Equity Investments And Membership Interests In Joint Ventures (Schedule Of Equity Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	$ 242,215
Advances to (distributions from) affiliates, net	3,384
Equity in comprehensive income (loss)	1,208
Ending Balance	246,807
Notes receivable from investees	46,216	43,828
Knight Hawk [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	149,063
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)	4,515
Ending Balance	153,578
Notes receivable from investees
DKRW [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	15,515
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)	(733)
Ending Balance	14,782
Notes receivable from investees	41,019	38,680
DTA [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	15,462
Advances to (distributions from) affiliates, net	593
Equity in comprehensive income (loss)	(1,609)
Ending Balance	14,446
Notes receivable from investees
Tenaska [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	15,264
Advances to (distributions from) affiliates, net
Equity in comprehensive income (loss)
Ending Balance	15,264
Notes receivable from investees	5,197	5,148
Millennium [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	32,214
Advances to (distributions from) affiliates, net	1,790
Equity in comprehensive income (loss)	(684)
Ending Balance	33,320
Notes receivable from investees
Tongue River [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance	14,697
Advances to (distributions from) affiliates, net	1,001
Equity in comprehensive income (loss)	(281)
Ending Balance	15,417
Notes receivable from investees