Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Sales of fuel cell systems and related infrastructure	$ 29,472	$ 24,777	$ 18,663	$ 5,090	$ 16,081	$ 15,462	$ 13,601	$ 3,162	$ 78,002	$ 48,306	$ 18,446
Services performed on fuel cell systems and related infrastructure	4,929	3,555	2,883	2,645	2,858	2,755	2,729	1,567	14,012	9,909	6,659
Power Purchase Agreements	2,118	1,546	1,077	977	902	639	337	259	5,718	2,137
Fuel delivered to customers	1,744	1,544	1,128	659	738	654	326	241	5,075	1,959
Other	168	10	258	45	874	371	328	346	481	1,919	1,496
Gross (loss) profit	(9,417)	76	1,562	(2,111)	(1,658)	(1,093)	195	(2,306)	(9,890)	(4,862)	(11,248)
Operating expenses	14,703	12,332	11,427	10,650	11,558	9,603	6,837	5,072	49,112	33,070	17,717
Operating loss	(24,120)	(12,256)	(9,865)	(12,761)	(13,216)	(10,696)	(6,642)	(7,378)	(59,002)	(37,932)	(28,965)
Net loss attributable to common shareholders	$ (25,227)	$ (10,238)	$ (9,253)	$ (11,077)	$ (7,183)	$ (9,377)	$ 3,825	$ (75,909)	$ (55,795)	$ (88,644)	$ (62,791)
(Loss) income per share:
Basic and diluted (in dollars per share)	$ (0.14)	$ (0.06)	$ (0.05)	$ (0.06)	$ (0.04)	$ (0.06)	$ 0.02	$ (0.57)	$ (0.32)	$ (0.56)	$ (0.82)
Loss on Contracts	$ 10,100								$ 10,100