Oil And Gas Properties (Changes In Asset Retirement Obligations) (Details) (USD $) In Thousands	9 Months Ended
Sep. 30, 2011
Oil And Gas Properties
Asset retirement obligations at December 31, 2010	$ 234,936
Liability incurred during the period	1,372
Liability settled during the period	(36,591)
Revision in estimated cash flows	22,276
Accretion expense (included in depreciation and amortization)	11,252
Asset retirement obligations at September 30, 2011	$ 233,245

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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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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Amount of asset retirement obligations incurred during the period.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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