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Decommissioning and Other Asset Retirement Obligations (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Decommissioning and Other Asset Retirement Obligations Detail [Table]
Beginning balance for the period, as reported	$ 139,835,000	$ 272,815,000
Activity in the period:
Accretion of liability	520,000	1,894,000
Revisions in estimated cash flows	2,233,000	9,764,000
Settlement of retirement obligations	(15,744,000)	(53,639,000)
Ending balance at March 31	126,844,000	230,834,000
Amount of asset retirement obligations assumed by buyers of oil and gas properties	$ 46,000,000

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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