Restatement of Previously Issued Consolidated Financial Statements - Research and development expense (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cost of revenue		$ 135,632	$ 68,010	$ 50,522	$ 83,861	$ 54,892	$ 51,324	$ 29,250	$ 118,532	$ 80,574	$ 254,164	$ 135,466	$ 376,179	$ 219,327	$ 200,219
Research and Development Expense		7,386	4,873	4,774	4,882	3,563	3,608	3,006	9,647	6,614	17,033	10,177	27,848	15,059	12,750
Gross Profit	$ (431,114)	(28,584)	(15)	(9,703)	7,746	4,500	6,142	(7,740)	(9,718)	(1,598)	(38,302)	2,902	(469,416)	10,648	(26,004)
Sales of fuel cell systems, related infrastructure and equipment
Cost of revenue		69,428	33,888	13,974	47,091	25,183	23,329	2,312	47,862	25,641	117,290	50,824	171,404	97,915	85,205
Services performed on fuel cell systems and related infrastructure
Cost of revenue		9,180	7,773	10,347	11,606	7,802	8,383	6,791	18,120	15,174	27,300	22,976	42,524	34,582	32,271
Provision (benefit) for loss contracts related to service
Cost of revenue		25,147	706	95	13	206	363	162	801	201	25,948	407	35,473	394	5,345
Power Purchase Agreements
Cost of revenue		14,744	14,504	14,771	12,301	10,814	8,829	9,833	29,275	18,662	44,019	29,476	64,640	41,777	41,361
Fuel delivered to customers
Cost of revenue		17,002	11,076	11,254	12,800	11,149	11,146	10,152	22,330	21,298	39,332	32,447	61,815	45,247	36,037
Other
Cost of revenue		131	63	81	50	150			144		275	150	$ 323	200
Restatement Adjustments
Cost of Revenue														19,492	21,157
Cost of revenue		27,353	5,016	5,238	4,979	3,778	4,410	3,887	10,254	8,297	37,607	12,075		17,054	28,209
Research and Development Expense		(4,578)	(4,884)	(5,638)	(4,459)	(4,465)	(5,325)	(4,367)	(10,522)	(9,692)	(15,100)	(14,157)		(18,616)	(21,157)
Gross Profit		(27,294)	(5,091)	(5,232)	(5,036)	(3,847)	(4,479)	(3,956)	(10,323)	(8,435)	(37,617)	(12,282)		(17,318)	(28,626)
Restatement Adjustments | Sales of fuel cell systems, related infrastructure and equipment
Cost of Revenue														1,121	614
Cost of revenue		919	212	230	672	193	200	(9)	442	191	1,361	384		1,056	766
Restatement Adjustments | Services performed on fuel cell systems and related infrastructure
Cost of Revenue														6,986	7,954
Cost of revenue		2,106	1,282	2,166	1,607	1,341	2,165	668	3,448	2,833	5,554	4,174		5,781	8,573
Restatement Adjustments | Provision (benefit) for loss contracts related to service
Cost of revenue		20,841	706	95	13	206	363	162	801	201	21,642	407		394	5,345
Restatement Adjustments | Power Purchase Agreements
Cost of Revenue														2,539	4,264
Cost of revenue		657	800	528	309	461	116	835	1,328	951	1,985	1,412		1,721	5,200
Restatement Adjustments | Fuel delivered to customers
Cost of Revenue														8,846	8,325
Cost of revenue		2,830	2,016	2,219	2,378	1,989	2,292	2,231	4,235	4,523	7,065	6,512		8,890	8,325
Revision of Research and Development Expense
Research and Development Expense														19,500	21,200
Revision of Research and Development Expense | Sales of fuel cell systems, related infrastructure and equipment
Cost of revenue														7,000
Revision of Research and Development Expense | Fuel delivered to customers
Cost of revenue														8,900
Revision of Research and Development Expense | Restatement Adjustments
Cost of revenue														1,100
Research and Development Expense		(5,500)	(4,900)	(5,600)	(5,300)	(4,500)	(5,300)	(4,400)	(10,500)	(9,700)	(15,900)	(14,200)		(19,492)	(21,157)
Revision of Research and Development Expense | Restatement Adjustments | Sales of fuel cell systems, related infrastructure and equipment
Cost of revenue		232	212	230	585	193	200	143	442	343	674	384			614
Revision of Research and Development Expense | Restatement Adjustments | Services performed on fuel cell systems and related infrastructure
Cost of revenue		1,500	1,600	2,400	1,900	1,600	2,500	971	4,000	3,500	5,500	5,100		$ 2,500	8,000
Revision of Research and Development Expense | Restatement Adjustments | Power Purchase Agreements
Cost of revenue		955	1,100	799	564	654	299	1,000	1,900	1,300	2,800	2,000			4,200
Revision of Research and Development Expense | Restatement Adjustments | Fuel delivered to customers
Cost of revenue		2,800	2,000	2,200	2,300	2,000	2,300	$ 2,200	4,200	4,500	7,000	6,500			$ 8,300
Revision of Loss of Accrual Provision | Restatement Adjustments | Sales of fuel cell systems, related infrastructure and equipment
Cost of revenue											$ (839)
Revision of Loss of Accrual Provision | Restatement Adjustments | Services performed on fuel cell systems and related infrastructure
Cost of revenue		$ 315	$ (315)	$ (224)	$ (289)	$ (288)	$ 369		$ (524)	$ (672)		$ (960)