Decommissioning Liabilities (Details) (USD $) In Thousands	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Summary of the activity for the Company's decommissioning liabilities
Decommissioning liabilities, December 31, 2010 and 2009, respectively	$ 117,716	$ 0
Liabilities acquired and incurred	0	136,559
Accretion	5,038	5,361
Revision in estimated liabilities	(292)
Total decommissioning liabilities, September 30, 2011 and 2010, respectively	122,462	141,920
Less: current portion of decommissioning liabilities at September 30, 2011 and 2010, respectively	17,090	25,804	16,929
Long-term decommissioning liabilities, September 30, 2011 and 2010, respectively	$ 105,372	$ 116,116	$ 100,787

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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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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Current portion of 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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Amount of asset retirement obligations incurred during the period.

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Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Noncurrent portion of 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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