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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011
Segment Reporting Information [Line Items]
Total segment margin	$ 125,161	$ 97,023	$ 243,407		$ 198,014
Operation and maintenance	(38,992)	(33,996)	(79,973)		(67,556)
General and administrative, including related party	(16,476)	(17,551)	(32,171)		(36,660)
Loss on asset sales, net	(1,548)	(153)	(1,584)		(181)
Depreciation and amortization	(45,132)	(40,503)	(96,638)		(80,739)
Income from unconsolidated affiliates	34,185	32,167	66,143		55,975
Interest expense, net	(27,934)	(24,689)	(57,491)		(44,696)
Gains (losses) on extinguishment of debt, net	(7,820)	0	(7,820)		0
Other income and deductions, net	7,921	2,641	24,443	[1]	5,055
Income (loss) before income taxes	29,365	14,939	58,316		29,212
Customer Contracts [Member]
Segment Reporting Information [Line Items]
Other income and deductions, net			$ 15,600

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