Equity Investments and Membership Interests in Joint Ventures (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended		12 Months Ended						12 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2013 Knight Hawk [Member]	Sep. 30, 2013 DKRW [Member]	Dec. 31, 2013 DKRW [Member]	Dec. 31, 2012 DKRW [Member]	Dec. 31, 2013 DTA [Member]	Dec. 31, 2013 Tenaska [Member]	Dec. 31, 2011 Tenaska [Member]	Dec. 31, 2013 Millennium [Member]	Dec. 31, 2011 Millennium [Member]	Jan. 31, 2011 Millennium [Member]	Dec. 31, 2013 Tongue River [Member]	Dec. 31, 2011 Tongue River [Member]	Jul. 31, 2011 Tongue River [Member]	Dec. 31, 2013 Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage				49.00%		24.00%		21.875%	35.00%				38.00%			35.00%
Due from Related Parties							$ 38,700,000
Other than Temporary Impairment Losses, Investments						(57,700,000)			(20,500,000)
Impairment of equity investment		(28,947,000)			(13,683,000)				(15,264,000)
Provision for Loan, Lease, and Other Losses	(5,200,000)				(44,000,000)
Investments in affiliates			43,489,000							5,500,000		25,000,000			12,989,000
Future development costs, maximum limit																	$ 58,500,000