable intangible assets for the three months ended September 30, 2021 and 2020 was $0.4 million and $0.3 million, respectively. Amortization expense for acquired identifiable intangible assets for the nine months ended September 30, 2021 and 2020 was $1.1 million and $0.8 million, respectively. ​ The estimated amortization expense for subsequent years is as follows (in thousands): ​ ​ ​ ​ ​ Remainder of 2021 $ 363 2022 ​ ​ 1,453 2023 ​ ​ 1,453 2024 ​ ​ 1,431 2025 and thereafter ​ ​ 3,944 Total ​ $ 8,644 ​ Goodwill was $71.9 million and $72.4 million as of September 30, 2021 and December 31, 2020, respectively, which decreased $531 thousand due to currency translation loss for HyPulsion S.A.S., our French subsidiary. There were no impairments during the nine months ended September 30, 2021 or the year ended December 31, 2020.

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2021
Long-Term Debt
Long-Term Debt	9. Long-Term Debt ​ In March 2019, the Company entered into a loan and security agreement, as amended (the “Loan Agreement”), with Generate Lending, LLC (“Generate Capital”), providing for a secured term loan facility in the amount of $100 million (the “Term Loan Facility”). ​ During the year ended December 31, 2020, the Company, under another series of amendments to the Loan Agreement, borrowed an incremental $100.0 million. As part of the amendment to the Loan Agreement, the Company’s interest rate on the secured term loan facility was reduced to 9.50% from 12.00% per annum, and the maturity date was extended to October 31, 2025 from October 6, 2022. On September 30, 2021, the outstanding balance under the Term Loan Facility was $137.7 million. In addition to the Term Loan Facility, on September 30, 2021, there was approximately $9.5 million of debt outstanding related to the United Hydrogen Group, Inc. acquisition. ​ The Loan Agreement includes covenants, limitations, and events of default customary for similar facilities. Interest and a portion of the principal amount is payable on a quarterly basis. Principal payments are funded in part by releases of restricted cash, as described in Note 19, “Commitments and Contingencies.” Based on the amortization schedule as of September 30, 2021, the aforementioned loan balance under the Term Loan Facility will be fully paid by October 31, 2025. The Company is in compliance with, or has obtained waivers for, all debt covenants. ​ The Term Loan Facility is secured by substantially all of the Company’s and the guarantor subsidiaries’ assets, including, among other assets, all intellectual property, all securities in domestic subsidiaries and 65% of the securities in foreign subsidiaries, subject to certain exceptions and exclusions. ​ The Loan Agreement provides that if there is an event of default due to the Company’s insolvency or if the Company fails to perform in any material respect the servicing requirements for fuel cell systems under certain customer agreements, which failure would entitle the customer to terminate such customer agreement, replace the Company or withhold the payment of any material amount to the Company under such customer agreement, then Generate Capital has the right to cause Proton Services Inc., a wholly owned subsidiary of the Company, to replace the Company in performing the maintenance services under such customer agreement. ​ As of September 30, 2021, the Term Loan Facility requires the principal balance as of each of the following dates not to exceed the following (in thousands): ​ ​ ​ ​ December 31, 2021 $ 127,317 December 31, 2022 ​ 93,321 December 31, 2023 ​ 62,920 December 31, 2024 ​ 33,692 December 31, 2025 ​ — ​

Convertible Senior Notes

Convertible Senior Notes	9 Months Ended
	Sep. 30, 2021
Convertible Senior Notes.
Convertible Senior Notes	​ 10. Convertible Senior Notes ​ 3.75% Convertible Senior Notes ​ On May 18, 2020, the Company issued $200.0 million in aggregate principal amount of 3.75% Convertible Senior Notes due June 1, 2025, in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”). On May 29, 2020, the Company issued an additional $12.5 million in aggregate principal amount of 3.75% Convertible Senior Notes. ​ At issuance in May 2020, the total net proceeds from the 3.75% Convertible Senior Notes were as follows: ​ ​ ​ ​ ​ Amount ​ (in thousands) Principal amount $ 212,463 Less initial purchasers' discount ​ (6,374) Less cost of related capped calls ​ (16,253) Less other issuance costs ​ (617) Net proceeds $ 189,219 ​ The 3.75% Convertible Senior Notes bear interest at a rate of 3.75% per year, payable semi-annually in arrears on June 1 and December 1 of each year, beginning on December 1, 2020. The notes will mature on June 1, 2025, unless earlier converted, redeemed or repurchased in accordance with their terms. ​ The 3.75% Convertible Senior Notes are senior, unsecured obligations of the Company and rank senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the notes, equal in right of payment to any of the Company’s existing and future liabilities that are not so subordinated, including the Company’s $100 million in aggregate principal amount of the 5.5% Convertible Senior Notes, effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the collateral securing such indebtedness, and structurally subordinated to all indebtedness and other liabilities, including trade payables, of its current or future subsidiaries. ​ Holders of the 3.75% Convertible Senior Notes may convert their notes at their option at any time prior to the close of the business day immediately preceding December 1, 2024 in the following circumstances: ​ 1) during any calendar quarter commencing after March 31, 2021 if the last reported sale price of the Company’s common stock exceeds 130% of the conversion price for each of at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter; ​ 2) during the five business days after any five consecutive trading day period (such five consecutive trading day period, the measurement period) in which the trading price per $1,000 principal amount of the 3.75% Convertible Senior Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; ​ 3) if the Company calls any or all of the 3.75% Convertible Senior Notes for redemption, any such notes that have been called for redemption may be converted at any time prior to the close of business on the second scheduled trading day immediately preceding the redemption date; or ​ 4) upon the occurrence of specified corporate events, as described in the indenture governing the 3.75% Convertible Senior Notes. ​ On or after December 1, 2024, the holders of the 3.75% Convertible Senior Notes may convert all or any portion of their notes at any time prior to the close of business on the second scheduled trading day immediately preceding the maturity date regardless of the foregoing conditions. ​ The initial conversion rate for the 3.75% Convertible Senior Notes is 198.6196 shares of the Company’s common stock per $1,000 principal amount of notes, which is equivalent to an initial conversion price of approximately $5.03 per share of the Company’s common stock, subject to adjustment upon the occurrence of specified events. Upon conversion, the Company will pay or deliver, as applicable, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. During the three months ended September 30, 2021, certain conditions allowing holders of the 3.75% Convertible Senior Notes to convert were met. The 3.75% Convertible Senior Notes are therefore convertible during the calendar quarter ending September 30, 2021 at the conversion rate discussed above. During the nine months ended September 30, 2021, $15.2 million of the 3.75% Convertible Senior Notes were converted and the Company issued approximately 3.0 million shares of common stock in conjunction with these conversions. ​ In addition, following certain corporate events or following issuance of a notice of redemption, the Company will increase the conversion rate for a holder who elects to convert its notes in connection with such a corporate event or convert its notes called for redemption during the related redemption period in certain circumstances. ​ The 3.75% Convertible Senior Notes will be redeemable, in whole or in part, at the Company’s option at any time, and from time to time, on or after June 5, 2023 and before the 41 st one three ​ If the Company undergoes a “fundamental change” (as defined in the Indenture), holders may require the Company to repurchase their notes for cash all or any portion of their notes at a fundamental change repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest, to, but excluding, the fundamental change repurchase date. ​ The Company accounts for the 3.75% Convertible Senior Notes as a liability. We incurred transaction costs related to the issuance of the 3.75% Convertible Senior Notes of approximately $7.0 million, consisting of initial purchasers’ discount of approximately $6.4 million and other issuance costs of $0.6 million which were recorded as debt issuance cost (presented as contra debt in the unaudited interim condensed consolidated balance sheets) and are being amortized to interest expense over the term of the 3.75% Convertible Senior Notes. The 3.75% Convertible Senior Notes consisted of the following (in thousands): ​ ​ ​ ​ ​ September 30, ​ 2021 Principal amounts: ​ ​ Principal $ 197,278 Unamortized debt issuance costs (1) ​ (4,958) Net carrying amount $ 192,320 1) Included in the unaudited interim condensed consolidated balance sheets within the 3.75% Convertible Senior Notes, net and amortized over the remaining life of the notes using the effective interest rate method. ​ The following table summarizes the total interest expense and effective interest rate related to the 3.75% Convertible Senior Notes (in thousands, except for effective interest rate): ​ ​ ​ ​ ​ ​ September 30, ​ 2021 Interest expense $ 1,849 Amortization of debt issuance costs ​ 306 Total ​ 2,155 ​ ​ ​ Effective interest rate ​ 4.50% ​ ​ Capped Call ​ In conjunction with the pricing of the 3.75% Convertible Senior Notes, the Company entered into privately negotiated capped call transactions (the “3.75% Notes Capped Call”) with certain counterparties at a price of $16.2 million. The 3.75% Notes Capped Call covers, subject to anti-dilution adjustments, the aggregate number of shares of the Company’s common stock that underlie the initial 3.75% Convertible Senior Notes and The net cost incurred in connection with the 3.75% Notes Capped Call were recorded as a reduction to additional paid-in capital in the unaudited interim condensed consolidated balance sheets. 5.5% Convertible Senior Notes ​ In March 2018, the Company issued $100.0 million in aggregate principal amount of the 5.5% Convertible Senior Notes due on March 15, 2023, in a private placement to qualified institutional buyers pursuant to Rule 144A under the Securities Act. ​ In May 2020, the Company used a portion of the net proceeds from the issuance of the 3.75% Convertible Senior Notes to finance the cash portion of the partial repurchase of the 5.5% Convertible Senior Notes, which consisted of a repurchase of approximately $66.3 million in aggregate principal amount of the 5.5% Convertible Senior Notes in privately-negotiated transactions for aggregate consideration of $128.9 million, consisting of approximately $90.2 million in cash and approximately 9.4 million shares of the Company’s common stock. The partial repurchase of the 5.5% Convertible Senior Notes resulted in a $13.2 million gain on early debt extinguishment. In the fourth quarter of 2020, $33.5 million of the remaining 5.5% Convertible Senior Notes were converted into 14.6 million shares of common stock which resulted in a gain of approximately $4.5 million which was recorded on the consolidated statement of operations on the gain (loss) on extinguishment of debt line. ​ On January 7, 2021, the remaining aggregate principal of $160 thousand aggregate principal amount of the 5.5% Convertible Senior Notes were converted into 69,808 shares of common stock. Interest expense and amortization for the period were immaterial. ​ Capped Call ​ In conjunction with the pricing of the 5.5% Convertible Senior Notes, the Company entered into privately negotiated capped call transactions (the “5.5% Notes Capped Call”) with certain counterparties at a price of $16.0 million to reduce the potential dilution to the Company’s common stock upon any conversion of the 5.5% Convertible Senior Notes and/or offset any cash payments the Company is required to make in excess of the principal amount of the converted 5.5% Convertible Senior Notes, as the case may be. The net cost incurred in connection with the 5.5% Notes Capped Call has been recorded as a reduction to additional paid-in capital in the unaudited interim condensed consolidated balance sheets. ​ In conjunction with the pricing of the partial repurchase of the 5.5% Convertible Senior Notes, the Company terminated 100% of the 5.5% Notes Capped Call on June 5, 2020. As a result of the termination, the Company received $24.2 million, which was recorded in additional paid-in capital in the unaudited interim condensed consolidated balance sheets. ​ Common Stock Forward ​ In connection with the issuance of the 5.5% Convertible Senior Notes, the Company also entered into a forward stock purchase transaction (the “Common Stock Forward”), pursuant to which the Company agreed to purchase 14,397,906 shares of its common stock for settlement on or about March 15, 2023. In connection with the issuance of the 3.75% Convertible Senior Notes and the partial repurchase of the 5.5% Convertible Senior Notes, the Company amended and extended the maturity of the Common Stock Forward to June 1, 2025. The number of shares of common stock that the Company will ultimately repurchase under the Common Stock Forward is subject to customary anti-dilution adjustments. The Common Stock Forward is subject to early settlement or settlement with alternative consideration in the event of certain corporate transactions. ​ The net cost incurred in connection with the Common Stock Forward of $27.5 million was recorded as an increase in treasury stock in the unaudited interim condensed consolidated balance sheets. The related shares were accounted for as a repurchase of common stock. ​ The book value of the 5.5% Notes Capped Call and Common Stock Forward are not remeasured. ​ During the fourth quarter of 2020, the Common Stock Forward was partially settled and, as a result, the Company received 4.4 million shares of its common stock. During the three months ended September 30, 2021, 0 shares were settled and received by the Company. During the nine months ended September 30, 2021, 8.1 million shares were settled and received by the Company.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity
Stockholders' Equity	11. Stockholders’ Equity ​ Preferred Stock ​ The Company has authorized 5.0 million shares of preferred stock, par value $0.01 per share. The Company’s certificate of incorporation provides that shares of preferred stock may be issued from time to time in one or more series. The Company’s Board of Directors is authorized to fix the voting rights, if any, designations, powers, preferences, qualifications, limitations and restrictions thereof, applicable to the shares of each series. ​ The Company has authorized Series A Junior Participating Cumulative Preferred Stock, par value $0.01 per share. As of September 30, 2021 and December 31, 2020, there were no shares of Series A Junior Participating Cumulative Preferred Stock issued and outstanding. ​ Common Stock and Warrants ​ The Company has one class of common stock, par value $0.01 per share. Each share of the Company’s common stock is entitled to one vote on all matters submitted to stockholders. ​ In February 2021, the Company completed the previously announced sale of its common stock in connection with a strategic partnership with SK Holdings Co., Ltd. (“SK Holdings”) to accelerate the use of hydrogen as an alternative energy source in Asian markets. The Company sold 54,966,188 shares of its common stock to a subsidiary of SK Holdings at a purchase price of $29.2893 per share, or an aggregate purchase price of approximately $1.6 billion. ​ In January and February 2021, the Company issued and sold in a registered equity offering an aggregate of 32.2 million shares of its common stock at a purchase price of $65.00 per share for net proceeds of approximately $2.0 billion. ​ In November 2020, the Company issued and sold in a registered equity offering an aggregate of 43,700,000 shares of its common stock at a purchase price of $22.25 per share for net proceeds of approximately $927.3 million. ​ In August 2020, the Company issued and sold in a registered equity offering an aggregate of 35,276,250 shares of its common stock at a purchase price of $10.25 per share for net proceeds of approximately $344.4 million. ​ During 2017, warrants to purchase up to 110,573,392 shares of common stock were issued in connection with transaction agreements with Amazon and Walmart, as discussed in Note 12, “Warrant Transaction Agreements.” At both September 30, 2021 and December 31, 2020, a total of 68,380,913 warrants had vested. Warrants were exercised with respect to 5,819,652 shares during the fourth quarter of 2020. For the three and nine months ended September 30, 2021, warrants were exercised with respect to 3,501,640 and 24,736,559 shares of common stock, respectively. These warrants are measured at fair value at the time of grant or modification and are classified as equity instruments on the unaudited interim condensed consolidated balance sheets. ​ At Market Issuance Sales Agreement ​ On April 13, 2020, the Company entered into the At Market Issuance Sales Agreement with B. Riley Financial (“B. Riley”), as sales agent, pursuant to which the Company may offer and sell, from time to time through B. Riley, shares of Company common stock having an aggregate offering price of up to $75.0 million. As of the date of this filing, the Company has not issued any shares of common stock pursuant to the At Market Issuance Sales Agreement.

Warrant Transaction Agreements

Warrant Transaction Agreements	9 Months Ended
	Sep. 30, 2021
Warrant Transaction Agreements
Warrant Transaction Agreements	12. Warrant Transaction Agreements ​ Amazon Transaction Agreement ​ On April 4, 2017, the Company and Amazon entered into a Transaction Agreement (the “Amazon Transaction Agreement”), pursuant to which the Company agreed to issue to Amazon.com NV Investment Holdings LLC, a wholly owned subsidiary of Amazon, a warrant (the “Amazon Warrant”) to acquire up to 55,286,696 shares of the Company’s common stock (the “Amazon Warrant Shares”), subject to certain vesting events described below. The Company and Amazon entered into the Amazon Transaction Agreement in connection with existing commercial agreements between the Company and Amazon with respect to the deployment of the Company’s GenKey fuel cell technology at Amazon distribution centers. The existing commercial agreements contemplate, but do not guarantee, future purchase orders for the Company’s fuel cell technology. The vesting of the Amazon Warrant Shares was conditioned upon payments made by Amazon or its affiliates (directly or indirectly through third parties) pursuant to the existing commercial agreements. ​ Under the terms of the original Amazon Warrant, the first tranche of the 5,819,652 Amazon Warrant Shares vested upon execution of the Amazon Warrant, and the remaining Amazon Warrant Shares vest based on Amazon’s payment of up to $600.0 million to the Company in connection with Amazon’s purchase of goods and services from the Company. The $6.7 million fair value of the first tranche of the Amazon Warrant Shares was recognized as selling, general and administrative expense upon execution of the Amazon Warrant. ​ Provision for the second and third tranches of Amazon Warrant Shares is recorded as a reduction of revenue because they represent consideration payable to a customer. ​ The fair value of the second tranche of Amazon Warrant Shares was measured at January 1, 2019, upon adoption of ASU 2019-08. The second tranche of 29,098,260 Amazon Warrant Shares vested in four equal installments, as Amazon or its affiliates, directly or indirectly through third parties, made an aggregate of $50.0 million in payments for goods and services to the Company, up to payments totaling $200.0 million in the aggregate. The last installment of the second tranche vested on November 2, 2020. Revenue reductions of $9.0 million, $4.1 million and $9.8 million associated with the second tranche of Amazon Warrant Shares were recorded in 2020, 2019 and 2018, respectively, under the terms of the original Amazon Warrant. ​ Under the terms of the original Amazon Warrant, the third tranche of 20,368,784 Amazon Warrant Shares vests in eight equal installments, as Amazon or its affiliates, directly or indirectly through third parties, made an aggregate of $50.0 million in payments for goods and services to the Company, up to payments totaling $400.0 million in the aggregate. The measurement date for the third tranche of Amazon Warrant Shares was November 2, 2020, when their exercise price was determined, as discussed further below. The fair value of the third tranche of Amazon Warrant Shares was determined to be $10.57 each. During 2020, revenue reductions of $24.1 million associated with the third tranche Amazon Warrant Shares were recorded under the terms of the original Amazon Warrant, prior to the December 31, 2020 waiver described below. On December 31, 2020, the Company waived the remaining vesting conditions under the Amazon Warrant, which resulted in the immediate vesting of all the third tranche of the Amazon Warrant Shares and recognition of an additional $399.7 million reduction to revenue. ​ The $399.7 million reduction to revenue resulting from the December 31, 2020 waiver was determined based upon a probability assessment of whether the underlying shares would have vested under the terms of the original Amazon Warrant. Based upon the Company’s projections of probable future cash collections from Amazon (i.e., a Type I share based payment modification), a reduction of revenue associated with 5,354,905 Amazon Warrant Shares was recognized at their previously measured November 2, 2020 fair value of $10.57 per warrant. A reduction of revenue associated with the remaining 12,730,490 Amazon Warrant Shares was recognized at their December 31, 2020 fair value of $26.95 each, based upon the Company’s assessment that associated future cash collections from Amazon were not deemed probable (i.e., a Type III share based payment modification). ​ The $399.7 million reduction to revenue was recognized during the year ended December 31, 2020 because the Company concluded such amount was not recoverable from the margins expected from future purchases by Amazon under the Amazon Warrant, and no exclusivity or other rights were conferred to the Company in connection with the December 31, 2020 waiver. Additionally, for the year ended December 31, 2020, the Company recorded a reduction to the provision for warrants of $12.8 million in connection with the release of the service loss accrual. ​ At December 31, 2020, all 55,286,696 of the Amazon Warrant Shares had vested. For service contracts entered into prior to December 31, 2020, the warrant charge associated with that revenue was capitalized and is subsequently amortized over the life of the service contract. The total amount of provision for common stock warrants recorded as a reduction of revenue for the Amazon Warrant during the three months ended September 30, 2021 and 2020 was $106 ​ The exercise price for the first and second tranches of Amazon Warrant Shares was $1.1893 per share. The exercise price of the third tranche of Amazon Warrant Shares was $13.81 per share, which was determined pursuant to the terms of the Amazon Warrant as an amount equal to ninety percent (90%) of the 30-day volume weighted average share price of the Company’s common stock as of November 2, 2020, the final vesting date of the second tranche of Amazon Warrant Shares. The Amazon Warrant is exercisable through April 4, 2027. The Amazon Warrant provides for net share settlement that, if elected by the holder, will reduce the number of shares issued upon exercise to reflect net settlement of the exercise price. The Amazon Warrant provides for certain adjustments that may be made to the exercise price and the number of shares of common stock issuable upon exercise due to customary anti-dilution provisions based on future events. The Amazon Warrant is classified as an equity instrument. ​ Fair value of the Amazon Warrant at December 31, 2020 and November 2, 2020 was based on the Black Scholes Option Pricing Model, which is based, in part, upon level 3 unobservable inputs for which there is little or no market data, requiring the Company to develop its own assumptions. ​ The Company used the following assumptions for its Amazon Warrant: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ November 2, 2020 Risk-free interest rate ​ 0.58% ​ 0.58% Volatility ​ 75.00% ​ 75.00% Expected average term ​ 6.26 ​ 6.42 Exercise price ​ $13.81 ​ $13.81 Stock price ​ $33.91 ​ $15.47 ​ Walmart Transaction Agreement ​ On July 20, 2017, the Company and Walmart entered into a Transaction Agreement (the “Walmart Transaction Agreement”), pursuant to which the Company agreed to issue to Walmart a warrant (the “Walmart Warrant”) to acquire up to 55,286,696 shares of the Company’s common stock, subject to certain vesting events (the “Walmart Warrant Shares”). The Company and Walmart entered into the Walmart Transaction Agreement in connection with existing commercial agreements between the Company and Walmart with respect to the deployment of the Company’s GenKey fuel cell technology across various Walmart distribution centers. The existing commercial agreements contemplate, but do not guarantee, future purchase orders for the Company’s fuel cell technology. The vesting of the warrant shares conditioned upon payments made by Walmart or its affiliates (directly or indirectly through third parties) pursuant to transactions entered into after January 1, 2017 under existing commercial agreements. ​ The majority of the Walmart Warrant Shares will vest based on Walmart’s payment of up to $600.0 million to the Company in connection with Walmart’s purchase of goods and services from the Company. The first tranche of 5,819,652 Walmart Warrant Shares vested upon the execution of the Walmart Warrant and was fully exercised as of December 31, 2020. Accordingly, $10.9 million, the fair value of the first tranche of Walmart Warrant Shares, was recorded as a provision for common stock warrants and presented as a reduction to revenue on the consolidated statements of operations during 2017. All future provision for common stock warrants is measured based on their grant-date fair value and recorded as a charge against revenue. The second tranche of 29,098,260 Walmart Warrant Shares vests in four installments of 7,274,565 Walmart Warrant Shares each time Walmart or its affiliates, directly or indirectly through third parties, make an aggregate of $50.0 million in payments for goods and services to the Company, up to payments totaling $200.0 million in the aggregate. The exercise price for the first and second tranches of Walmart Warrant Shares is $2.1231 per share. After Walmart has made payments to the Company totaling $200.0 million, the third tranche of 20,368,784 Walmart Warrant Shares will vest in eight installments of 2,546,098 Walmart Warrant Shares each time Walmart or its affiliates, directly or indirectly through third parties, make an aggregate of $50.0 million in payments for goods and services to the Company, up to payments totaling $400.0 million in the aggregate. The exercise price of the third tranche of Walmart Warrant Shares will be an amount per share equal to ninety percent (90%) of the 30-day volume weighted average share price of the common stock as of the final vesting date of the second tranche of Walmart Warrant Shares, provided that, with limited exceptions, the exercise price for the third tranche will be no lower than $1.1893. The Walmart Warrant is exercisable through July 20, 2027. ​ The Walmart Warrant provides for net share settlement that, if elected by the holder, will reduce the number of shares issued upon exercise to reflect net settlement of the exercise price. The Walmart Warrant provides for certain adjustments that may be made to the exercise price and the number of shares of common stock issuable upon exercise due to customary anti-dilution provisions based on future events. The Walmart Warrant is classified as an equity instrument. ​ At both September 30, 2021 and December 31, 2020, 13,094,217 of the Walmart Warrant Shares had vested. The total amount of provision for common stock warrants recorded as a reduction of revenue for the Walmart Warrant during the three months ended September 30, 2021 and 2020 was $1.2 million and $1.3 million, respectively. The amount of provision for common stock warrants recorded as a reduction of revenue for the Walmart Warrant during the nine months ended September 30, 2021 and 2020 was $4.4 million and $3.2 million, respectively. During the three months ended March 31, 2021, the Walmart Warrant had been exercised with respect to 7,274,565 shares of common stock. There were no exercises during the second or third quarter of 2021. ​

Revenue

Revenue	9 Months Ended
	Sep. 30, 2021
Revenue
Revenue	13. Revenue ​ Disaggregation of revenue ​ The following table provides information about disaggregation of revenue (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Major products/services lines ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended September 30, ​ Nine months ended September 30, ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 Sales of fuel cell systems ​ $ 67,032 ​ $ 51,998 ​ $ 152,620 ​ $ 107,515 Sale of hydrogen installations and other infrastructure ​ ​ 48,967 ​ ​ 31,664 ​ ​ 109,429 ​ ​ 44,361 Services performed on fuel cell systems and related infrastructure ​ ​ 6,677 ​ ​ 6,829 ​ ​ 18,397 ​ ​ 19,586 Power Purchase Agreements ​ ​ 9,321 ​ ​ 6,629 ​ ​ 25,508 ​ ​ 19,629 Fuel delivered to customers ​ ​ 11,556 ​ ​ 9,831 ​ ​ 33,804 ​ ​ 24,536 Other ​ ​ 369 ​ ​ 97 ​ ​ 679 ​ ​ 235 Net revenue ​ $ 143,922 ​ $ 107,048 ​ $ 340,437 ​ $ 215,862 ​ Contract balances ​ The following table provides information about receivables, contract assets and contract liabilities from contracts with customers (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 Accounts receivable ​ $ 132,370 ​ $ 43,041 Contract assets ​ ​ 9,284 ​ ​ 18,189 Contract liabilities ​ ​ 115,595 ​ ​ 76,285 ​ Contract assets relate to contracts for which revenue is recognized on a straight-line basis; however, billings escalate over the life of a contract. Contract assets also include amounts recognized as revenue in advance of billings to customers, which are dependent upon the satisfaction of another performance obligation. These amounts are included within prepaid expenses and other current assets on the accompanying unaudited interim condensed consolidated balance sheets. ​ The contract liabilities relate to the advance consideration received from customers for services that will be recognized over time (primarily fuel cell and related infrastructure services) and advance consideration received from customers prior to delivery of products. As of September 30, 2021, the amount of contract liabilities included within deferred revenue was $98.9 million and the amount of contract liabilities within other current liabilities was $16.7 million on the accompanying unaudited interim condensed consolidated balance sheets. As of December 31, 2020, the amount of contract liabilities included within deferred revenue was $56.2 million and the amount of contract liabilities within other current liabilities was $20.1 million. ​ Significant changes in the contract assets and the contract liabilities balances during the period are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Contract assets ​ Nine months ended ​ ​ September 30, 2021 Transferred to receivables from contract assets recognized at the beginning of the period ​ $ (13,344) Revenue recognized and not billed as of the end of the period ​ ​ 4,439 Net change in contract assets ​ ​ (8,905) ​ ​ ​ ​ ​ Contract liabilities ​ Nine months ended ​ ​ September 30, 2021 Increases due to cash received, net of amounts recognized as revenue during the period ​ $ 91,985 Revenue recognized that was included in the contract liability balance as of the beginning of the period ​ ​ (52,675) Net change in contract liabilities ​ $ 39,310 ​ Estimated future revenue ​ Sales of fuel cell systems and hydrogen installations are expected to be recognized as revenue within one year and sales services five ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ ​ 2021 Sales of fuel cell systems ​ $ 23,819 Sale of hydrogen installations and other infrastructure ​ ​ 58,429 Services performed on fuel cell systems and related infrastructure ​ ​ 105,548 Power Purchase Agreements ​ ​ 212,360 Fuel delivered to customers ​ ​ 62,609 Other rental income ​ ​ 2,116 Total estimated future revenue ​ $ 464,881 ​ Contract costs ​ Contract costs consist of capitalized commission fees and other expenses related to obtaining or fulfilling a contract. ​ Capitalized contract costs at September 30, 2021 and December 31, 2020 were $807 thousand and $1.3 million, respectively.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Taxes
Income Taxes	14. Income Taxes ​ The Company did not record any income tax expense or benefit for the three or nine months ended September 30, 2021. The Company recognized an income tax benefit for the three and nine months ended September 30, 2020 of $6.6 and $19.0 Intraperiod Tax Allocation The net deferred tax asset generated from the Company’s net operating loss has been offset by a full valuation allowance because it is more likely than not that the tax benefits of the net operating loss carry forward will not be realized. The Company recognizes accrued interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Measurements
Fair Value Measurements	15. Fair Value Measurements ​ The Company records the fair value of assets and liabilities in accordance with ASC 820, Fair Value Measurement ​ In addition to defining fair value, ASC 820 expands the disclosure requirements around fair value and establishes a fair value hierarchy for valuation inputs. The hierarchy prioritizes the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of the three levels, which is determined by the lowest level input that is significant to the fair value measurement in its entirety. ​ These levels are: ● Level 1 — quoted prices (unadjusted) in active markets for identical assets or liabilities. ● Level 2 — quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. ● Level 3 — unobservable inputs reflecting management’s own assumptions about the inputs used in pricing the asset or liability at fair value. The fair values of the Company’s investments are based upon prices provided by an independent pricing service. Management has assessed and concluded that these prices are reasonable and has not adjusted any prices received from the independent provider. Securities reported at fair value utilizing Level 1 inputs represent assets whose fair value is determined based upon observable unadjusted quoted market prices for identical assets in active markets. Level 2 securities represent assets whose fair value is determined using observable market information such as previous day trade prices, quotes from less active markets or quoted prices of securities with similar characteristics. There were no transfers between Level 1 Level 2 Level the ​ Assets and liabilities measured at fair value on a recurring basis are summarized below (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Carrying ​ Fair ​ Fair Value Measurements ​ ​ Amount ​ Value ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents (1) $ 610,651 $ 610,651 $ 140,574 $ 470,077 $ — Corporate bonds ​ 530,089 ​ 530,089 ​ — ​ 530,089 ​ — Commercial paper ​ 35,795 ​ 35,795 ​ — ​ 35,795 ​ — U.S. Treasuries ​ 169,878 ​ 169,878 ​ 169,878 ​ — ​ — Certificates of deposit ​ 17,004 ​ 17,004 ​ — ​ 17,004 ​ — Equity securities ​ 147,649 ​ 147,649 ​ 147,649 ​ — ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent consideration ​ 18,520 ​ 18,520 ​ — ​ — ​ 18,520 Convertible senior notes ​ 192,320 ​ 1,006,639 ​ — ​ 1,006,639 ​ — Long-term debt ​ 147,255 ​ 147,255 ​ — ​ — ​ 147,255 Finance obligations ​ 207,837 ​ 207,837 ​ — ​ — ​ 207,837 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2020 ​ ​ Carrying ​ Fair ​ Fair Value Measurements ​ ​ Amount ​ Value ​ Level 1 ​ Level 2 ​ Level 3 Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent consideration ​ 9,760 ​ 9,760 ​ — ​ — ​ 9,760 Convertible senior notes ​ 85,640 ​ 1,272,766 ​ — ​ 1,272,766 ​ — Long-term debt ​ 175,402 ​ 175,402 ​ — ​ — ​ 175,402 Finance obligations ​ 181,553 ​ 181,553 ​ — ​ — ​ 181,553 (1) Included in “Cash and cash equivalents” in our unaudited interim condensed consolidated balance sheets as of September 30, 2021. The fair values for available-for-sale and equity securities are based on prices obtained from independent pricing services. Available-for-sale securities are characterized as Level 2 assets, as their fair values are determined using observable market inputs. Equity securities are characterized as Level 1 assets, as their fair values are determined using active markets for identical assets. Financial instruments not recorded at fair value on a recurring basis include equity method investments that have not been remeasured or impaired in the current period, such as our investment in HyVia.

Operating and Finance Lease Lia

Operating and Finance Lease Liabilities	9 Months Ended
	Sep. 30, 2021
Operating and Finance Lease Liabilities
Operating and Finance Lease Liabilities	16. Operating and Finance Lease Liabilities ​ As of September 30, 2021, the Company had operating leases, as lessee, primarily associated with sale/leaseback transactions that are partially secured by restricted cash, security deposits and pledged escrows (see also Note 1, “Nature of Operations”) as summarized below. These leases expire over the next one ​ Leases contain termination clauses with associated penalties, the amount of which cause the likelihood of cancellation to be remote. At the end of the lease term, the leased assets may be returned to the lessor by the Company, the Company may negotiate with the lessor to purchase the assets at fair market value, or the Company may negotiate with the lessor to renew the lease at market rental rates. No residual value guarantees are contained in the leases. No financial covenants are contained within the lease; however there are customary operational covenants such as assurance the Company properly maintains the leased assets and carries appropriate insurance, etc. The leases include credit support in the form of either cash, collateral or letters of credit. See Note 19, “Commitments and Contingencies” for a description of cash held as security associated with the leases. ​ The Company has finance leases associated with its property and equipment in Latham, New York and at fueling customer locations. The fair value of this finance obligation approximated the carrying value as of September 30, 2021. ​ Future minimum lease payments under operating and finance leases (with initial or remaining lease terms in excess of one year) as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Finance ​ Total ​ ​ ​ Operating Lease ​ Lease ​ Lease ​ ​ ​ Liability ​ Liability ​ Liabilities Remainder of 2021 ​ $ 9,929 ​ $ 1,019 ​ $ 10,948 2022 ​ ​ 39,932 ​ 4,012 ​ ​ 43,944 2023 ​ ​ 39,989 ​ 3,989 ​ ​ 43,978 2024 ​ ​ 39,957 ​ 3,996 ​ ​ 43,953 2025 and thereafter ​ ​ 90,241 ​ ​ 10,843 ​ ​ 101,084 Total future minimum payments ​ ​ 220,048 ​ 23,859 ​ ​ 243,907 Less imputed interest ​ ​ (57,364) ​ ​ (4,074) ​ ​ (61,438) Total ​ $ 162,684 ​ $ 19,785 ​ $ 182,469 ​ Rental expense for all operating leases was $9.6 million and $8.1 million for the three months ended September 30, 2021 and 2020, respectively. Rental expense for all operating leases was $25.8 million and $20.6 million for the nine months ended September 30, 2021 and 2020, respectively. ​ The gross profit on sale/leaseback transactions for all operating leases was $30.7 million and $25.2 million for the three months ended September 30, 2021 and 2020, respectively. The gross profit on sale/leaseback transactions for all operating leases was $66.1 million and $44.9 million for the nine months ended September 30, 2021 and 2020, respectively. ​ Right of use assets for sale/leaseback transactions obtained in exchange for new operating lease liabilities was $26.6 million and $24.6 million for the three months ended September 30, 2021 and 2020, respectively. Right of use assets for sale/leaseback transactions obtained in exchange for new operating lease liabilities was $62.5 million and $32.7 million for the nine months ended September 30, 2021 and 2020, respectively. ​ At September 30, 2021 and December 31, 2020, the right of use assets associated with operating leases was $200.2 million and $136.9 million, respectively. The accumulated depreciation for these right of use assets was $32.3 million and $19.9 million at September 30, 2021 and December 31, 2020, respectively. ​ At September 30, 2021 and December 31, 2020, the right of use assets associated with finance leases was $22.8 million and $5.7 million, respectively. The accumulated depreciation for these right of use assets was $757 thousand and $102 thousand at September 30, 2021 and December 31, 2020, respectively. ​ At September 30, 2021 and December 31, 2020, security deposits associated with sale/leaseback transactions were $3.3 million and $5.8 million, respectively, and were included in other assets in the consolidated balance sheets. ​ Other information related to the operating leases are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Nine months ended ​ September 30, 2021 ​ September 30, 2020 Cash payments (in thousands) $ 25,726 ​ $ 14,954 Weighted average remaining lease term (years) ​ 5.72 ​ ​ 4.55 Weighted average discount rate ​ 11.2% ​ ​ 11.8% ​ Right of use assets obtained in exchange for new finance lease liabilities were $5.8 million and $0 for the three months ended September 30, 2021 and 2020, respectively. Right of use assets obtained in exchange for new finance lease liabilities were $17.9 million and $686 thousand for the nine months ended September 30, 2021 and 2020, respectively. ​ Other information related to the finance leases are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Nine months ended ​ September 30, 2021 ​ September 30, 2020 Cash payments (in thousands) $ 2,128 ​ $ 252 Weighted average remaining lease term (years) ​ 4.57 ​ ​ 6.51 Weighted average discount rate ​ 6.9% ​ ​ 9.6% ​

Finance Obligations

Finance Obligations	9 Months Ended
	Sep. 30, 2021
Finance Obligations
Finance Obligations	17. Finance Obligation ​ The Company has sold future services to be performed associated with certain sale/leaseback transactions and recorded the balance as a finance obligation. The outstanding balance of this obligation at September 30, 2021 was $190.5 million, $30.5 million and $160.0 million of which was classified as short-term and long-term, respectively, on the accompanying consolidated balance sheet. The outstanding balance of this obligation at December 31, 2020 was $157.7 million, $24.2 million and $133.5 million of which was classified as short-term and long-term, respectively. The amount is amortized using the effective interest method. The fair value of this finance obligation approximated the carrying value as of September 30, 2021 and December 31, 2020. ​ In prior periods, the Company entered into sale/leaseback transactions that were accounted for as financing transactions and reported as part of finance obligations. The outstanding balance of finance obligations related to sale/leaseback transactions at September 30, 2021 was $17.3 million, $5.1 million and $12.2 million of which was classified as short-term and long-term, respectively on the accompanying consolidated balance sheet. The outstanding balance of this obligation at December 31, 2020 was $23.9 million, $8.0 million and $15.9 million of which was classified as short-term and long-term, respectively on the accompanying consolidated balance sheets. The fair value of this finance obligation approximated the carrying value as of both September 30, 2021 and December 31, 2020. ​ Future minimum payments under finance obligations notes above as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ Sale of Future ​ ​ Sale/leaseback Finance ​ ​ ​ revenue - debt ​ ​ financings Obligations Remainder of 2021 ​ $ 12,788 ​ $ 1,680 ​ $ 14,468 2022 ​ ​ 50,632 ​ ​ 4,975 ​ ​ 55,607 2023 ​ ​ 50,632 ​ ​ 3,148 ​ ​ 53,780 2024 ​ ​ 50,632 ​ ​ 16,154 ​ ​ 66,786 2025 and thereafter ​ ​ 86,614 ​ ​ — ​ ​ 86,614 Total future minimum payments ​ ​ 251,298 ​ ​ 25,957 ​ ​ 277,255 Less imputed interest ​ ​ (60,760) ​ ​ (8,658) ​ ​ (69,418) Total ​ $ 190,538 ​ $ 17,299 ​ $ 207,837 ​ Other information related to the above finance obligations are presented in the following table: ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ ​ Nine months ended ​ ​ September 30, 2021 ​ ​ September 30, 2020 Cash payments (in thousands) $ 41,325 ​ $ 31,693 Weighted average remaining term (years) ​ 4.88 ​ ​ 4.74 Weighted average discount rate ​ 11.3% ​ ​ 11.3% ​

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments
Investments	18. Investments ​ The amortized cost, gross unrealized gains and losses, fair value of those investments classified as available-for-sale, and allowance for credit losses at September 30, 2021 are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Gross ​ Gross ​ Fair ​ Allowance for ​ Cost ​ Unrealized Gains ​ Unrealized Losses ​ Value ​ Credit Losses Corporate bonds $ 533,691 ​ $ 93 ​ $ (3,695) ​ $ 530,089 ​ ​ — Commercial paper ​ 35,719 ​ ​ 76 ​ ​ — ​ ​ 35,795 ​ ​ — Certificates of deposit ​ 17,017 ​ ​ — ​ ​ (13) ​ ​ 17,004 ​ ​ — U.S. Treasuries ​ 170,414 ​ ​ 1 ​ ​ (537) ​ ​ 169,878 ​ ​ — Total $ 756,841 ​ $ 170 ​ $ (4,245) ​ $ 752,766 ​ $ — ​ The cost, gross unrealized gains and losses, and fair value of those investments classified as equity securities at September 30, 2021 are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ ​ ​ Gross ​ Gross ​ Fair ​ ​ Cost ​ Unrealized Gains ​ Unrealized Losses ​ Value Fixed income mutual funds $ 77,766 $ — ​ $ (132) ​ $ 77,634 Exchange traded mutual funds ​ 70,167 ​ ​ — ​ ​ (152) ​ ​ 70,015 Total $ 147,933 ​ $ — ​ $ (284) ​ $ 147,649 ​ A summary of the amortized cost and fair value of investments classified as available-for-sale, by contractual maturity, as of September 30, 2021 is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ Amortized ​ Fair Maturity: ​ Cost ​ Value Within one year $ 447,479 $ 446,011 After one through five years 309,362 ​ 306,755 Total $ 756,841 ​ $ 752,766 ​ Accrued interest income was $4.9 million at September 30, 2021 and is included within the balance for prepaid expenses and other current assets in the unaudited interim condensed consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies
Commitments and Contingencies	19. Commitments and Contingencies ​ Restricted Cash ​ In connection with certain of the above noted sale/leaseback agreements, cash of $301.3 million was required to be restricted as security as of September 30, 2021, which restricted cash will be released over the lease term. As of September 30, 2021, the Company also had certain letters of credit backed by restricted cash totaling $137.7 million that are security for the above noted sale/leaseback agreements. ​ Litigation ​ Legal matters are defended and handled in the ordinary course of business. Liabilities for loss contingencies arising from claims, assessments, litigation, fines, and penalties and other sources are recorded when it is probable that a liability has been incurred and the amount can be reasonably estimated. Legal costs incurred in connection with loss contingencies are expensed as incurred. The Company has not recorded any accruals related to any legal matters. ​ Concentrations of Credit Risk ​ Financial instruments that potentially subject the Company to credit risk consist principally of cash, cash equivalents, restricted cash, accounts receivable and marketable securities. Cash and restricted cash are maintained in accounts with financial institutions, which, at times may exceed the Federal depository insurance coverage of $0.25 million. The Company has not experienced losses on these accounts and management believes, based upon the quality of the financial institutions, that the credit risk with regard to these deposits is not significant. The Company’s available-for-sale securities consists primarily of investments in commercial paper, U.S. Treasury securities, and short-term high credit quality corporate debt securities. Equity securities are comprised of fixed income and equity market index mutual funds. ​ Concentrations of credit risk with respect to receivables exist due to the limited number of select customers with whom the Company has commercial sales arrangements. To mitigate credit risk, the Company performs appropriate evaluation of a prospective customer’s financial condition. ​ At September 30, 2021, one customer comprised 79.6% of the total accounts receivable balance. At December 31, 2020, three customers comprised 73.9% of the total accounts receivable balance. ​ For purposes of assigning a customer to a sale/leaseback transaction completed with a financial institution, the Company considers the end user of the assets to be the ultimate customer. For the three and nine months ended September 30, 2021, 80.1% and 80.6%, of total consolidated revenues were associated with two and three customers, respectively. For the three and nine months ended September 30, 2020, 83.0% and 71.8% of total consolidated revenues were associated primarily with three and two customers, respectively. ​

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2021
Employee Benefit Plans
Employee Benefit Plans	20. Employee Benefit Plans ​ 2011 and 2021 Stock Option and Incentive Plan ​ On May 12, 2011, the Company’s stockholders approved the 2011 Stock Option and Incentive Plan (the “2011 Plan”). The 2011 Plan provided for the issuance of up to a maximum number of shares of common stock equal to the sum of (i) 1,000,000, plus (ii) the number of shares of common stock underlying any grants pursuant to the 2011 Plan or the Plug Power Inc. 1999 Stock Option and Incentive Plan that are forfeited, canceled, repurchased or are terminated (other than by exercise). The shares were issued pursuant to stock options, stock appreciation rights, restricted stock awards and certain other equity-based awards granted to employees, directors and consultants of the Company. No further grants may be made under the 2011 Plan after May 12, 2021. Through various amendments to the 2011 Plan approved by the Company’s stockholders, the number of shares of the Company’s common stock authorized for issuance under the 2011 Plan had been increased to 42.4 million. The Company recorded expenses of approximately $12.7 million and $2.3 million, for the three months ended September 30, 2021 and 2020, respectively, in connection with the 2011 Plan. The Company recorded expense of approximately $32.3 million and $7.3 million, for the nine months ended September 30, 2021 and 2020, respectively, in connection with the 2011 Plan. In July 2021, the 2021 Stock Option Incentive Plan (the “2021 Plan”) was approved by the Company’s stockholders. The 2021 Plan provides for the issuance of up to a maximum number of shares of common stock equal to the sum of (i) 22,500,000 shares, plus 473,491 shares remaining under the 2011 Plan that were rolled into the 2021 Plan, plus (iii) shares underlying any awards under the 2011 Plan that are forfeited, canceled, cash-settled or otherwise terminated, other than by exercise. ​ Option Awards ​ The Company issues options that are time and performance-based awards. All option awards are determined to be classified as equity awards. ​ Service Stock Options Awards ​ To date, options granted under the 2011 and 2021 Plans have vesting provisions ranging from one ​ ​ ​ ​ ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 Expected term of options (years) ​ 3-5 ​ 6 Risk free interest rate ​ 0.61% - 1.05% ​ 0.37% - 1.37% Volatility ​ 72.46% - 75.52% ​ 64.19% - 66.94% ​ There was no expected dividend yield for the service stock options granted. ​ The Company has historically used the simplified method in determining its expected term of all its service stock option grants in all periods presented. The simplified method was used because the Company did not believe historical exercise data provided a reasonable basis for the expected term of its grants, primarily as a result of the limited number of service stock option exercises that have historically occurred. Due to the recent increase in exercise activity at the Company, beginning in the second quarter of 2021, the expected term is based on the Company’s historical experience with employee early exercise behavior. The estimated stock price volatility was derived from the Company’s actual historic stock prices over the past five years, which represents the Company’s best estimate of expected volatility. ​ The following table reflects the service stock option activity for the nine months ended September 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Shares ​ Price ​ Terms ​ Value Options outstanding at December 31, 2020 ​ 10,284,498 ​ $ 5.78 ​ 7.8 ​ $ 289,316 Granted ​ 1,870,835 ​ ​ 32.48 ​ — ​ ​ — Exercised ​ (1,911,112) ​ ​ 2.78 ​ — ​ ​ — Forfeited ​ (15,833) ​ ​ 21.35 ​ — ​ ​ — Expired ​ (4,100) ​ ​ 6.10 ​ — ​ ​ — Options outstanding at September 30, 2021 ​ 10,224,288 ​ $ 11.21 ​ 7.9 ​ $ 146,581 Options exercisable at September 30, 2021 ​ 5,045,168 ​ ​ 4.46 ​ 6.7 ​ ​ 106,360 Options unvested at September 30, 2021 ​ 5,179,120 ​ $ 17.77 ​ 9.0 ​ $ 40,221 ​ The weighted average grant-date fair value of the service stock options granted during the three months ended September 30, 2021 and 2020 was $15.82 and $7.45, respectively. The weighted average grant-date fair value of the service stock options granted during the nine months ended September 30, 2021 and 2020 was $19.76 and $7.21, respectively. The total fair value of the service stock options that vested during the three months ended September 30, 2021 and 2020 was approximately $10.4 million and $5.2 million, respectively. The total fair value of the service stock options that vested during the nine months ended September 30, 2021 and 2020 was approximately $10.9 million and $5.9 million, respectively. ​ Compensation cost associated with service stock options represented approximately $4.2 million and $1.1 million of the total share-based payment expense recorded for the three months ended September 30, 2021 and September 30, 2020, respectively. Compensation cost associated with service stock options represented approximately $11.9 million and 4.1 million of the total share-based payment expense recorded for the nine months ended September 30, 2021 and September 30, 2020, respectively. As of September 30, 2021 and 2020 there was approximately $50.2 million and $8.2 million of unrecognized compensation cost related to service stock option awards to be recognized over the next three years. ​ Performance Stock Option Awards ​ In September 2021, the Compensation Committee approved the grant of performance stock options to the Company’s Chief Executive Officer and certain other executive officers. These performance stock options are subject to both performance-based conditions tied to the achievement of stock price hurdles and time-based vesting; therefore, a Monte Carlo Simulation was utilized to determine the grant date fair value with the associated expense recognized over the requisite service period. Up to one-third (1/3) the performance stock options will vest and become exercisable on each of the first three anniversaries of the grant date, provided that the volume weighted average price of the Company’s common stock during any 30 consecutive trading day period in the three year performance period following the grant date of the stock options (“VWAP”) equals or exceeds certain levels. For the Company’s Chief Executive Officer, 25% of his performance stock options will be deemed to have satisfied the performance-based conditions and will be eligible to be exercised over time if the VWAP equals or exceeds $35; an additional 25% of his options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $50; an additional 16.675% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $65; an additional 16.65% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $80; and the remaining 16.675% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $100. There will be no interpolation for the Chief Executive Officer’s performance stock option if the VWAP falls between any two stock price hurdles, unless in the event of a change in control. For executive officers other than the Chief Executive Officer, 25% of the performance stock options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals $35; an additional 25% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals $50; and the remaining 50% of the options will be deemed to have satisfied the performance-based condition and will be eligible to be exercised if the VWAP equals or exceeds $100. If the VWAP falls between two of the stock price hurdles, an incremental number of options will become exercisable based on linear interpolation in $1 increments. Failure to achieve any of the stock price hurdles applicable to a performance stock option during the three-year performance period will result in the applicable options not becoming exercisable. The performance-based stock options have a maximum term of seven years from the grant date. ​ Key inputs and assumptions used to estimate the fair value of performance stock options include the grant price of the awards, the expected option term, VWAP hurdle rates, volatility of the Company’s stock, an appropriate risk-free rate, and the Company’s dividend yield. Estimates of fair value are not intended to predict actual future events or the value ultimately realized by employees who receive equity awards, and subsequent events are not indicative of the reasonableness of the original estimates of fair value made by the Company. ​ The following table presents key assumptions used to estimate the fair value of the performance stock option awards granted in 2021: ​ ​ ​ ​ ​ ​ ​ September 30, ​ ​ 2021 Remaining VWAP performance period (years) ​ 3 Risk- free interest rate ​ 1.12% Expected volatility ​ 70.00% Closing stock price on grant date ​ $ 26.92 ​ The following table reflects the performance stock option award activity for the nine months ended September 30, 2021. Solely for the purposes of this table, the number of performance options is based on participants earning the maximum number of performance options (i.e 200% of the target number of performance options). ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Shares ​ Price ​ Terms ​ Value Granted ​ 14,560,000 ​ ​ 26.92 ​ — ​ ​ — Options outstanding at September 30, 2021 ​ 14,560,000 ​ $ 26.92 ​ 6.98 ​ $ — Options unvested at September 30, 2021 ​ 14,560,000 ​ $ 26.92 ​ 6.98 ​ $ — ​ The weighted average grant-date fair value of performance stock options granted during the three months and nine months ended September 30, 2021 was $12.78. There were no performance stock options that were exercised during the three months and nine months ended September 30, 2021. ​ Compensation cost associated with performance stock options represented approximately $2.0 million of the total share-based payment expense recorded for the three months and nine months ended September 30, 2021. As of September, 30, 2021, there was approximately $183.7 million of unrecognized compensation cost related to performance stock option awards to be recognized over the next three years. ​ Restricted Stock Awards ​ Restricted stock awards generally vest in equal installments over a period of one ​ A summary of restricted stock activity for the year ended September 30, 2021 is as follows (in thousands except share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Aggregate ​ ​ ​ ​ Intrinsic ​ ​ ​ Shares ​ Value ​ Unvested restricted stock at December 31, 2020 ​ 5,874,642 ​ $ — ​ Granted ​ 1,812,856 ​ ​ — ​ Vested ​ (2,713,789) ​ ​ — ​ Forfeited ​ (13,333) ​ ​ — ​ Unvested restricted stock at September 30, 2021 ​ 4,960,376 ​ $ 126,688 ​ ​ 401(k) Savings & Retirement Plan ​ The Company offers a 401(k) Savings & Retirement Plan to eligible employees meeting certain age and service requirements. This plan permits participants to contribute 100% of their salary, up to the maximum allowable by the Internal Revenue Service regulations. Participants are immediately vested in their voluntary contributions plus actual earnings or less actual losses thereon. Participants are vested in the Company’s matching contribution based on years of service completed. Participants are fully vested upon completion of three years of service. During 2018, the Company began funding its matching contribution in a combination of cash and common stock. The Company issued 54,531 shares of common stock and 368,903 shares of common stock pursuant to the Plug Power Inc. 401(k) Savings & Retirement Plan during the nine months ended September 30, 2021 and 2020, respectively. ​ The Company’s expense for this plan was approximately $1.1 million, and $0.6 million for the three months ended September 30, 2021 and 2020, respectively. The Company’s expense for this plan was approximately $3.4 million, and $1.9 million for the nine months ended September 30, 2021 and 2020, respectively. ​ Non-Employee Director Compensation ​ Each non-employee director is paid an annual retainer for his or her service, in the form of either cash or stock compensation. The Company granted 3,685 shares of common stock and 4,146 shares of common stock to non-employee directors as compensation for the three months ended September 30, 2021 and 2020, respectively. The Company granted 8,923 shares of common stock and 26,636 shares of common stock to non-employee directors as compensation for the nine months ended September 30, 2021 and 2020, respectively. All common stock issued is fully vested at the time of issuance and is valued at fair value on the date of issuance. The Company’s share-based compensation expense in connection with non-employee director compensation was approximately $99 thousand and $56 thousand for the three months ended September 30, 2021 and 2020, respectively. The Company’s share-based compensation expense in connection with non-employee director compensation was approximately $277 thousand and $167 thousand for the nine months ended September 30, 2021 and 2020, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events
Subsequent Events	21. Subsequent Events ​ In November 2021, the Company entered into a signing protocol to acquire Frames Group (“Frames”), a leader in engineering, process and systems integration serving the energy sector. The purchase price is approximately €115 million, of which €30 million is based on future earnouts over the next four years from the completion date. Plug Power will leverage Frames’ capabilities as well as its existing network of suppliers and contract manufacturing facilities to deliver electrolyzer solutions of all sizes, from one megawatt (MW) containerized solutions to solutions for 100 MW-1,000 MW standalone plants or integrated into customers’ processes. The acquisition is expected to be completed by the end of the year, and is subject to customary closing conditions, including receipt of Dutch works council advice. ​ On October 14, 2021, the Company and its wholly-owned subsidiary Plug Power Hydrogen Holdings, Inc. entered into a definitive agreement for the acquisition of Applied Cryo Technologies, Inc. for a purchase price of approximately $170 million, of which $40 million will be in stock and $30 million will be based on future earnouts over the next two and half years. Applied Cryo Technologies, Inc. is a leading provider of technology, equipment and services for the transportation, storage and distribution of liquified hydrogen, oxygen, argon, nitrogen and other cryogenic gases. The acquisition is expected to close during the fourth quarter of 2021 and is subject to customary closing conditions, including receipt of all approvals or the termination or expiration of all waiting periods required under applicable antitrust laws. ​ In October 2021, the Company and SK E&S Co., Ltd., an energy company affiliated with SK Holdings Co., Ltd., formed H2A, which is a joint venture designed to accelerate the use of hydrogen as an alternative energy source in Asian markets.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Restatement	Restatement ​ As previously disclosed in the Explanatory Note to the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020 (the “2020 10-K”), the Company restated its previously issued audited consolidated financial statements as of and for the years ended December 31, 2019 and 2018 and its unaudited interim condensed consolidated financial statements as of and for each of the quarterly periods ended March 31, 2020 and 2019, June 30, 2020 and 2019, September 30, 2020 and 2019 and December 31, 2019. ​ Previously filed annual reports on Form 10-K and quarterly reports on Form 10-Q for the periods affected by the restatement have not been amended. Accordingly, investors should not rely upon the Company’s previously released financial statements for these periods and any earnings releases or other communications relating to these periods, and, for these periods, investors should rely solely on the financial statements and other financial data for the relevant periods included in the 2020 10-K. Commencing with our quarterly report on Form 10-Q for the quarterly period ended March 31, 2021, we are including in our quarterly reports for fiscal 2021 restated results for the corresponding interim periods of fiscal 2020.
Principles of Consolidation	Principles of Consolidation ​ The unaudited interim condensed consolidated financial statements include the financial statements of the Company and its wholly-owned subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. In addition, we include our share of the results of HyVia using the equity method based on our economic ownership interest and our ability to exercise significant influence over the operating and financial decisions of HyVia. ​
Interim Financial Statements	Interim Financial Statements ​ The accompanying unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). In the opinion of management, all adjustments, which consist solely of normal recurring adjustments, necessary to present fairly, in accordance with U.S. generally accepted accounting principles (“GAAP”), the financial position, results of operations and cash flows for all periods presented, have been made. The results of operations for the interim periods presented are not necessarily indicative of the results that may be expected for the full year. ​ Certain information and footnote disclosures normally included in annual consolidated financial statements prepared in accordance with GAAP have been condensed or omitted. These unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto included in the Company’s 2020 10-K. ​ The information presented in the accompanying unaudited interim condensed consolidated balance sheets as of December 31, 2020 has been derived from the Company’s December 31, 2020 audited consolidated financial statements. ​ Certain amounts in the prior period condensed consolidated financial statements have been reclassified to conform to the presentation of the current period condensed consolidated financial statements. ​ ​ There have been no changes in our accounting policies from those reported in our 2020 10-K, except for the adoption of 2020-06, as described in the Recently Adopted Accounting Guidance section. We have also expanded our accounting policy relating to cash equivalents, available-for-sale securities, equity securities, and stock-based compensation as follows: ​
Cash Equivalents	Cash Equivalents ​ The Company considers all highly-liquid debt securities with original maturities of three months or less to be cash equivalents. At September 30, 2021, cash equivalents consisted of commercial paper and U.S. Treasury securities with original maturities of three months or less, and money market funds. Due to their short-term nature, the carrying amounts reported in the unaudited interim condensed consolidated balance sheets approximate the fair value of cash and cash equivalents.
Available-for-sale securities	Available-for-sale securities ​ Available-for-sale securities is comprised of commercial paper with original maturities greater than three months, U.S. Treasury securities, certificates of deposit and corporate bonds. We consider these securities to be ​ Available-for-sale securities are recorded at fair value as of each balance sheet date. As of each balance sheet date, unrealized gains and losses, with the exception of credit related losses, are recorded to accumulated other comprehensive income (loss). Any credit related losses are recognized as a credit loss allowance on the balance sheet with a corresponding adjustment to operations. Realized gains and losses are due to the sale and maturity of securities classified as available-for-sale and represent the net gain (loss) from accumulated other comprehensive income (loss) reclassifications for previously unrealized net gains on available-for-sale debt securities. ​
Equity securities	Equity securities ​ Equity securities are comprised of fixed income and equity market index mutual funds. Equity securities are valued at fair value with changes in the fair value recognized in our unaudited interim condensed consolidated statement of operations. We consider these securities to be
Stock-Based Compensation	Stock-based compensation Stock-based compensation represents the cost related to stock-based awards granted to employees and directors. The Company measures stock-based compensation cost at grant date, based on the fair value of the award estimated under the current provisions of Accounting Standards Codification (“ASC”) Topic 718, Compensation - Stock Compensation. For service stock options and restricted stock awards, the Company estimates the fair value of stock-based awards using a Black-Scholes valuation model and recognizes the cost as expense on a straight-line basis over the option’s requisite service period. In September 2021, the Company also issued performance stock option awards that include a market condition. The grant date fair value of performance stock options is estimated using a Monte Carlo simulation model and the cost is recognized using the accelerated attribution method. Stock-based compensation expense is recorded in cost of revenue associated with sales of fuel cell systems and related infrastructure, cost of revenue for services performed on fuel cell systems and related infrastructure, research and development expense and selling, general and administrative expenses in the consolidated statements of operations based on the employees’ respective function.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Guidance ​ Other than the adoption of the accounting guidance mentioned i n our 2020 10-K and ASU 2020-06 On January 1, 2021, we early adopted ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) using the modified retrospective approach. Consequently, the Company’s 3.75% Convertible Senior Notes due 2025 (the “3.75% Convertible Senior Notes”) is now accounted for as a single liability measured at its amortized cost. This accounting change removed the impact of recognizing the equity component of the Company’s convertible notes at issuance and the subsequent accounting impact of additional interest expense from debt discount amortization. Future interest expense of the convertible notes will be lower as a result of adoption of this guidance and net loss per share will be computed using the if-converted method for convertible instruments. The cumulative effect of the accounting change upon adoption on January 1, 2021 increased the carrying amount of the 3.75% Convertible Senior Notes by $120.6 million, reduced accumulated deficit by $9.6 million and reduced additional paid-in capital by $130.2 million as of September 30, 2021. Recent Accounting Guidance Not Yet Effective ​ All issued but not yet effective accounting and reporting standards as of September 30, 2021 are either not applicable to the Company or are not expected to have a material impact on the Company.

Extended Maintenance Contracts

Extended Maintenance Contracts (Tables)	9 Months Ended
	Sep. 30, 2021
Extended Maintenance Contracts
Schedule of accrual for loss contracts	The following table shows the rollforward of balance in the accrual for loss contracts, including changes due to the passage of time, additions, and changes in estimates (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Year ended ​ September 30, 2021 ​ December 31, 2020 Beginning Balance $ 24,013 ​ $ 3,702 Provision for Loss Accrual ​ 15,641 ​ ​ 35,473 Released to Service Cost of Sales ​ (6,055) ​ ​ (2,348) Released to Provision for Warrants ​ — ​ ​ (12,814) Ending Balance $ 33,599 ​ $ 24,013

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share
Schedule of potential dilutive common shares	​ ​ ​ ​ ​ ​ ​ ​ At September 30, ​ 2021 2020 Stock options outstanding (1) ​ 24,784,288 14,434,983 Restricted stock outstanding (2) ​ 4,960,376 5,992,974 Common stock warrants (3) ​ 80,017,181 ​ 110,573,392 Convertible Senior Notes (4) ​ 39,170,766 56,872,730 Number of dilutive potential shares of common stock ​ 148,932,611 187,874,079 ​ (1) During the three months ended September 30, 2021 and 2020, the Company granted 15,732,335 and 3,192,400 stock options, respectively. During the nine months ended September 30, 2021 and 2020, the Company granted 16,430,835 and 3,367,049 stock options, respectively. ​ (2) During the three months ended September 30, 2021 and 2020, the Company granted 1,159,856 and 3,095,000 shares of restricted stock, respectively. During the nine months ended September 30, 2021 and 2020, the Company granted 1,812,856 and 3,189,649 shares of restricted stock, respectively. ​ (3) In April 2017, the Company issued a warrant to acquire up to 55,286,696 shares of the Company’s common stock as part of a transaction agreement with Amazon, subject to certain vesting events, as described in Note 12, “Warrant Transaction Agreements.” The warrant had been exercised with respect to 17,461,994 shares of the Company’s common stock as of September 30, 2021. ​ In July 2017, the Company issued a warrant to acquire up to 55,286,696 shares of the Company’s common stock as part of a transaction agreement with Walmart, subject to certain vesting events, as described in Note 12, “Warrant Transaction Agreements.” The warrant had been exercised with respect to 13,094,217 shares of the Company’s common stock as of September 30, 2021. ​ (4) In March 2018, the Company issued $100.0 million in aggregate principal amount of the 5.5% Convertible Senior Notes due 2023 (the “5.5% Convertible Senior Notes”). In May 2020, the Company repurchased $66.3 million of the 5.5% Convertible Senior Notes and in the fourth quarter of 2020, $33.5 million of the 5.5% Convertible Senior Notes were converted into approximately 14.6 million shares of common stock. The remaining $160 thousand aggregate principal amount of the 5.5% Convertible Senior Notes were converted into 69,808 shares of common stock in January 2021. In September 2019, the Company issued $40.0 million in aggregate principal amount of the 7.5% Convertible Senior Note due 2023 (the “7.5% Convertible Senior Note”), which was fully converted into 16.0 million shares of common stock on July 1, 2020. In May 2020, the Company issued $212.5 million in aggregate principal amount of the 3.75% Convertible Senior Notes. During the first quarter of 2021, $15.2 million of the 3.75% Convertible Senior Notes were converted into 3,016,036 shares of common stock. There were no conversions in the second or third quarter of 2021.

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2021
Inventory
Schedule of Inventory	Inventory as of September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 ​ 2020 ​ Raw materials and supplies - production locations ​ $ 147,085 ​ $ 92,221 ​ Raw materials and supplies - customer locations ​ ​ 13,611 ​ ​ 12,405 ​ Work-in-process ​ 61,525 ​ 29,349 ​ Finished goods ​ 7,593 ​ 5,411 ​ Inventory ​ $ 229,814 ​ $ 139,386 ​

Equipment Related to Power Pu_2

Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net (Tables)	9 Months Ended
	Sep. 30, 2021
Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net
Schedule of equipment related to power purchase agreements and fuel delivered to customers, net	Equipment related to power purchase agreements and fuel delivered to customers, net at September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 ​ 2020 Equipment related to power purchase agreements and fuel delivered to customers ​ $ 99,230 ​ $ 92,736 ​ Less: accumulated depreciation ​ ​ (20,519) ​ ​ (16,929) ​ Equipment related to power purchase agreements and fuel delivered to customers, net ​ ​ 78,711 ​ ​ 75,807 ​

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment
Schedule of Property plant and equipment	Property, plant and equipment at September 30, 2021 and December 31, 2020 consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ December 31, 2020 Land ​ ​ 1,165 ​ ​ 1,165 Leasehold improvements ​ $ 1,440 ​ $ 1,121 Construction in progress ​ ​ 100,136 ​ ​ 15,590 Software, machinery, and equipment ​ 94,200 ​ 78,859 Property, plant, and equipment ​ 196,941 ​ 96,735 Less: accumulated depreciation ​ (27,355) ​ (22,186) Property, plant, and equipment, net ​ $ 169,586 ​ $ 74,549

Intangible Assets and Goodwill

Intangible Assets and Goodwill (Tables)	9 Months Ended
	Sep. 30, 2021
Intangible Assets and Goodwill
Schedule of Intangible assets	The gross carrying amount and accumulated amortization of the Company’s acquired identifiable intangible assets as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ Gross Carrying ​ Accumulated ​ ​ ​ ​ ​ ​ Amortization Period ​ Amount ​ Amortization ​ Total Acquired technology 10 years $ 13,040 ​ $ (4,888) ​ $ 8,152 ​ Customer relationships, Non-compete agreements, Backlog & Trademark ​ 6 years ​ 890 ​ ​ (398) ​ ​ 492 ​ In process research and development Indefinite ​ ​ 29,000 ​ ​ — ​ ​ 29,000 ​ ​ ​ ​ ​ $ 42,930 ​ $ (5,286) ​ $ 37,644 ​ ​ The gross carrying amount and accumulated amortization of the Company’s acquired identifiable intangible assets as of December 31, 2020 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ Gross Carrying ​ Accumulated ​ ​ ​ ​ ​ ​ Amortization Period ​ Amount ​ Amortization ​ Total Acquired technology 10 years ​ $ 13,697 ​ $ (4,042) ​ $ 9,655 ​ Customer relationships, Non-compete agreements, Backlog & Trademark ​ 6 years ​ ​ 890 ​ ​ (294) ​ ​ 596 ​ In process research and development Indefinite ​ 29,000 ​ ​ — ​ 29,000 ​ ​ ​ ​ ​ $ 43,587 ​ $ (4,336) ​ $ 39,251 ​
Schedule of future amortization of intangible assets	The estimated amortization expense for subsequent years is as follows (in thousands): ​ ​ ​ ​ ​ Remainder of 2021 $ 363 2022 ​ ​ 1,453 2023 ​ ​ 1,453 2024 ​ ​ 1,431 2025 and thereafter ​ ​ 3,944 Total ​ $ 8,644

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Long-Term Debt
Summary of principal payments of long term debt	As of September 30, 2021, the Term Loan Facility requires the principal balance as of each of the following dates not to exceed the following (in thousands): ​ ​ ​ ​ December 31, 2021 $ 127,317 December 31, 2022 ​ 93,321 December 31, 2023 ​ 62,920 December 31, 2024 ​ 33,692 December 31, 2025 ​ —

Convertible Senior Notes (Table

Convertible Senior Notes (Tables) - 3.75% Convertible Senior Notes	9 Months Ended
	Sep. 30, 2021
Debt Instrument [Line Items]
Schedule of net proceeds from the Convertible Senior Notes	​ ​ ​ ​ ​ Amount ​ (in thousands) Principal amount $ 212,463 Less initial purchasers' discount ​ (6,374) Less cost of related capped calls ​ (16,253) Less other issuance costs ​ (617) Net proceeds $ 189,219
Schedule of Convertible Senior Notes	The 3.75% Convertible Senior Notes consisted of the following (in thousands): ​ ​ ​ ​ ​ September 30, ​ 2021 Principal amounts: ​ ​ Principal $ 197,278 Unamortized debt issuance costs (1) ​ (4,958) Net carrying amount $ 192,320 1) Included in the unaudited interim condensed consolidated balance sheets within the 3.75% Convertible Senior Notes, net and amortized over the remaining life of the notes using the effective interest rate method. ​
Schedule of debt	The following table summarizes the total interest expense and effective interest rate related to the 3.75% Convertible Senior Notes (in thousands, except for effective interest rate): ​ ​ ​ ​ ​ ​ September 30, ​ 2021 Interest expense $ 1,849 Amortization of debt issuance costs ​ 306 Total ​ 2,155 ​ ​ ​ Effective interest rate ​ 4.50% ​

Warrant Transaction Agreements

Warrant Transaction Agreements (Tables)	9 Months Ended
	Sep. 30, 2021
Warrant Transaction Agreements
Schedule of warranty assumptions	​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ November 2, 2020 Risk-free interest rate ​ 0.58% ​ 0.58% Volatility ​ 75.00% ​ 75.00% Expected average term ​ 6.26 ​ 6.42 Exercise price ​ $13.81 ​ $13.81 Stock price ​ $33.91 ​ $15.47

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue
Schedule of disaggregation of revenue	The following table provides information about disaggregation of revenue (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Major products/services lines ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three months ended September 30, ​ Nine months ended September 30, ​ ​ 2021 ​ 2020 ​ 2021 ​ 2020 Sales of fuel cell systems ​ $ 67,032 ​ $ 51,998 ​ $ 152,620 ​ $ 107,515 Sale of hydrogen installations and other infrastructure ​ ​ 48,967 ​ ​ 31,664 ​ ​ 109,429 ​ ​ 44,361 Services performed on fuel cell systems and related infrastructure ​ ​ 6,677 ​ ​ 6,829 ​ ​ 18,397 ​ ​ 19,586 Power Purchase Agreements ​ ​ 9,321 ​ ​ 6,629 ​ ​ 25,508 ​ ​ 19,629 Fuel delivered to customers ​ ​ 11,556 ​ ​ 9,831 ​ ​ 33,804 ​ ​ 24,536 Other ​ ​ 369 ​ ​ 97 ​ ​ 679 ​ ​ 235 Net revenue ​ $ 143,922 ​ $ 107,048 ​ $ 340,437 ​ $ 215,862 ​
Schedule of receivables, contract assets and contract liabilities from contracts with customers	The following table provides information about receivables, contract assets and contract liabilities from contracts with customers (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 ​ 2020 Accounts receivable ​ $ 132,370 ​ $ 43,041 Contract assets ​ ​ 9,284 ​ ​ 18,189 Contract liabilities ​ ​ 115,595 ​ ​ 76,285
Schedule of changes in contract assets and the contract liabilities	Significant changes in the contract assets and the contract liabilities balances during the period are as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Contract assets ​ Nine months ended ​ ​ September 30, 2021 Transferred to receivables from contract assets recognized at the beginning of the period ​ $ (13,344) Revenue recognized and not billed as of the end of the period ​ ​ 4,439 Net change in contract assets ​ ​ (8,905) ​ ​ ​ ​ ​ Contract liabilities ​ Nine months ended ​ ​ September 30, 2021 Increases due to cash received, net of amounts recognized as revenue during the period ​ $ 91,985 Revenue recognized that was included in the contract liability balance as of the beginning of the period ​ ​ (52,675) Net change in contract liabilities ​ $ 39,310
Schedule of Estimated future revenue	Sales of fuel cell systems and hydrogen installations are expected to be recognized as revenue within one year and sales services five ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ ​ 2021 Sales of fuel cell systems ​ $ 23,819 Sale of hydrogen installations and other infrastructure ​ ​ 58,429 Services performed on fuel cell systems and related infrastructure ​ ​ 105,548 Power Purchase Agreements ​ ​ 212,360 Fuel delivered to customers ​ ​ 62,609 Other rental income ​ ​ 2,116 Total estimated future revenue ​ $ 464,881

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Measurements
Schedule of assets and liabilities measured at fair value on a recurring basis	Assets and liabilities measured at fair value on a recurring basis are summarized below (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Carrying ​ Fair ​ Fair Value Measurements ​ ​ Amount ​ Value ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents (1) $ 610,651 $ 610,651 $ 140,574 $ 470,077 $ — Corporate bonds ​ 530,089 ​ 530,089 ​ — ​ 530,089 ​ — Commercial paper ​ 35,795 ​ 35,795 ​ — ​ 35,795 ​ — U.S. Treasuries ​ 169,878 ​ 169,878 ​ 169,878 ​ — ​ — Certificates of deposit ​ 17,004 ​ 17,004 ​ — ​ 17,004 ​ — Equity securities ​ 147,649 ​ 147,649 ​ 147,649 ​ — ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent consideration ​ 18,520 ​ 18,520 ​ — ​ — ​ 18,520 Convertible senior notes ​ 192,320 ​ 1,006,639 ​ — ​ 1,006,639 ​ — Long-term debt ​ 147,255 ​ 147,255 ​ — ​ — ​ 147,255 Finance obligations ​ 207,837 ​ 207,837 ​ — ​ — ​ 207,837 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2020 ​ ​ Carrying ​ Fair ​ Fair Value Measurements ​ ​ Amount ​ Value ​ Level 1 ​ Level 2 ​ Level 3 Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Contingent consideration ​ 9,760 ​ 9,760 ​ — ​ — ​ 9,760 Convertible senior notes ​ 85,640 ​ 1,272,766 ​ — ​ 1,272,766 ​ — Long-term debt ​ 175,402 ​ 175,402 ​ — ​ — ​ 175,402 Finance obligations ​ 181,553 ​ 181,553 ​ — ​ — ​ 181,553 (1) Included in “Cash and cash equivalents” in our unaudited interim condensed consolidated balance sheets as of September 30, 2021.

Operating and Finance Lease L_2

Operating and Finance Lease Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Operating and Finance Lease Liabilities
Schedule of future minimum lease payments under operating leases	Future minimum lease payments under operating and finance leases (with initial or remaining lease terms in excess of one year) as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Finance ​ Total ​ ​ ​ Operating Lease ​ Lease ​ Lease ​ ​ ​ Liability ​ Liability ​ Liabilities Remainder of 2021 ​ $ 9,929 ​ $ 1,019 ​ $ 10,948 2022 ​ ​ 39,932 ​ 4,012 ​ ​ 43,944 2023 ​ ​ 39,989 ​ 3,989 ​ ​ 43,978 2024 ​ ​ 39,957 ​ 3,996 ​ ​ 43,953 2025 and thereafter ​ ​ 90,241 ​ ​ 10,843 ​ ​ 101,084 Total future minimum payments ​ ​ 220,048 ​ 23,859 ​ ​ 243,907 Less imputed interest ​ ​ (57,364) ​ ​ (4,074) ​ ​ (61,438) Total ​ $ 162,684 ​ $ 19,785 ​ $ 182,469
Schedule of operating leases other information	​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Nine months ended ​ September 30, 2021 ​ September 30, 2020 Cash payments (in thousands) $ 25,726 ​ $ 14,954 Weighted average remaining lease term (years) ​ 5.72 ​ ​ 4.55 Weighted average discount rate ​ 11.2% ​ ​ 11.8%
Schedule of finance leases other information	​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Nine months ended ​ September 30, 2021 ​ September 30, 2020 Cash payments (in thousands) $ 2,128 ​ $ 252 Weighted average remaining lease term (years) ​ 4.57 ​ ​ 6.51 Weighted average discount rate ​ 6.9% ​ ​ 9.6%

Finance Obligations (Tables)

Finance Obligations (Tables)	9 Months Ended
	Sep. 30, 2021
Sale Leaseback Transaction [Line Items]
Schedule of finance leases other information	​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ Nine months ended ​ September 30, 2021 ​ September 30, 2020 Cash payments (in thousands) $ 2,128 ​ $ 252 Weighted average remaining lease term (years) ​ 4.57 ​ ​ 6.51 Weighted average discount rate ​ 6.9% ​ ​ 9.6%
Finance obligation
Sale Leaseback Transaction [Line Items]
Schedule of future minimum lease payments under finance obligations	Future minimum payments under finance obligations notes above as of September 30, 2021 were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ Sale of Future ​ ​ Sale/leaseback Finance ​ ​ ​ revenue - debt ​ ​ financings Obligations Remainder of 2021 ​ $ 12,788 ​ $ 1,680 ​ $ 14,468 2022 ​ ​ 50,632 ​ ​ 4,975 ​ ​ 55,607 2023 ​ ​ 50,632 ​ ​ 3,148 ​ ​ 53,780 2024 ​ ​ 50,632 ​ ​ 16,154 ​ ​ 66,786 2025 and thereafter ​ ​ 86,614 ​ ​ — ​ ​ 86,614 Total future minimum payments ​ ​ 251,298 ​ ​ 25,957 ​ ​ 277,255 Less imputed interest ​ ​ (60,760) ​ ​ (8,658) ​ ​ (69,418) Total ​ $ 190,538 ​ $ 17,299 ​ $ 207,837
Schedule of finance leases other information	​ ​ ​ ​ ​ ​ ​ ​ ​ Nine months ended ​ ​ Nine months ended ​ ​ September 30, 2021 ​ ​ September 30, 2020 Cash payments (in thousands) $ 41,325 ​ $ 31,693 Weighted average remaining term (years) ​ 4.88 ​ ​ 4.74 Weighted average discount rate ​ 11.3% ​ ​ 11.3%

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Investments
Schedule of gross unrealized gains and losses, and the amortized cost, allowance for credit losses, and fair value of those investments classified as available-for-sale	The amortized cost, gross unrealized gains and losses, fair value of those investments classified as available-for-sale, and allowance for credit losses at September 30, 2021 are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Gross ​ Gross ​ Fair ​ Allowance for ​ Cost ​ Unrealized Gains ​ Unrealized Losses ​ Value ​ Credit Losses Corporate bonds $ 533,691 ​ $ 93 ​ $ (3,695) ​ $ 530,089 ​ ​ — Commercial paper ​ 35,719 ​ ​ 76 ​ ​ — ​ ​ 35,795 ​ ​ — Certificates of deposit ​ 17,017 ​ ​ — ​ ​ (13) ​ ​ 17,004 ​ ​ — U.S. Treasuries ​ 170,414 ​ ​ 1 ​ ​ (537) ​ ​ 169,878 ​ ​ — Total $ 756,841 ​ $ 170 ​ $ (4,245) ​ $ 752,766 ​ $ —
Schedule of investments classified as equity securities	The cost, gross unrealized gains and losses, and fair value of those investments classified as equity securities at September 30, 2021 are summarized as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ ​ ​ Gross ​ Gross ​ Fair ​ ​ Cost ​ Unrealized Gains ​ Unrealized Losses ​ Value Fixed income mutual funds $ 77,766 $ — ​ $ (132) ​ $ 77,634 Exchange traded mutual funds ​ 70,167 ​ ​ — ​ ​ (152) ​ ​ 70,015 Total $ 147,933 ​ $ — ​ $ (284) ​ $ 147,649
Schedule of the amortized cost and fair value of investments classified as available-for-sale, by contractual maturity	A summary of the amortized cost and fair value of investments classified as available-for-sale, by contractual maturity, as of September 30, 2021 is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ Amortized ​ Fair Maturity: ​ Cost ​ Value Within one year $ 447,479 $ 446,011 After one through five years 309,362 ​ 306,755 Total $ 756,841 ​ $ 752,766

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Nonvested Restricted Stock Shares Activity	A summary of restricted stock activity for the year ended September 30, 2021 is as follows (in thousands except share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Aggregate ​ ​ ​ ​ Intrinsic ​ ​ ​ Shares ​ Value ​ Unvested restricted stock at December 31, 2020 ​ 5,874,642 ​ $ — ​ Granted ​ 1,812,856 ​ ​ — ​ Vested ​ (2,713,789) ​ ​ — ​ Forfeited ​ (13,333) ​ ​ — ​ Unvested restricted stock at September 30, 2021 ​ 4,960,376 ​ $ 126,688 ​
Service Options Awards
Assumptions made for the purpose of estimating fair value	​ ​ ​ ​ ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 Expected term of options (years) ​ 3-5 ​ 6 Risk free interest rate ​ 0.61% - 1.05% ​ 0.37% - 1.37% Volatility ​ 72.46% - 75.52% ​ 64.19% - 66.94%
Schedule of Share-based Compensation, Stock Options, Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Shares ​ Price ​ Terms ​ Value Options outstanding at December 31, 2020 ​ 10,284,498 ​ $ 5.78 ​ 7.8 ​ $ 289,316 Granted ​ 1,870,835 ​ ​ 32.48 ​ — ​ ​ — Exercised ​ (1,911,112) ​ ​ 2.78 ​ — ​ ​ — Forfeited ​ (15,833) ​ ​ 21.35 ​ — ​ ​ — Expired ​ (4,100) ​ ​ 6.10 ​ — ​ ​ — Options outstanding at September 30, 2021 ​ 10,224,288 ​ $ 11.21 ​ 7.9 ​ $ 146,581 Options exercisable at September 30, 2021 ​ 5,045,168 ​ ​ 4.46 ​ 6.7 ​ ​ 106,360 Options unvested at September 30, 2021 ​ 5,179,120 ​ $ 17.77 ​ 9.0 ​ $ 40,221
Performance Option Awards
Assumptions made for the purpose of estimating fair value	​ ​ ​ ​ ​ September 30, ​ ​ 2021 Remaining VWAP performance period (years) ​ 3 Risk- free interest rate ​ 1.12% Expected volatility ​ 70.00% Closing stock price on grant date ​ $ 26.92
Schedule of Share-based Compensation, Stock Options, Activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ ​ Weighted ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ ​ ​ Exercise ​ Contractual ​ Intrinsic ​ ​ Shares ​ Price ​ Terms ​ Value Granted ​ 14,560,000 ​ ​ 26.92 ​ — ​ ​ — Options outstanding at September 30, 2021 ​ 14,560,000 ​ $ 26.92 ​ 6.98 ​ $ — Options unvested at September 30, 2021 ​ 14,560,000 ​ $ 26.92 ​ 6.98 ​ $ —

Nature of Operations - Descript

Nature of Operations - Description Of Business (Details) - HyVia	Sep. 30, 2021
Plug Power France
Description of Business
Ownership interest percentage	50.00%
Renault
Description of Business
Ownership interest percentage	50.00%

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jan. 01, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Convertible Debt		$ 120,600
Accumulated deficit	$ (2,203,989)	9,600	$ (1,946,488)
Additional paid-in capital	$ 6,978,454	$ 130,200	$ 3,446,650
Interest rate (as a percent)		3.75%

Extended Maintenance Contract_2

Extended Maintenance Contracts (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accrual for loss contracts
Beginning Balance	$ 24,013	$ 3,702
Provision for Loss Accrual	15,641	35,473
Released to Service Cost of Sales	(6,055)	(2,348)
Released to Provision for Warrants		(12,814)
Ending Balance	$ 33,599	$ 24,013

Earnings Per Share - Dilutive P

Earnings Per Share - Dilutive Potential Common Shares (Details) - USD ($)	Jan. 07, 2021	Jan. 31, 2021	Sep. 30, 2019	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jan. 01, 2021	May 31, 2020	May 29, 2020	May 18, 2020	Mar. 31, 2018	Jul. 20, 2017	Apr. 04, 2017
Earnings Per Share
Number of dilutive potential common stock									148,932,611	187,874,079
Number of warrants exercised (in shares)				3,501,640					24,736,559
Interest rate (as a percent)											3.75%
3.75% Convertible Senior Notes
Earnings Per Share
Principal amount				$ 197,278,000		$ 15,200,000			$ 197,278,000			$ 212,463,000	$ 12,500,000	$ 200,000,000
Conversion of notes through common stock issuance				0	0	3,016,036			3,000,000
Interest rate (as a percent)				3.75%					3.75%			3.75%	3.75%	3.75%
7.5% Convertible Senior Note
Earnings Per Share
Interest rate (as a percent)			7.50%					7.50%		7.50%
5.5% Convertible Senior Notes
Earnings Per Share
Principal amount	$ 160,000	$ 160,000	$ 40,000,000				$ 33,500,000							$ 100,000,000	$ 100,000,000
Conversion of notes through common stock issuance	69,808	69,808	16,000,000				14,600,000
Conversion of Stock, Shares Issued							14,600,000
Repurchase amount							$ 33,500,000					$ 66,300,000
Interest rate (as a percent)	5.50%	5.50%	7.50%	5.50%			5.50%	5.50%	5.50%	5.50%		5.50%		5.50%	5.50%
Warrant Transaction Agreements
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)																	55,286,696
Number of warrants exercised (in shares)				3,501,640					17,461,994
Warrants issued with the Walmart Stores, Inc transaction agreement
Earnings Per Share
Shares of common stock that can be purchased from warrants issued (in shares)																55,286,696
Number of warrants exercised (in shares)				0	0	7,274,565	5,819,652		13,094,217
Stock options outstanding
Earnings Per Share
Number of dilutive potential common stock									24,784,288	14,434,983
Options granted				15,732,335				3,192,400	16,430,835	3,367,049
Restricted stock outstanding
Earnings Per Share
Number of dilutive potential common stock									4,960,376	5,992,974
Options granted									1,812,856
Common stock warrants
Earnings Per Share
Number of dilutive potential common stock									80,017,181	110,573,392
Convertible senior notes
Earnings Per Share
Number of dilutive potential common stock									39,170,766	56,872,730

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Inventory
Raw materials and supplies - production locations	$ 147,085	$ 92,221
Raw materials and supplies - customer locations	13,611	12,405
Work-in-process	61,525	29,349
Finished goods	7,593	5,411
Inventory	$ 229,814	$ 139,386

Equipment Related to Power Pu_3

Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net - Components (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net
Equipment related to power purchase agreements and fuel delivered to customers	$ 99,230	$ 92,736
Less: accumulated depreciation	(20,519)	(16,929)
Equipment related to power purchase agreements and fuel delivered to customers, net	$ 78,711	$ 75,807

Equipment Related to Power Pu_4

Equipment Related to Power Purchase Agreements and Fuel Delivered to Customers, net (Details) - USD ($)	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Lessor, Lease, Description [Line Items]
Depreciation expense	$ 1,900,000	$ 2,300,000		$ 5,700,000	$ 6,600,000
Fuel tanks purchased	$ 0
Cost Of Revenue, Fuel Delivered To Customers
Lessor, Lease, Description [Line Items]
Termination costs			$ 16,000,000
Minimum
Lessor, Lease, Description [Line Items]
Lease term	1 year			1 year
Maximum
Lessor, Lease, Description [Line Items]
Lease term	10 years			10 years

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, plant and equipment
Property, plant, and equipment, gross	$ 196,941		$ 196,941		$ 96,735
Less: accumulated depreciation	(27,355)		(27,355)		(22,186)
Property, plant, and equipment, net	169,586		169,586		74,549
Capitalized interest			2,600	$ 0
Depreciation expense	1,900	$ 1,400	5,200	$ 3,200
Land
Property, plant and equipment
Property, plant, and equipment, gross	1,165		1,165		1,165
Leasehold Improvements
Property, plant and equipment
Property, plant, and equipment, gross	1,440		1,440		1,121
Construction in progress
Property, plant and equipment
Property, plant, and equipment, gross	100,136		100,136		15,590
Software, machinery and equipment
Property, plant and equipment
Property, plant, and equipment, gross	$ 94,200		$ 94,200		$ 78,859

Intangible Assets and Goodwil_2

Intangible Assets and Goodwill - Gross Carrying Amount (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	$ 42,930	$ 43,587
Accumulated Amortization	(5,286)	(4,336)
Total	37,644	39,251
Goodwill	71,856	72,387
Translation loss on goodwill	(531)
Goodwill impairments	0	0
In process R&D
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	29,000	29,000
Total	$ 29,000	$ 29,000
Acquired technology
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	10 years	10 years
Gross Carrying Amount	$ 13,040	$ 13,697
Accumulated Amortization	(4,888)	(4,042)
Total	$ 8,152	$ 9,655
Customer relationships, Backlog & Trademark
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	6 years	6 years
Gross Carrying Amount	$ 890	$ 890
Accumulated Amortization	(398)	(294)
Total	$ 492	$ 596

Intangible Assets and Goodwil_3

Intangible Assets and Goodwill - Estimated Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Intangible Assets and Goodwill
Amortization of Intangible Assets	$ 400	$ 300	$ 1,095	$ 835
Estimated amortization expense
Remainder of 2021	363		363
2022	1,453		1,453
2023	1,453		1,453
2024	1,431		1,431
2025 and thereafter	3,944		3,944
Total	$ 8,644		$ 8,644

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2021	Dec. 31, 2019	Mar. 31, 2019
Long-Term Debt
Interest rate (as a percent)			3.75%
Percent of securities in foreign subsidiaries guaranteed to secure debt	65.00%
Principal payments of long term debt
December 31, 2021	$ 127,317
December 31, 2022	93,321
December 31, 2023	62,920
December 31, 2024	33,692
Secured term loan facility | Loan and security agreement
Long-Term Debt
Borrowing		$ 100,000
Interest rate (as a percent)		9.50%		12.00%
Term Loan facility
Principal payments of long term debt
Incremental term loan	137,700
Term Loan facility | United Hydrogen Group Inc
Principal payments of long term debt
Incremental term loan	$ 9,500
Generate Lending, LLC | Secured term loan facility | Loan and security agreement
Long-Term Debt
Loan Amount					$ 100,000

Convertible Senior Notes - Net

Convertible Senior Notes - Net proceeds (Details)	Jan. 07, 2021USD ($)shares	May 18, 2020USD ($)D$ / shares	Jan. 31, 2021USD ($)shares	Nov. 30, 2020$ / sharesshares	Aug. 31, 2020$ / sharesshares	May 31, 2020USD ($)shares	Sep. 30, 2019USD ($)shares	Sep. 30, 2021USD ($)$ / sharesshares	Jun. 30, 2021shares	Mar. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)shares	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)	Jan. 01, 2021	May 29, 2020USD ($)	Mar. 31, 2018USD ($)
Convertible Senior Notes
Interest rate (as a percent)														3.75%
Net proceeds												$ 53,447,000	$ 47,568,000
Aggregate consideration													90,238,000
Conversion of convertible senior notes to common stock												15,345,000
Convertible senior note													43,058,000
Proceeds from issuance of convertible senior notes, net													205,098,000
Gain on extinguishment of debt													$ 13,222,000
Closing stock price on grant date | $ / shares				$ 22.25	$ 10.25
Common stock shares issued | shares				43,700,000	35,276,250
3.75% Convertible Senior Notes
Convertible Senior Notes
Principal amount		$ 200,000,000				$ 212,463,000		$ 197,278,000		$ 15,200,000		$ 197,278,000			$ 12,500,000
Interest rate (as a percent)		3.75%				3.75%		3.75%				3.75%			3.75%
Net proceeds						$ 189,219,000
Conversion of notes through common stock issuance | shares								0	0	3,016,036		3,000,000
Maturity principal amount		$ 1,000
Conversion rates for the notes (in shares)		198.6196
Conversion price, per share | $ / shares		$ 5.03
Convertible senior note												$ 15,200,000
Trading days | D		20
Consecutive trading days | D		30
Conversion price (as a percent)		130.00%
Number of business days		5 days
Number of consecutive trading days		5 days
Principal amount (as a percent)		98.00%
Percentage of principal amount to be redeemed		100.00%
Effective interest rate (as a percent)								4.50%				4.50%
Transaction costs for issuance		$ 7,000,000
Initial purchasers' discount		6,400,000				6,374,000
Other issuance costs		$ 600,000				$ 617,000
Closing stock price on grant date | $ / shares								$ 25.54				$ 25.54
Fair value of convertible senior notes								$ 1,000,000,000				$ 1,000,000,000
3.75% Convertible Senior Notes | Minimum
Convertible Senior Notes
Redemption notice days		1 day
3.75% Convertible Senior Notes | Maximum
Convertible Senior Notes
Redemption notice days		3 days
7.5% Convertible Senior Note
Convertible Senior Notes
Interest rate (as a percent)							7.50%						7.50%
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount	$ 160,000	$ 100,000,000	$ 160,000				$ 40,000,000				$ 33,500,000					$ 100,000,000
Interest rate (as a percent)	5.50%	5.50%	5.50%			5.50%	7.50%	5.50%			5.50%	5.50%	5.50%			5.50%
Repurchase of convertible senior notes | shares						9,400,000
Aggregate repurchase of debt						$ 128,900,000
Aggregate consideration						90,200,000
Conversion of notes through common stock issuance | shares	69,808		69,808				16,000,000				14,600,000
Maturity principal amount						66,300,000
Gain on early debt extinguishment						$ 13,200,000
Gain on extinguishment of debt											$ 4,500,000

Convertible Senior Notes - Conv

Convertible Senior Notes - Conversion (Details) - USD ($)	May 18, 2020	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021	Jan. 31, 2021	Jan. 07, 2021	Dec. 31, 2020	May 29, 2020	Sep. 30, 2019	Mar. 31, 2018
Convertible Senior Notes
Net proceeds			$ 53,447,000	$ 47,568,000
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount	$ 100,000,000					$ 160,000	$ 160,000	$ 33,500,000		$ 40,000,000	$ 100,000,000
3.75% Convertible Senior Notes
Convertible Senior Notes
Principal amount	200,000,000	$ 212,463,000	$ 197,278,000		$ 15,200,000				$ 12,500,000
Less initial purchasers' discount	(6,400,000)	(6,374,000)
Less cost of related capped calls		(16,253,000)
Less other issuance costs	$ (600,000)	(617,000)
Net proceeds		$ 189,219,000

Convertible Senior Notes (Detai

Convertible Senior Notes (Details) - USD ($)	Sep. 30, 2021	Mar. 31, 2021	Jan. 31, 2021	Jan. 07, 2021	Dec. 31, 2020	May 31, 2020	May 29, 2020	May 18, 2020	Sep. 30, 2019	Mar. 31, 2018
Convertible Senior Notes
Net carrying amount	$ 192,320,000				$ 85,640,000
3.75% Convertible Senior Notes
Convertible Senior Notes
Principal amount	197,278,000	$ 15,200,000				$ 212,463,000	$ 12,500,000	$ 200,000,000
Unamortized debt issuance costs	(4,958,000)
Net carrying amount	$ 192,320,000
5.5% Convertible Senior Notes
Convertible Senior Notes
Principal amount			$ 160,000	$ 160,000	$ 33,500,000			$ 100,000,000	$ 40,000,000	$ 100,000,000

Convertible Senior Notes - Expe

Convertible Senior Notes - Expenses and Interest (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Amortization of debt issuance costs and discount on convertible senior notes	$ 2,371	$ 12,183
3.75% Convertible Senior Notes
Debt Instrument [Line Items]
Interest expense	1,849
Amortization of debt issuance costs and discount on convertible senior notes	306
Total	$ 2,155
Effective interest rate (as a percent)	4.50%

Convertible Senior Notes - Capp

Convertible Senior Notes - Capped Call and Common Stock Forward (Details) - USD ($)	May 18, 2020	Nov. 30, 2020	Aug. 31, 2020	May 31, 2020	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2021	Mar. 31, 2021	Jan. 31, 2021	Jan. 07, 2021	Jan. 01, 2021	Sep. 30, 2020	May 29, 2020	Sep. 30, 2019	Mar. 31, 2018
Capped Call and Common Stock Forward
Interest rate (as a percent)											3.75%
Share Price		$ 22.25	$ 10.25
Common stock shares issued		43,700,000	35,276,250
Common Stock Forward
Capped Call and Common Stock Forward
Net cost incurred							$ 27,500,000
Number of shares settled					0	4,400,000	8,100,000
3.75% Convertible Senior Notes
Capped Call and Common Stock Forward
Interest rate (as a percent)	3.75%			3.75%	3.75%		3.75%						3.75%
Principal amount	$ 200,000,000			$ 212,463,000	$ 197,278,000		$ 197,278,000	$ 15,200,000					$ 12,500,000
Share Price					$ 25.54		$ 25.54
Convertible senior notes					$ 1,000,000,000		$ 1,000,000,000
Percentage of principal amount to be redeemed	100.00%
3.75% Convertible Senior Notes | Capped Call
Capped Call and Common Stock Forward
Capped call options amount	$ 16,200,000
Cap price	$ 6.7560
Premium (as a percent)	60.00%
Share Price	$ 4.11
5.5% Convertible Senior Notes
Capped Call and Common Stock Forward
Interest rate (as a percent)	5.50%			5.50%	5.50%	5.50%	5.50%		5.50%	5.50%		5.50%		7.50%	5.50%
Principal amount	$ 100,000,000					$ 33,500,000			$ 160,000	$ 160,000				$ 40,000,000	$ 100,000,000
5.5% Convertible Senior Notes | Capped Call
Capped Call and Common Stock Forward
Capped call options amount				$ 16,000,000
Recorded in additional paid-in capital				$ 24,200,000
Percentage of principal amount to be redeemed				100.00%
5.5% Convertible Senior Notes | Common Stock Forward
Capped Call and Common Stock Forward
Common stock shares issued							14,397,906

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock and Warrants (Details) $ / shares in Units, $ in Thousands	Apr. 13, 2020USD ($)	Feb. 28, 2021USD ($)$ / sharesshares	Nov. 30, 2020USD ($)$ / sharesshares	Aug. 31, 2020USD ($)$ / sharesshares	Feb. 28, 2021USD ($)$ / sharesshares	Sep. 30, 2021$ / sharesshares	Sep. 30, 2021USD ($)item$ / sharesshares	Sep. 30, 2020USD ($)	Dec. 31, 2020$ / sharesshares	Dec. 31, 2017shares
Stockholders' equity
Preferred stock, Shares authorized						5,000,000	5,000,000
Preferred stock, par value | $ / shares						$ 0.01	$ 0.01
Net proceeds from shares of common stock sold | $			$ 927,300	$ 344,400			$ 3,587,830	$ 344,398
Common Stock, Shares, Issued						593,077,995	593,077,995		473,977,469
Common stock, par value (in dollars per share) | $ / shares						$ 0.01	$ 0.01		$ 0.01
Number of votes per share | item							1
Common stock shares issued			43,700,000	35,276,250
Share price (in dollars per share) | $ / shares			$ 22.25	$ 10.25
Number of warrants exercised (in shares)						3,501,640	24,736,559
Proceeds from exercise of warrants, net of transaction costs | $							$ 15,445
Series A Junior Participating Cumulative Preferred Stock
Stockholders' equity
Preferred stock, par value | $ / shares						$ 0.01	$ 0.01
Common Stock Shares, Outstanding						0	0		0
SK Holdings Co LTD
Stockholders' equity
Net proceeds from shares of common stock sold | $		$ 1,600,000
Common stock shares issued		54,966,188
Per share price of shares of common stock | $ / shares		$ 29.2893			$ 29.2893
At Market Issuance Sales Agreement
Stockholders' equity
Authorized amount | $	$ 75,000
Public Offerings
Stockholders' equity
Net proceeds from shares of common stock sold | $					$ 2,000,000
Common stock shares issued					32,200,000
Share price (in dollars per share) | $ / shares		$ 65			$ 65
Warrant Issued With Amazon And Walmart Stores Inc Transaction Agreement In 2017
Stockholders' equity
Number of warrants were vested and exercisable							68,380,913		68,380,913
Maximum | Warrant Issued With Amazon And Walmart Stores Inc Transaction Agreement In 2017
Stockholders' equity
Class of Warrant or Right Issued										110,573,392

Warrant Transaction Agreement_2

Warrant Transaction Agreements - Amazon.com, Inc. Transaction Agreement (Details) $ / shares in Units, $ in Thousands	Dec. 31, 2020USD ($)$ / sharesshares	Nov. 02, 2020USD ($)installment$ / sharesshares	Jan. 01, 2019USD ($)installmentshares	Apr. 04, 2017USD ($)shares	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Class of Warrant or Right [Line Items]
Number of warrants exercised (in shares) | shares					3,501,640		24,736,559
Selling, general and administrative					$ 42,421	$ 17,210	$ 106,652	$ 49,963
Provision for loss contracts related to service							(9,586)	(25,110)
Risk-free interest rate	0.58%	0.58%							0.58%
Volatility	75.00%	75.00%							75.00%
Expected average term		6 years 5 months 1 day							6 years 3 months 3 days
Exercise price | $ / shares	$ 13.81	$ 13.81							$ 13.81
Stock price | $ / shares	$ 33.91	15.47							$ 33.91
Warrant Transaction Agreements
Class of Warrant or Right [Line Items]
Shares of common stock that can be purchased from warrants issued (in shares) | shares				55,286,696
Reduction in revenue					$ 106	$ 17,300	$ 315	$ 22,000
Number of warrants exercised (in shares) | shares					3,501,640		17,461,994
Warrant shares vested (in shares) | shares	55,286,696								55,286,696
Fair value of warrants per share | $ / shares		$ 10.57							$ 26.95
Tranche one of warrants issued with the Amazon.com, Inc transaction agreement
Class of Warrant or Right [Line Items]
Shares of common stock that can be purchased from warrants issued (in shares) | shares				5,819,652
Cash payments to be received under agreement				$ 600,000
Selling, general and administrative				$ 6,700
Exercise price calculation							$1.1893
Tranche two of warrants issued with the Amazon.com, Inc. Transaction Agreement
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement			$ 50,000
Reduction in revenue									$ 9,000	$ 4,100	$ 9,800
Warrant shares vested (in shares) | shares			29,098,260
Number of installments | installment			4
Tranche two of warrants issued with the Amazon.com, Inc. Transaction Agreement | Maximum
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement			$ 200,000
Tranche three of warrants issued with the Amazon.com, Inc. Transaction Agreement
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement		$ 50,000
Reduction in revenue	$ 399,700								24,100
Warrant shares vested (in shares) | shares		20,368,784
Number of installments | installment		8
Exercise price of warrants (in dollars per share) | $ / shares					$ 13.81		$ 13.81
Fair value of warrants per share | $ / shares		$ 10.57
Warrant percentage weighted average share price							90.00%
Tranche three of warrants issued with the Amazon.com, Inc. Transaction Agreement | Maximum
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement		$ 400,000
Warrant Issued With Amazon
Class of Warrant or Right [Line Items]
Reduction in revenue									$ 399,700
Warrant shares vested (in shares) | shares	5,354,905	12,730,490							5,354,905
Provision for loss contracts related to service									$ 12,800

Warrant Transaction Agreement_3

Warrant Transaction Agreements - Walmart Stores, Inc. Transaction Agreement (Details) $ / shares in Units, $ in Millions	Jul. 20, 2017USD ($)installment$ / sharesshares	Sep. 30, 2021USD ($)shares	Jun. 30, 2021shares	Mar. 31, 2021shares	Dec. 31, 2020shares	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)
Warrant Transaction Agreements
Number of warrants exercised (in shares)		3,501,640					24,736,559
Warrants issued with the Walmart Stores, Inc transaction agreement
Warrant Transaction Agreements
Shares of common stock that can be purchased from warrants issued (in shares)	55,286,696
Reduction in revenue | $		$ 1.2				$ 1.3	$ 4.4	$ 3.2
Cash payments to be received under agreement | $	$ 200
Warrant shares vested (in shares)		13,094,217			13,094,217		13,094,217
Exercise price calculation	The exercise price of the third tranche of Walmart Warrant Shares will be an amount per share equal to ninety percent (90%) of the 30-day volume weighted average share price of the common stock as of the final vesting date of the second tranche of Walmart Warrant Shares, provided that, with limited exceptions, the exercise price for the third tranche will be no lower than $1.1893
Number of warrants exercised (in shares)		0	0	7,274,565	5,819,652		13,094,217
Tranche one of warrants issued with the Walmart Stores Inc transaction agreement
Warrant Transaction Agreements
Reduction in revenue | $	$ 10.9
Warrant shares vested (in shares)	5,819,652
Exercise price of warrants (in dollars per share) | $ / shares	$ 2.1231
Tranche two of warrants issued with the Walmart Stores, Inc. Transaction Agreement
Warrant Transaction Agreements
Cash payments to be received under agreement | $	$ 50
Warrant shares vested (in shares)	29,098,260
Number of installments | installment	4
Number of shares per installment	7,274,565
Tranche three of warrants issued with the Walmart Stores, Inc. Transaction Agreement
Warrant Transaction Agreements
Shares of common stock that can be purchased from warrants issued (in shares)	20,368,784
Cash payments to be received under agreement | $	$ 50
Number of installments | installment	8
Number of shares per installment	2,546,098
Maximum | Warrants issued with the Walmart Stores, Inc transaction agreement
Warrant Transaction Agreements
Cash payments to be received under agreement | $	$ 600
Maximum | Tranche two of warrants issued with the Walmart Stores, Inc. Transaction Agreement
Warrant Transaction Agreements
Cash payments to be received under agreement | $	200
Maximum | Tranche three of warrants issued with the Walmart Stores, Inc. Transaction Agreement
Warrant Transaction Agreements
Cash payments to be received under agreement | $	$ 400

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue
Net revenue	$ 143,922	$ 107,048	$ 340,437	$ 215,862
Sales of fuel cell systems
Revenue
Net revenue	67,032	51,998	152,620	107,515
Sale of hydrogen installations and other infrastructure
Revenue
Net revenue	48,967	31,664	109,429	44,361
Services performed on fuel cell systems and related infrastructure
Revenue
Net revenue	6,677	6,829	18,397	19,586
Power Purchase Agreements
Revenue
Net revenue	9,321	6,629	25,508	19,629
Fuel delivered to customers
Revenue
Net revenue	11,556	9,831	33,804	24,536
Other
Revenue
Net revenue	$ 369	$ 97	$ 679	$ 235

Revenue - Contract balances (De

Revenue - Contract balances (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Revenue
Accounts receivable	$ 132,370	$ 43,041
Contract assets	9,284	18,189
Contract liabilities	115,595	76,285
Other Current Liabilities
Revenue
Contract liabilities	16,700	20,100
Sales of fuel cell systems
Revenue
Contract liabilities	$ 98,900	$ 56,200

Revenue - Changes in contract a

Revenue - Changes in contract assets and contract liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Contract assets
Transferred to receivables from contract assets recognized at the beginning of the period	$ (13,344)
Revenue recognized and not billed as of the end of the period	4,439
Net change in contract assets	(8,905)
Contract liabilities
Increases due to cash received, net of amounts recognized as revenue during the period	91,985
Revenue recognized that was included in the contract liability balance as of the beginning of the period	(52,675)
Net change in contract liabilities	$ 39,310

Revenue - Estimated future reve

Revenue - Estimated future revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Revenue
Total estimated future revenue	$ 464,881
Sales of fuel cell systems
Revenue
Total estimated future revenue	23,819
Sale of hydrogen installations and other infrastructure
Revenue
Total estimated future revenue	58,429
Services performed on fuel cell systems and related infrastructure
Revenue
Total estimated future revenue	105,548
Power Purchase Agreements
Revenue
Total estimated future revenue	212,360
Fuel delivered to customers
Revenue
Total estimated future revenue	62,609
Other
Revenue
Total estimated future revenue	$ 2,116
Maximum | Sales of fuel cell systems
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	1 year
Maximum | Services performed on fuel cell systems and related infrastructure
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	7 years
Maximum | Power Purchase Agreements
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	7 years
Minimum | Services performed on fuel cell systems and related infrastructure
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	5 years
Minimum | Power Purchase Agreements
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	5 years

Revenue - Others (Details)

Revenue - Others (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Revenue
Capitalized contract costs	$ 807	$ 1,300

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jan. 31, 2021	Jan. 07, 2021	Jan. 01, 2021	Dec. 31, 2020	May 31, 2020	May 29, 2020	May 18, 2020	Sep. 30, 2019	Mar. 31, 2018
Income tax benefit	$ 0	$ 6,644,000	$ 0	$ 24,015,000
Interest rate (as a percent)							3.75%
Giner ELX, Inc
Income tax benefit				$ 5,000,000
3.75% Convertible Senior Notes
Interest rate (as a percent)	3.75%		3.75%						3.75%	3.75%	3.75%
5.5% Convertible Senior Notes
Interest rate (as a percent)	5.50%	5.50%	5.50%	5.50%	5.50%	5.50%		5.50%	5.50%		5.50%	7.50%	5.50%

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Fair Value Measurements
Assets, transfers from level 1 to level 2	$ 0
Assets, transfers from level 2 to level 1	0
Asset transfer into Level 3	0
Asset transfer out of Level 3	0
Liabilities, transfers from level 1 to level 2	0
Liabilities, transfers from level 2 to level 1	0
Liabilities transfer into Level 3	0
Liabilities transfer out of Level 3	$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value
Assets, Carrying Amount	$ 5,740,100	$ 2,251,282
Liabilities, Carrying amount	1,033,211	784,363
Recurring basis | Level 1 | Cash and cash equivalents
Fair Value
Assets, Fair Value	140,574
Recurring basis | Level 1 | U.S. Treasuries
Fair Value
Assets, Fair Value	169,878
Recurring basis | Level 1 | Equity securities
Fair Value
Assets, Fair Value	147,649
Recurring basis | Level 2 | Convertible senior notes
Fair Value
Liabilities, Fair value	1,006,639	1,272,766
Recurring basis | Level 2 | Cash and cash equivalents
Fair Value
Assets, Fair Value	470,077
Recurring basis | Level 2 | Corporate bonds
Fair Value
Assets, Fair Value	530,089
Recurring basis | Level 2 | Commercial paper
Fair Value
Assets, Fair Value	35,795
Recurring basis | Level 2 | Certificates of deposit
Fair Value
Assets, Fair Value	17,004
Recurring basis | Level 3 | Contingent consideration
Fair Value
Liabilities, Fair value	18,520	9,760
Recurring basis | Level 3 | Long-term debt
Fair Value
Liabilities, Fair value	147,255	175,402
Recurring basis | Level 3 | Finance obligations
Fair Value
Liabilities, Fair value	207,837	181,553
Carrying value | Recurring basis | Contingent consideration
Fair Value
Liabilities, Carrying amount	18,520	9,760
Carrying value | Recurring basis | Convertible senior notes
Fair Value
Liabilities, Carrying amount	192,320	85,640
Carrying value | Recurring basis | Long-term debt
Fair Value
Liabilities, Carrying amount	147,255	175,402
Carrying value | Recurring basis | Finance obligations
Fair Value
Liabilities, Carrying amount	207,837	181,553
Carrying value | Recurring basis | Cash and cash equivalents
Fair Value
Assets, Carrying Amount	610,651
Carrying value | Recurring basis | Corporate bonds
Fair Value
Assets, Carrying Amount	530,089
Carrying value | Recurring basis | Commercial paper
Fair Value
Assets, Carrying Amount	35,795
Carrying value | Recurring basis | U.S. Treasuries
Fair Value
Assets, Carrying Amount	169,878
Carrying value | Recurring basis | Certificates of deposit
Fair Value
Assets, Carrying Amount	17,004
Carrying value | Recurring basis | Equity securities
Fair Value
Assets, Carrying Amount	147,649
Fair value | Recurring basis | Contingent consideration
Fair Value
Liabilities, Fair value	18,520	9,760
Fair value | Recurring basis | Convertible senior notes
Fair Value
Liabilities, Fair value	1,006,639	1,272,766
Fair value | Recurring basis | Long-term debt
Fair Value
Liabilities, Fair value	147,255	175,402
Fair value | Recurring basis | Finance obligations
Fair Value
Liabilities, Fair value	207,837	$ 181,553
Fair value | Recurring basis | Cash and cash equivalents
Fair Value
Assets, Fair Value	610,651
Fair value | Recurring basis | Corporate bonds
Fair Value
Assets, Fair Value	530,089
Fair value | Recurring basis | Commercial paper
Fair Value
Assets, Fair Value	35,795
Fair value | Recurring basis | U.S. Treasuries
Fair Value
Assets, Fair Value	169,878
Fair value | Recurring basis | Certificates of deposit
Fair Value
Assets, Fair Value	17,004
Fair value | Recurring basis | Equity securities
Fair Value
Assets, Fair Value	$ 147,649

Operating and Finance Lease L_3

Operating and Finance Lease Liabilities - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Rental expense for all operating lease	$ 9,600	$ 8,100	$ 25,800	$ 20,600
Gross profit on sale leaseback transactions	30,700	25,200	66,100	44,900
Right of use assets obtained in exchange for new operating lease liabilities	26,600	24,600	62,500	32,700
Right of use assets, operating lease	200,200		200,200		$ 136,900
Amortization of right-of-use asset from operating lease	32,300		32,300		19,900
Right of use assets, finance lease	22,800		22,800		5,700
Amortization of right-of-use asset from finance lease	757		757		102
Prepaid rent and security deposit	3,300		3,300		$ 5,800
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	$ 5,800	$ 0	$ 17,900	$ 686
Minimum
Lessee, Lease, Description [Line Items]
Lease Term - as Lessee	1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease Term - as Lessee	9 years		9 years

Operating and Finance Lease L_4

Operating and Finance Lease Liabilities - Future minimum lease payments under operating and finance leases (Details) $ in Thousands	Sep. 30, 2021USD ($)
Future minimum lease payments under operating lease
Remainder of 2021	$ 9,929
2022	39,932
2023	39,989
2024	39,957
2025 and thereafter	90,241
Total future minimum lease payments	220,048
Less imputed lease interest	(57,364)
Total operating lease, liabilities	162,684
Future minimum lease payments under finance leases
Remainder of 2021	1,019
2022	4,012
2023	3,989
2024	3,996
2025 and thereafter	10,843
Total future minimum lease payments	23,859
Less imputed lease interest	(4,074)
Total finance lease liabilities	19,785
Future minimum lease payments under operating and finance leases
Remainder of 2021	10,948
2022	43,944
2023	43,978
2024	43,953
2025 and thereafter	101,084
Total future minimum payments	243,907
Less imputed interest	(61,438)
Total	$ 182,469

Operating and Finance Lease L_5

Operating and Finance Lease Liabilities - Other information related to the operating leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Lessee, Operating Lease, Description [Abstract]
Cash payments	$ 25,726	$ 14,954
Weighted average remaining lease term (in years)	5 years 8 months 19 days	4 years 6 months 18 days
Weighted average discount rate (as a percent)	11.20%	11.80%

Operating and Finance Lease L_6

Operating and Finance Lease Liabilities - Other information related to the finance leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Other information
Cash payments	$ 2,128	$ 252
Weighted average remaining lease term (years)	4 years 6 months 25 days	6 years 6 months 3 days
Weighted average discount rate	6.90%	9.60%

Finance Obligations - Narrative

Finance Obligations - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Sale Leaseback Transaction [Line Items]
Total operating lease, liabilities	$ 162,684
Short term operating lease obligation	23,284	$ 14,314
Long term operating lease obligation	139,400	99,624
Total finance lease liabilities	19,785
Short term finance lease obligation	2,758	903
Long term finance lease obligation	17,027	4,493
Sale Leaseback Agreements
Sale Leaseback Transaction [Line Items]
Total finance lease liabilities	17,299	23,900
Short term finance lease obligation	5,100	8,000
Long term finance lease obligation	12,200	15,900
Sale Leaseback Agreements | Future Services [Member]
Sale Leaseback Transaction [Line Items]
Total finance lease liabilities	190,500	157,700
Short term finance lease obligation	30,500	24,200
Long term finance lease obligation	$ 160,000	$ 133,500

Finance Obligations - Future mi

Finance Obligations - Future minimum payments under finance obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Future minimum lease payments under finance leases
Remainder of 2021	$ 1,019
2022	4,012
2023	3,989
2024	3,996
2025 and thereafter	10,843
Total future minimum lease payments	23,859
Less imputed lease interest	(4,074)
Total finance lease liabilities	19,785
Finance obligation
Future minimum lease payments under finance leases
Remainder of 2021	14,468
2022	55,607
2023	53,780
2024	66,786
2025 and thereafter	86,614
Total future minimum lease payments	277,255
Less imputed lease interest	(69,418)
Total finance lease liabilities	207,837
Sale of Future Revenue - Debt
Future minimum lease payments under finance leases
Remainder of 2021	12,788
2022	50,632
2023	50,632
2024	50,632
2025 and thereafter	86,614
Total future minimum lease payments	251,298
Less imputed lease interest	(60,760)
Total finance lease liabilities	190,538
Sale Leaseback Agreements
Future minimum lease payments under finance leases
Remainder of 2021	1,680
2022	4,975
2023	3,148
2024	16,154
Total future minimum lease payments	25,957
Less imputed lease interest	(8,658)
Total finance lease liabilities	$ 17,299	$ 23,900

Finance Obligations - Other inf

Finance Obligations - Other information related to finance obligations (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Sale Leaseback Transaction [Line Items]
Cash payments	$ 2,128	$ 252
Weighted average remaining term (years)	4 years 6 months 25 days	6 years 6 months 3 days
Weighted average discount rate	6.90%	9.60%
Finance obligation
Sale Leaseback Transaction [Line Items]
Cash payments	$ 41,325	$ 31,693
Weighted average remaining term (years)	4 years 10 months 17 days	4 years 8 months 26 days
Weighted average discount rate	11.30%	11.30%

Investments - Available-for-sal

Investments - Available-for-sale securities (Details) $ in Thousands	Sep. 30, 2021USD ($)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 756,841
Gross Unrealized Gains	170
Gross Unrealized Losses	(4,245)
Fair Value	752,766
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	533,691
Gross Unrealized Gains	93
Gross Unrealized Losses	(3,695)
Fair Value	530,089
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,719
Gross Unrealized Gains	76
Fair Value	35,795
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,017
Gross Unrealized Losses	(13)
Fair Value	17,004
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	170,414
Gross Unrealized Gains	1
Gross Unrealized Losses	(537)
Fair Value	$ 169,878

Investments - Equity Securities

Investments - Equity Securities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Cost	$ 147,933
Gross Unrealized Losses	(284)
Fair Value	147,649
Fixed income mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	77,766
Gross Unrealized Losses	(132)
Fair Value	77,634
Exchange traded mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Cost	70,167
Gross Unrealized Losses	(152)
Fair Value	$ 70,015

Investments - Contractual Matur

Investments - Contractual Maturity (Details) $ in Thousands	Sep. 30, 2021USD ($)
Amortized Cost
Within one year	$ 447,479
After one through five years	309,362
Amortized Cost	756,841
Fair Value
Within one year	446,011
After one through five years	306,755
Total available-for-sale securities	752,766
Accrued interest income	$ 4,900

Commitments and Contingencies -

Commitments and Contingencies - Concentrations of Credit Risk (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021USD ($)customer	Sep. 30, 2020	Sep. 30, 2021USD ($)customer	Sep. 30, 2020	Dec. 31, 2020customer
Customer Concentration
Federal depository insurance coverage	$ 250		$ 250
Restricted cash	301,300		301,300
Letter of Credit
Customer Concentration
Restricted Cash	$ 137,700		$ 137,700
Accounts receivable | Customer concentration | One customers
Customer Concentration
Number of customers | customer	1		1
Concentration risk (as a percent)			79.60%
Accounts receivable | Customer concentration | Three customers
Customer Concentration
Number of customers | customer					3
Concentration risk (as a percent)					73.90%
Revenues | Customer concentration | Two customers
Customer Concentration
Concentration risk (as a percent)		83.00%		71.80%
Revenues | Customer concentration | Three customers
Customer Concentration
Concentration risk (as a percent)	80.10%		80.60%

Employee Benefit Plans - Assump

Employee Benefit Plans - Assumptions For Estimating Fair Value (Details) - USD ($) $ / shares in Units, $ in Millions	May 12, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jul. 31, 2021	Nov. 30, 2020	Aug. 31, 2020	May 12, 2011
Assumptions for estimating fair value
Closing stock price on grant date							$ 22.25	$ 10.25
Service Options Awards
Employee Benefit Plans
Compensation cost		$ 4.2	$ 1.1	$ 11.9	$ 4.1
Options granted				1,870,835	3,429,549
Assumptions for estimating fair value
Expected term of options (years)					6 years
Risk Free interest rate, minimum (as a percent)				0.61%	0.37%
Risk Free interest rate, maximum (as a percent)				1.05%	1.37%
Volatility, minimum (as a percent)				72.46%	64.19%
Volatility, maximum (as a percent)				75.52%	66.94%
Dividend Yield				0.00%
Service Options Awards | Minimum
Assumptions for estimating fair value
Expected term of options (years)				3 years
Service Options Awards | Maximum
Employee Benefit Plans
Options exercisable (as a percent)				200.00%
Assumptions for estimating fair value
Expected term of options (years)				5 years
Performance Option Awards
Employee Benefit Plans
Compensation cost		$ 2		$ 2
Options granted				14,560,000
Assumptions for estimating fair value
Remaining performance period				3 years
Risk free rate (as a percent):				1.12%
Volatility (as a percent):				70.00%
Closing stock price on grant date		$ 26.92		$ 26.92
Employees | Service Options Awards
Employee Benefit Plans
Vesting period				3 years
Expiration period				10 years
Board of Directors | Service Options Awards
Employee Benefit Plans
Vesting period				1 year
the 2011 Plan
Employee Benefit Plans
Maximum number of common stock shares available for issuance						473,491
Compensation cost		$ 12.7	$ 2.3	$ 32.3	$ 7.3
the 2011 Plan | Stock options outstanding
Employee Benefit Plans
Maximum number of common stock shares available for issuance		42,400,000		42,400,000					1,000,000
Options granted	0
2021 Stock Option Incentive Plan
Employee Benefit Plans
Number of options available for issuance (in shares)						22,500,000
Stock Incentive Plan 2011 And 2021 | Service Options Awards
Employee Benefit Plans
Expiration period				10 years
Stock Incentive Plan 2011 And 2021 | Service Options Awards | Minimum
Employee Benefit Plans
Vesting period				1 year
Stock Incentive Plan 2011 And 2021 | Service Options Awards | Maximum
Employee Benefit Plans
Vesting period				3 years

Employee Benefit Plans - Stock

Employee Benefit Plans - Stock Activity, Weighted Average Exercise Price (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Service Options Awards
Shares
Options outstanding, beginning balance (in shares)			10,284,498
Granted (in shares)			1,870,835	3,429,549
Exercised (in shares)			(1,911,112)
Forfeited (in shares)			(15,833)
Expired (in shares)			(4,100)
Options outstanding, end balance (in shares)	10,224,288		10,224,288		10,284,498
Options exercisable (in shares)	5,045,168		5,045,168
Options unvested (in shares)	5,179,120		5,179,120
Weighted Average Exercise Price
Options outstanding, beginning balance, weighted-average exercise price			$ 5.78
Granted, weighted-average exercise price			32.48
Exercised, weighted-average exercise price			2.78
Forfeited, weighted-average exercise price			21.35
Expired, weighted-average exercise price			6.10
Options outstanding, end balance, weighted-average exercise price	$ 11.21		11.21		$ 5.78
Options exercisable, weighted-average exercise price	4.46		4.46
Options unvested, weighted-average exercise price	$ 17.77		$ 17.77
Stock option activity additional disclosures
Options outstanding, weighted-average remaining contractual term			7 years 10 months 24 days		7 years 9 months 18 days
Options exercisable, weighted-average remaining contractual term			6 years 8 months 12 days
Options unvested, weighted-average remaining contractual term			9 years
Options outstanding, aggregate intrinsic value	$ 146,581		$ 146,581		$ 289,316
Options exercisable, aggregate intrinsic value	106,360		106,360
Options unvested, aggregate intrinsic value	$ 40,221		$ 40,221
Weighted-average grant date fair value of options granted (per share)	$ 15.82	$ 7.45	$ 19.76	$ 7.21
Fair value of stock options that vested during the period	$ 10,400	$ 5,200	$ 10,900	$ 5,900
Compensation cost	4,200	1,100	11,900	4,100
Unrecognized compensation cost	$ 50,200	$ 8,200	$ 50,200	$ 8,200
Period for recognition			3 years
Performance Option Awards
Shares
Granted (in shares)			14,560,000
Options outstanding, end balance (in shares)	14,560,000		14,560,000
Options unvested (in shares)	14,560,000		14,560,000
Weighted Average Exercise Price
Granted, weighted-average exercise price			$ 26.92
Options outstanding, end balance, weighted-average exercise price	$ 26.92		26.92
Options unvested, weighted-average exercise price	26.92		$ 26.92
Stock option activity additional disclosures
Options outstanding, weighted-average remaining contractual term			6 years 11 months 23 days
Options unvested, weighted-average remaining contractual term			6 years 11 months 23 days
Weighted-average grant date fair value of options granted (per share)	$ 12.78		$ 12.78
Fair value of stock options that vested during the period	$ 0		$ 0
Compensation cost	2,000		2,000
Unrecognized compensation cost	$ 183,700		$ 183,700
Period for recognition			3 years

Employee Benefit Plans - Restri

Employee Benefit Plans - Restricted Stock Activity (Details) - Restricted stock outstanding - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Benefit Plans
Compensation cost	$ 6,500	$ 1,200	$ 18,500	$ 3,200
Unrecognized compensation cost	$ 81,200	$ 6,200	$ 81,200	$ 6,200
Period for recognition			3 years
Shares
Unvested restricted stock, beginning balance (in shares)			5,874,642
Granted (in shares)			1,812,856
Vested (in shares)			(2,713,789)
Forfeited (in shares)			(13,333)
Unvested restricted stock, end balance (in shares)	4,960,376		4,960,376
Aggregate Intrinsic Value
Unvested restricted stock aggregate intrinsic value	$ 126,688		$ 126,688
Minimum
Employee Benefit Plans
Vesting period			1 year
Maximum
Employee Benefit Plans
Vesting period			3 years

Employee Benefit Plans - 401(K)

Employee Benefit Plans - 401(K) Saving And Retirement Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Non Employee Director
Non-Employee Benefit Plan Compensation
Granted (in shares)	3,685	4,146	8,923	26,636
Compensation cost	$ 99	$ 56	$ 277	$ 167
Savings And Retirement Plan 401 K
401(K) Savings & Retirement Plan
Percent of salary employee is permitted to contribute			100.00%
Vesting period			3 years
Common stock, shares issued			54,531	368,903
Total expense (including issuance of shares)	$ 1,100	$ 600	$ 3,400	$ 1,900

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent event € in Millions, $ in Millions	Oct. 14, 2021USD ($)	Nov. 30, 2021EUR (€)
Frames Group [Member]
Subsequent Events
Purchase price | €		€ 115
Value of future earnouts given for acquisition | €		€ 30
Applied Cryo Technologies [Member]
Subsequent Events
Purchase price	$ 170
Value of stock given for acquisition	40
Value of future earnouts given for acquisition	$ 30