Revenue - Estimated future revenue (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Revenue
Total estimated future revenue	$ 393,790
Sales of fuel cell systems
Revenue
Total estimated future revenue	71,402
Sale of hydrogen installations and other infrastructure
Revenue
Total estimated future revenue	71,753
Services performed on fuel cell systems and related infrastructure
Revenue
Total estimated future revenue	94,725
Power Purchase Agreements
Revenue
Total estimated future revenue	151,793
Other
Revenue
Total estimated future revenue	$ 4,117
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