Intangible Assets - Gross Carrying Amount (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2019
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Gross Carrying Amount	$ 8,564	$ 6,246
Accumulated Amortization	(3,025)	(2,356)
Total	5,539	3,890
Payments to Acquire Intangible Assets	2,404	929
Payables for acquiring Intellectual Property	14,213	7,864
Amortization of intangible assets	698	$ 693	$ 593
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
Payments to Acquire Intangible Assets	400
Payables for acquiring Intellectual Property	$ 500
Acquired technology
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	10 years	9 years
Gross Carrying Amount	$ 8,244	$ 5,926
Accumulated Amortization	(2,815)	(2,176)
Total	$ 5,429	$ 3,750
Customer relationships
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	10 years	10 years
Gross Carrying Amount	$ 260	$ 260
Accumulated Amortization	(150)	(123)
Total	$ 110	$ 137
Trademark
Gross carrying amount and accumulated amortization of acquired identifiable intangible assets
Weighted Average Amortization Period	5 years	5 years
Gross Carrying Amount	$ 60	$ 60
Accumulated Amortization	$ (60)	(57)
Total		$ 3