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Asset Retirement Obligations (Schedule Of Change In Asset Retirement Obligation) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Asset Retirement Obligations [Abstract]
Asset retirement obligations, Beginning balance			$ 65,701
Asset retirement obligations, Assumed in acquisition			4,738
Asset retirement obligations, Divested			(23)
Asset retirement obligations, Revisions to previous estimates			1,223
Asset retirement obligations, Liabilities settled			(909)
Asset retirement obligations, Accretion expense	887	666	1,730	1,314
Asset retirement obligations, Ending balance	72,460		72,460
Less: Current portion of asset retirement obligations	(808)		(808)		(348)
Asset retirement obligations - non-current	$ 71,652		$ 71,652		$ 65,353

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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