Intangible Assets and Goodwill - Gross Carrying Amount (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	$ 43,587	$ 8,564
Accumulated Amortization	(4,336)	(3,025)
Total	39,251	5,539
Goodwill	72,387	8,842	$ 71,822	$ 70,262	$ 8,673	$ 8,606	$ 8,961	$ 8,886
Increase in goodwill		62,600
Translation gain on goodwill		900
Goodwill impairments	0	0
EnergyOr
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Acquired		1,500
Milestone payments		$ 3,000
American Fuel Cell LLC
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Milestone payments	2,900
In process R&D
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	29,000
Total	$ 29,000
Acquired technology
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	10 years	9 years
Gross Carrying Amount	$ 13,697	$ 8,244
Accumulated Amortization	(4,042)	(2,815)
Total	$ 9,655	$ 5,429
Customer relationships, Backlog & Trademark
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	6 years
Gross Carrying Amount	$ 890
Accumulated Amortization	(294)
Total	$ 596
Trademark
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period		9 years
Gross Carrying Amount		$ 320
Accumulated Amortization		(210)
Total		$ 110