Revenue - Changes in contract assets and contract liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Contract assets
Net change in contract assets	$ (580)	$ (1,356)
Contract liabilities
Increases due to customer billings, net of amounts recognized as revenue during the period	18,999		$ 74,702
Change in contract liabilities related to warrants	108		440
Revenue recognized that was included in the contract liability balance as of the beginning of the period	(40,804)		(160,819)
Net change in deferred revenue and contract liabilities	(21,697)		(85,677)
Sales of fuel cell systems
Contract assets
Transferred to receivables from contract assets recognized at the beginning of the period	(8,837)		(27,513)
Change in contract assets related to warrants	(1,967)		(4,909)
Impairment			(35,118)
Revenue recognized and not billed as of the end of the period	8,149		29,566
Net change in contract assets	$ (2,655)		$ (37,974)