Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Net revenue	$ 91,664	$ 59,461	$ 57,535	$ 21,579	$ 59,820	$ 53,165	$ 35,229	$ 26,418
Net revenue									$ 230,239	$ 174,632	$ 100,153
Sales of fuel cell systems
Revenue
Net revenue									130,721	75,146	49,206
Sale of hydrogen installations and other infrastructure
Revenue
Net revenue									19,163	32,146	13,425
Services performed on fuel cell systems and related infrastructure
Revenue
Net revenue	7,328	6,205	5,341	6,343	5,672	5,156	5,691	5,483	25,217	22,002	16,202
Power Purchase Agreements
Revenue
Net revenue	6,739	6,595	6,409	6,110	6,504	5,555	5,438	5,372	25,853	22,869	12,869
Fuel delivered to customers
Revenue
Net revenue	7,779	7,649	$ 7,089	$ 6,582	$ 6,453	$ 5,786	$ 5,280	$ 4,950	29,099	$ 22,469	8,167
Other
Revenue
Net revenue	$ 51	$ 135							$ 186		$ 284