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Decommissioning Liabilities (Details) (USD $) In Thousands	6 Months Ended
Decommissioning Liabilities (Details) (USD $) In Thousands	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Summary of the activity for the Company's decommissioning liabilities
Decommissioning liabilities, December 31, 2010 and 2009, respectively	$ 177,716	$ 0
Liabilities acquired and incurred		126,559
Accretion	3,336	3,359
Total decommissioning liabilities, June 30, 2011 and 2010, respectively	121,052	129,918
Less: current portion of decommissioning liabilities at June 30, 2011 and 2010, respectively	17,172	22,232	16,929
Long-term decommissioning liabilities, June 30, 2011 and 2010, respectively	$ 103,880	$ 107,686	$ 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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- 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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