Long-Term Debt (Details) - NY Green Bank - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jul. 21, 2017	Jun. 30, 2017	Dec. 23, 2016
Debt Instrument [Line Items]
Loan Amount			$ 45.0		$ 25.0
Long-term borrowings					25.0
Debt issuance costs					$ 1.2
Increase in term loan facility			$ 20.0
Prepayment fee (as a percent)	7.50%	7.50%
End of term charge	$ 1.8
Percent of securities in foreign subsidiaries guaranteed to secure debt	65.00%
Secured term loan facility
Debt Instrument [Line Items]
Debt issuance costs		$ 0.5
Long-term Line of Credit	$ 27.3	32.8
Additional amount borrowed		$ 20.0
Effective interest rate (as a percent)	11.80%			11.20%
Term of loan agreement	3 years
2018 (Remainder of fiscal year)	$ 10.2
2019	$ 17.1
Secured term loan facility | LIBOR
Debt Instrument [Line Items]
Interest rate spread (as a percent)	9.50%