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ASSET RETIREMENT OBLIGATION (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Asset Retirement Obligation
Balance at the beginning of the period	$ 67,016
Liabilities incurred	1,396
Liabilities settled	(195)
Accretion expense	876
Balance at the end of the period	$ 69,093

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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