Derivative Financial Instruments - Australia Ravenhall (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 AUD ($)	Mar. 31, 2018 USD ($)
Derivative [Line Items]
Unrealized gain, net of tax, related to cash flow hedge	$ 736,000	$ (479,000)
Ravenhall, Australia
Derivative [Line Items]
Ineffective portion of Cash Flow Hedge interest rate swap	0
Ravenhall, Australia | Other Noncurrent Liabilities
Derivative [Line Items]
Fair value of the swap liability				$ 13,100,000
Ravenhall, Australia | Operating phase | Interest Rate Swap
Derivative [Line Items]
Fixed interest rate on derivative			4.20%	4.20%
Notional amount coincide with the terms of the non-recourse debt			$ 466	$ 358,000,000
Ravenhall, Australia | Cash Flow Hedge
Derivative [Line Items]
Unrealized gain, net of tax, related to cash flow hedge	$ 100,000