Derivative Financial Instruments - Australia Ravenhall (Details) AUD in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 AUD	Mar. 31, 2017 USD ($)
Derivative [Line Items]
Unrealized losses, net of tax, related to cash flow hedge	$ 479,000	$ 2,444,000
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				$ 19,200,000
Ravenhall, Australia | Design and construction phase | Interest Rate Swap
Derivative [Line Items]
Fixed interest rate on derivative			3.30%	3.30%
Notional amount coincide with the terms of the non-recourse debt			AUD 643	$ 492,000,000
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			AUD 466	$ 356,000,000
Ravenhall, Australia | Cash Flow Hedge
Derivative [Line Items]
Unrealized losses, net of tax, related to cash flow hedge	$ 500,000
Construction Facility | Non-Recourse Debt | National Australia Bank Limited | Ravenhall
Derivative [Line Items]
Lump sum due at completion			AUD 310	$ 237,000,000