Derivative Financial Instruments - Australia Ravenhall (Details)	3 Months Ended				3 Months Ended						3 Months Ended
	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Mar. 31, 2015 Ravenhall, Australia USD ($)	Mar. 31, 2015 Ravenhall, Australia Interest Rate Swap USD ($)	Mar. 31, 2015 Ravenhall, Australia Interest Rate Cap USD ($)	Mar. 31, 2015 Ravenhall, Australia Other Noncurrent Liabilities USD ($)	Mar. 31, 2015 Ravenhall, Australia Other Noncurrent Assets Interest Rate Cap USD ($)	Mar. 31, 2015 Ravenhall, Australia Design and construction phase Interest Rate Swap USD ($)	Mar. 31, 2015 Ravenhall, Australia Design and construction phase Interest Rate Swap AUD	Mar. 31, 2015 Ravenhall, Australia Operating phase Interest Rate Swap AUD	Mar. 31, 2015 Ravenhall, Australia Cash Flow Hedge USD ($)	Sep. 30, 2014 Construction Facility Non-Recourse Debt National Australia Bank Limited Ravenhall USD ($)	Sep. 30, 2014 Construction Facility Non-Recourse Debt National Australia Bank Limited Ravenhall AUD
Derivative [Line Items]
Fixed interest rate on derivative								3.34%	3.34%	4.21%
Notional amount coincide with the terms of the non-recourse debt				$ 358,600,000				$ 107,700,000	140,000,000	466,300,000
Unrealized losses, net of tax, related to cash flow hedge	(4,080,000)	27,000									4,100,000
Fair value of the swap liability						23,800,000
Ineffective portion of Cash Flow Hedge interest rate swap			0
Lump sum due at completion												238,400,000	310,000,000
Payments on non-recourse debt	1,645,000	1,403,000			1,700,000
Loss related to decline in derivative fair value					200,000
Interest rate swap asset value							$ 300,000