Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Sales of fuel cell systems and related infrastructure	$ 19,993	$ 5,653	$ 9,121	$ 5,218	$ 29,472	$ 24,777	$ 18,663	$ 5,090	$ 39,985	$ 78,002	$ 48,306
Services performed on fuel cell systems and related infrastructure	5,060	4,763	5,360	5,273	4,929	3,555	2,883	2,645	20,456	14,012	9,909
Sales Revenue, Services, Net	4,061	3,858	3,062	2,706	2,118	1,546	1,077	977	13,687	5,718	2,137
Fuel delivered to customers	3,359	2,909	2,638	2,010	1,744	1,544	1,128	659	10,916	5,075	1,959
Other	105	376	278	125	168	10	258	45	884	481	1,919
Gross (loss) profit	3,011	381	384	170	(9,417)	76	1,562	(2,111)	3,946	(9,890)	(4,862)
Operating expenses	14,948	13,637	13,760	13,120	14,703	12,332	11,427	10,650	55,465	49,112	33,070
Operating loss	(11,937)	(13,256)	(13,376)	(12,950)	(24,120)	(12,256)	(9,865)	(12,761)	(51,519)	(59,002)	(37,932)
Net loss attributable to common shareholders	$ (19,237)	$ (13,420)	$ (13,154)	$ (11,780)	$ (25,227)	$ (10,238)	$ (9,253)	$ (11,077)	$ (57,591)	$ (55,795)	$ (88,644)
(Loss) income per share:
Basic and diluted (in dollars per share)	$ (0.11)	$ (0.07)	$ (0.07)	$ (0.07)	$ (0.14)	$ (0.06)	$ (0.05)	$ (0.06)	$ (0.32)	$ (0.32)	$ (0.56)
Provision			$ 1,100		$ 10,100				$ 1,071	$ (10,050)