Derivative Financial Instruments - Australia Ravenhall (Details) AUD in Millions	1 Months Ended	3 Months Ended
	Sep. 30, 2014 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Mar. 31, 2016 AUD	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Unrealized losses, net of tax, related to cash flow hedge		$ (2,444,000)	$ (4,080,000)
Payments on non-recourse debt		1,613,000	$ 1,645,000
Ravenhall, Australia
Derivative [Line Items]
Ineffective portion of Cash Flow Hedge interest rate swap		0
Ravenhall, Australia | Interest Rate Cap
Derivative [Line Items]
Payments on non-recourse debt	$ 1,700,000
Loss related to decline in derivative fair value		100,000
Ravenhall, Australia | Other Noncurrent Liabilities
Derivative [Line Items]
Fair value of the swap liability					$ 23,600,000
Ravenhall, Australia | Other Noncurrent Assets | Interest Rate Cap
Derivative [Line Items]
Interest rate swap asset value					$ 100,000
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 362.8	$ 278,200,000
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 466.3	$ 357,600,000
Ravenhall, Australia | Cash Flow Hedge
Derivative [Line Items]
Unrealized losses, net of tax, related to cash flow hedge		$ 2,500,000
Construction Facility | Non-Recourse Debt | National Australia Bank Limited | Ravenhall
Derivative [Line Items]
Lump sum due at completion				AUD 310.0	$ 237,700,000