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Asset Retirement Obligations (Schedule Of Changes In Asset Retirement Obligation) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Asset Retirement Obligations [Abstract]
Asset retirement obligation at beginning of year	$ 3,887	$ 3,971	$ 4,208
New liability recognized		19
Liability settled	(612)	(460)	(499)
Accretion expense	238	357	262
Asset retirement obligation at end of year	$ 3,513	$ 3,887	$ 3,971

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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