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
	Mar. 31, 2012		Mar. 31, 2011
Segment Reporting Information [Line Items]
Total segment margin	$ 118,246		$ 100,991
Operation and maintenance	(40,981)		(33,672)
General and administrative, including related party	(15,695)		(18,997)
Loss on asset sales, net	36		28
Depreciation and amortization	(51,506)		(40,236)
Income (Loss) from Equity Method Investments	31,958		23,808
Interest Expense	(29,557)		(20,007)
Other income and deductions, net	16,522	[1]	2,414
Income (Loss) from Continuing Operations before Income Taxes	28,951		14,273
Customer Contracts [Member]
Segment Reporting Information [Line Items]
Other income and deductions, net	$ 15,600

[1] *Other income and deductions, net for the three months ended March 31, 2012 included a one-time producer payment of $15.6 million related to an assignment of certain contracts.