Revenue - Changes in contract assets and contract liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Contract assets
Net change in contract assets	$ (1,356)	$ 14,677
Contract liabilities
Increases due to cash received, net of amounts recognized as revenue during the period	12,057		$ 151,965
Change in contract liabilities related to warrants	110		440
Revenue recognized that was included in the contract liability balance as of the beginning of the period	(44,667)		(94,001)
Net change in deferred revenue and contract liabilities	(32,500)		58,404
Sales of fuel cell systems
Contract assets
Transferred to receivables from contract assets recognized at the beginning of the period	(9,082)		(94,860)
Change in contract assets related to warrants	5,850		14,260
Impairment			(2,375)
Revenue recognized and not billed as of the end of the period	7,617		134,677
Net change in contract assets	$ 4,385		$ 51,702