Equity Investments And Membership Interests In Joint Ventures (Schedule Of Equity Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	$ 225,605
Investments in affiliates
Advances to (distributions from) affiliates, net	5,449
Equity in comprehensive income (loss)	6,591
Balance at September 30, 2012	237,645
Notes receivable from investees: Balance at December 31, 2011	41,478	35,810
Notes receivable from investees: Balance at September 30, 2012	41,478	35,810
Knight Hawk [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	135,225
Investments in affiliates
Advances to (distributions from) affiliates, net	(5,342)
Equity in comprehensive income (loss)	16,033
Balance at September 30, 2012	145,916
Notes receivable from investees: Balance at December 31, 2011
Notes receivable from investees: Balance at September 30, 2012
DKRW [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	19,715
Investments in affiliates
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)	(3,457)
Balance at September 30, 2012	16,258
Notes receivable from investees: Balance at December 31, 2011	36,402	30,751
Notes receivable from investees: Balance at September 30, 2012	36,402	30,751
DTA [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	16,086
Investments in affiliates
Advances to (distributions from) affiliates, net	3,230
Equity in comprehensive income (loss)	(3,625)
Balance at September 30, 2012	15,691
Notes receivable from investees: Balance at December 31, 2011
Notes receivable from investees: Balance at September 30, 2012
Tenaska [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	15,266
Investments in affiliates
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)	(2)
Balance at September 30, 2012	15,264
Notes receivable from investees: Balance at December 31, 2011	5,076	5,059
Notes receivable from investees: Balance at September 30, 2012	5,076	5,059
Millennium [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	26,324
Investments in affiliates
Advances to (distributions from) affiliates, net	5,853
Equity in comprehensive income (loss)	(2,358)
Balance at September 30, 2012	29,819
Notes receivable from investees: Balance at December 31, 2011
Notes receivable from investees: Balance at September 30, 2012
Tongue River [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Balance at December 31, 2011	12,989
Investments in affiliates
Advances to (distributions from) affiliates, net	1,708
Equity in comprehensive income (loss)
Balance at September 30, 2012	14,697
Notes receivable from investees: Balance at December 31, 2011
Notes receivable from investees: Balance at September 30, 2012