Segment Information (Reconciliation Of Total Segment Margin To Net Income (Loss) From Continuing Operations Before Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Segment Reporting Information [Line Items]
Total segment margin	$ 107,001	$ 110,741	$ 350,408		$ 308,755
Operation and maintenance	(41,275)	(37,950)	(121,248)		(105,506)
General and administrative, including related party	(14,935)	(17,350)	(47,106)		(54,010)
(Gain) loss on asset sales, net	42	131	(1,542)		(50)
Depreciation and amortization	(45,881)	(41,956)	(142,519)		(122,695)
Income from unconsolidated affiliates	21,055	30,946	87,198		86,921
Interest expense, net	(28,567)	(28,852)	(86,058)		(73,548)
Loss on debt refinancing, net	0	0	(7,820)		0
Other income and deductions, net	1,106	15,050	25,549	[1]	20,105
Income (loss) before income taxes	(1,454)	30,760	56,862		59,972
Customer Contracts [Member]
Segment Reporting Information [Line Items]
Other income and deductions, net			$ 15,600

[1] Other income and deductions, net for the nine months ended September 30, 2012, included a one-time producer payment of $15.6 million related to an assignment of certain contracts.