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Commitments And Contingencies (Schedule Of Changes In Asset Retirement Obligations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Commitments And Contingencies [Abstract]
Balance at January 1	$ 41,079	$ 38,779
Accretion expense	2,645	2,464
Liabilities incurred	3,062	495
Liabilities settled	(2,091)	(392)
Revisions in estimated cash flows	(1,462)	(267)
Balance at December 31	$ 43,233	$ 41,079

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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