Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue
Net revenue	$ 56,376	$ 53,165	$ 132,037	$ 114,812
Sales of fuel cell systems
Revenue
Net revenue	31,264	21,594	72,031	40,948
Sale of hydrogen installations and other infrastructure
Revenue
Net revenue	6,901	15,074	6,901	25,153
Services performed on fuel cell systems and related infrastructure
Revenue
Net revenue	5,920	5,156	17,415	16,330
Power Purchase Agreements
Revenue
Net revenue	5,599	5,555	16,613	16,365
Fuel delivered to customers
Revenue
Net revenue	6,557	$ 5,786	18,942	$ 16,016
Other
Revenue
Net revenue	$ 135		$ 135