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Decommissioning and Other Asset Retirement Obligations (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Decommissioning and Other Asset Retirement Obligations Detail [Table]
Beginning balance for the period, as reported	$ 57,330,000	$ 94,921,000
Activity in the period:
Accretion of liability	173,000	504,000
Revisions in estimated cash flows	21,538,000	54,404,000
Settlement of retirement obligations	(33,738,000)	(104,526,000)
Ending balance as of June 30	45,303,000	45,303,000
Fair value of asset retirement obligations associated with non-operated properties	8,000,000	8,000,000	7,500,000
Asset retirement obligations associated with properties sold during the period		$ 5,300,000

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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