Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended
	Mar. 08, 2018	Sep. 30, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Upfront revenue recognized				$ 0
Principal amount			$ 100,000
Proceeds from issuance of debt				$ 39,052	$ 95,856
Maturity principal amount		$ 48,000
Minimum
Summary of Significant Accounting Policies
Payment terms for fuel cells and its services				30 days
Extension period				5 years
Uptime of the fleet (as a percent)				97.00%
Maximum
Summary of Significant Accounting Policies
Payment terms for fuel cells and its services				90 days
Extension period				10 years
Uptime of the fleet (as a percent)				98.00%
Convertible Senior Notes
Summary of Significant Accounting Policies
Principal amount		$ 40,000	$ 100,000
Interest rate (as a percent)		7.50%	5.50%
$40M Convertible Senior Note
Summary of Significant Accounting Policies
Principal amount		$ 40,000		$ 48,000
Interest rate (as a percent)		7.50%
Proceeds from issuance of debt		$ 39,100
Percentage of principal amount to be repaid at maturity		120.00%
Maturity principal amount		$ 48,000
Unamortized debt discount		$ 8,000		7,400
$100M Convertible Senior Notes
Summary of Significant Accounting Policies
Principal amount	$ 100,000		$ 100,000	100,000
Interest rate (as a percent)			5.50%
Proceeds from issuance of debt	$ 52,356		$ 95,900
Percentage of principal amount to be repaid at maturity		100.00%
Unamortized debt discount				$ 27,818