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Asset Retirement Obligations (Details) (USD $) In Thousands	6 Months Ended
Asset Retirement Obligations (Details) (USD $) In Thousands	Jun. 30, 2011
Asset Retirement Obligations
Beginning of period - continuing operations	$ 60,693
Liabilities incurred	1,447
Liabilities settled	(1,625)
Accretion expense - continuing operations	2,580
Change in estimate	11,270
End of period - continuing operations	$ 74,365

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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