Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Summary of Significant Accounting Policies
Upfront revenue recognized	$ 0
Capitalized contract costs	100		$ 0
Net Cash Provided by (Used in) Financing Activities	48,942	$ 32,208
ASU 2016-18
Summary of Significant Accounting Policies
Net Cash Provided by (Used in) Financing Activities	2,800	2,600
Decrease in cash and cash equivalents	2,800	$ 2,600
Proforma adjustment | ASU 2016-02
Summary of Significant Accounting Policies
Increase in finance obligation	$ 30,000
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%
Total project costs (as a percent)	30.00%
Amortization period of capitalized commission fees	5 years
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%
Total project costs (as a percent)	50.00%
Amortization period of capitalized commission fees	10 years