Equity Investments And Membership Interests In Joint Ventures (Schedule Of Equity Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	$ 225,605
Investments in affiliates
Advances to (distributions from) affiliates, net	5,866
Equity in comprehensive income (loss)	3,828
Balance at June 30, 2012	235,299
Notes receivable from investees: Balance at December 31, 2011	35,810
Notes receivable from investees: Balance at June 30, 2012	39,864
Knight Hawk [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	135,225
Investments in affiliates
Advances to (distributions from) affiliates, net	(1,801)
Equity in comprehensive income (loss)	9,641
Balance at June 30, 2012	143,065
DKRW [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	19,715
Investments in affiliates
Equity in comprehensive income (loss)	(1,551)
Balance at June 30, 2012	18,164
Notes receivable from investees: Balance at December 31, 2011	30,751
Notes receivable from investees: Balance at June 30, 2012	34,817
DTA [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	16,086
Investments in affiliates
Advances to (distributions from) affiliates, net	2,150
Equity in comprehensive income (loss)	(2,374)
Balance at June 30, 2012	15,862
Tenaska [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	15,266
Investments in affiliates
Balance at June 30, 2012	15,266
Notes receivable from investees: Balance at December 31, 2011	5,059
Notes receivable from investees: Balance at June 30, 2012	5,047
Millennium [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	26,324
Investments in affiliates
Advances to (distributions from) affiliates, net	4,842
Equity in comprehensive income (loss)	(1,888)
Balance at June 30, 2012	29,278
Tongue River [Member]
Schedule of Equity Method Investments [Line Items]
Balance at December 31, 2011	12,989
Investments in affiliates
Advances to (distributions from) affiliates, net	675
Balance at June 30, 2012	$ 13,664