Revenue - Estimated future revenue (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Revenue
Total estimated future revenue	$ 367,406
Sales of fuel cell systems
Revenue
Total estimated future revenue	16,209
Sale of hydrogen installations and other infrastructure
Revenue
Total estimated future revenue	28,282
Services performed on fuel cell systems and related infrastructure
Revenue
Total estimated future revenue	75,467
Power Purchase Agreements
Revenue
Total estimated future revenue	178,450
Fuel delivered to customers
Revenue
Total estimated future revenue	65,704
Other
Revenue
Total estimated future revenue	$ 3,294
Maximum | Sales of fuel cell systems
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	1 year
Maximum | Services performed on fuel cell systems and related infrastructure
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	7 years
Maximum | Power Purchase Agreements
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	7 years
Minimum | Services performed on fuel cell systems and related infrastructure
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	5 years
Minimum | Power Purchase Agreements
Revenue
Duration of estimated revenue expected to be recognized in future (in years)	5 years