Revenue - Estimated future revenue (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)
Revenue
Total estimated future revenue	$ 474,085
Sales of fuel cell systems
Revenue
Total estimated future revenue	55,348
Sale of hydrogen installations and other infrastructure
Revenue
Total estimated future revenue	52,193
Services performed on fuel cell systems and related infrastructure
Revenue
Total estimated future revenue	103,505
Power Purchase Agreements
Revenue
Total estimated future revenue	196,903
Fuel delivered to customers
Revenue
Total estimated future revenue	63,632
Other
Revenue
Total estimated future revenue	$ 2,504
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