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Oil And Gas Properties (Changes In Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligation [Abstract]
Asset retirement obligations at January 1,	$ 227,090	$ 222,653
Liability incurred during the period	3,664	4,982
Liability settled during the period	(105,160)	(37,769)
Other revisions in estimated cash flows	62,834	22,345
Accretion expense (included in depreciation and amortization)	12,550	14,879
Asset retirement obligations at December 31,	$ 200,978	$ 227,090

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

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