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Asset Retirement Obligations (Schedule Of Change In Asset Retirement Obligation) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Asset Retirement Obligations [Abstract]
Asset retirement obligations, Beginning balance	$ 126,991
Asset retirement obligations, Liabilities settled	(820)
Asset retirement obligations, Accretion expense	1,732	1,322
Asset retirement obligations, Ending balance	127,903
Less: Current portion of asset retirement obligations	(903)		(1,426)
Asset retirement obligations - non-current	$ 127,000		$ 125,565

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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