Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Taxes [Abstract]
Depreciation and depletion	$ 336,471	$ 396,355
Original Issue Discount on 2025 and 2032 Notes	13,098	37,067
Equity investments in production facilities	81,082	76,911
Prepaid and other	10,548	14,779
Total deferred tax liabilities	441,199	525,112
Net operating loss carryforward	(36,981)	(34,987)
Asset retirement obligations	(70,085)	(88,279)
Reserves, accrued liabilities and other	(35,229)	(39,995)
Deferred Tax Assets, Gross	(142,295)	(163,261)
Valuation allowance	16,391	14,310
Current deferred tax assets	(43,942)	(41,449)
Deferred tax liabilities	359,237	417,610
Net deferred tax liabilities	$ 315,295	$ 376,161