Derivative Financial Instruments (Australia Ravenhall) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 AUD
Derivative [Line Items]
Change in fair value of derivative instrument classified as cash flow hedge	$ 1,820	$ (1,375)	$ (16,048)
Payments on non-recourse debt	10,064	$ 11,908	$ 18,627
Interest Rate Swap | Asset under Construction | Ravenhall, Australia
Derivative [Line Items]
Fixed interest rate on cash flow interest rate derivative			3.30%
Notional amount	516,000			AUD 716,000,000
Interest Rate Swap | Operating Phase of Asset | Ravenhall, Australia
Derivative [Line Items]
Fixed interest rate on cash flow interest rate derivative			4.20%
Notional amount	336,000			466,000,000
Interest Rate Cap | Ravenhall, Australia
Derivative [Line Items]
Payments on non-recourse debt	1,700
Decrease in fair value of interest rate cap assets	(100)
National Australia Bank Limited | Non Recourse Debt | Ravenhall
Derivative [Line Items]
Lump sum due at completion	224,000			AUD 310,000,000
Cash Flow Hedging | Ravenhall, Australia
Derivative [Line Items]
Change in fair value of derivative instrument classified as cash flow hedge	1,800
Other Noncurrent Liabilities | Ravenhall, Australia
Derivative [Line Items]
Value of swap liability	$ 18,700