Equity Investments And Membership Interests In Joint Ventures (Schedule Of Equity Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended												1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2010 Knight Hawk [Member]	Dec. 31, 2011 Knight Hawk [Member]	Dec. 31, 2010 Knight Hawk [Member]	Dec. 31, 2009 Knight Hawk [Member]	Dec. 31, 2011 DKRW [Member]	Dec. 31, 2010 DKRW [Member]	Dec. 31, 2009 DKRW [Member]	Dec. 31, 2011 DTA [Member]	Dec. 31, 2010 DTA [Member]	Dec. 31, 2009 DTA [Member]	Dec. 31, 2011 Tenaska [Member]	Dec. 31, 2010 Tenaska [Member]	Dec. 31, 2009 Tenaska [Member]	Jan. 31, 2011 Millennium [Member]	Dec. 31, 2011 Millennium [Member]	Dec. 31, 2010 Millennium [Member]	Dec. 31, 2009 Millennium [Member]	Dec. 31, 2011 Tongue River [Member]	Dec. 31, 2010 Tongue River [Member]	Dec. 31, 2009 Tongue River [Member]
Schedule of Equity Method Investments [Line Items]
Beginning, Balance	$ 177,451	$ 87,268	$ 87,761		$ 131,250	$ 49,603	$ 48,093	$ 21,961	$ 23,589	$ 25,124	$ 14,472	$ 14,076	$ 14,544	$ 9,768
Investments in affiliates	43,489	87,405		26,600		77,637								5,500	9,768		25,000	25,000			12,989
Advances to (distributions from) affiliates, net	(6,646)	(8,375)	(2,239)		(16,621)	(12,639)	(5,164)				6,498	4,264	2,925					3,477
Equity in comprehensive income (loss)	11,311	11,153	1,746		20,596	16,649	6,674	(2,246)	(1,628)	(1,535)	(4,884)	(3,868)	(3,393)	(2)				(2,153)
Ending, Balance	225,605	177,451	87,268	131,250	135,225	131,250	49,603	19,715	21,961	23,589	16,086	14,472	14,076	15,266	9,768			26,324			12,989
Balance at December 31, 2010	23,900				1,700			18,100						4,100
Balance at December 31, 2011	$ 35,810	$ 23,900		$ 1,700		$ 1,700		$ 30,751	$ 18,100					$ 5,059	$ 4,100