Derivative Financial Instruments - Australia Ravenhall (Details)	12 Months Ended									12 Months Ended			12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2014 Interest Rate Swap Asset under Construction Ravenhall, Australia USD ($)	Dec. 31, 2014 Interest Rate Swap Asset under Construction Ravenhall, Australia AUD	Sep. 30, 2014 Interest Rate Swap Asset under Construction Ravenhall, Australia	Dec. 31, 2014 Interest Rate Swap Operating Phase of Asset Ravenhall, Australia USD ($)	Dec. 31, 2014 Interest Rate Swap Operating Phase of Asset Ravenhall, Australia AUD	Sep. 30, 2014 Interest Rate Swap Operating Phase of Asset Ravenhall, Australia	Dec. 31, 2014 Interest Rate Cap Ravenhall, Australia USD ($)	Dec. 31, 2014 National Australia Bank Limited Non Recourse Debt Ravenhall USD ($)	Dec. 31, 2014 National Australia Bank Limited Non Recourse Debt Ravenhall AUD	Dec. 31, 2014 Cash Flow Hedging Ravenhall, Australia USD ($)	Dec. 31, 2014 Other Noncurrent Liabilities Ravenhall, Australia USD ($)	Dec. 31, 2014 Other Noncurrent Assets Interest Rate Cap Ravenhall, Australia USD ($)
Derivative [Line Items]
Fixed interest rate on cash flow interest rate derivative						3.30%			4.20%
Notional amount				$ 79,400,000	97,400,000		$ 380,400,000	466,300,000
Change in fair value of derivative instrument classified as cash flow hedge	(16,048,000)	183,000	(476,000)										(16,100,000)
Value of swap liability														19,000,000
Lump sum due at completion											252,900,000	310,000,000
Payments on non-recourse debt	18,627,000	0	0							1,700,000
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments										(1,200,000)
Interest rate fair value hedge asset at fair value															$ 600,000