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Asset Retirement Obligations (Schedule Of Reconciliation Of Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Asset Retirement Obligations [Abstract]
Asset retirement obligations at January 1, 2012	$ 58,088
Liabilities incurred during the period	264
Liabilities settled during the period	(165)
Accretion of discount	947	857
Asset retirement obligations at March 31, 2012	59,134
Less current portion	732		732
Long-term portion	$ 58,402

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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