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ASSET RETIREMENT OBLIGATION (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
ASSET RETIREMENT OBLIGATION.
Carrying amount of asset retirement obligations at the beginning of the period	$ 60,142
Liabilities incurred	1,731
Liabilities settled	(1,050)
Accretion expense	2,283
Change in estimate	(37)
Carrying amount of asset retirement obligations at the end of the period	$ 63,069

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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