Equity Investments And Membership Interests In Joint Ventures (Schedule Of Equity Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Jun. 30, 2013	Sep. 30, 2013
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		$ 242,215
Advances to (distributions from) affiliates, net		4,845
Equity in comprehensive income (loss)		(5,441)
Impairment of equity investment		(28,947)
Balance at September 30, 2013		223,554
Knight Hawk [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		149,063
Advances to (distributions from) affiliates, net		(5,342)
Equity in comprehensive income (loss)		(13,362)
Impairment of equity investment
Balance at September 30, 2013		157,083
DKRW [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		15,515
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)		1,832
Impairment of equity investment		(13,683)
Balance at September 30, 2013
DTA [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		15,462
Advances to (distributions from) affiliates, net		2,537
Equity in comprehensive income (loss)		3,855
Impairment of equity investment
Balance at September 30, 2013		14,144
Tenaska [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		15,264
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)
Impairment of equity investment	(15,264)
Balance at September 30, 2013
Millennium [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		32,214
Advances to (distributions from) affiliates, net		4,954
Equity in comprehensive income (loss)		1,953
Impairment of equity investment
Balance at September 30, 2013		35,215
Tongue River [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2012		14,697
Advances to (distributions from) affiliates, net		2,696
Equity in comprehensive income (loss)		281
Impairment of equity investment
Balance at September 30, 2013		$ 17,112