XML 17 R37.htm IDEA: XBRL DOCUMENT

ASSET RETIREMENT OBLIGATIONS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Disclosure Changes In Aggregate Asset Retirement Obligation [Abstract]
Balance at beginning of period	$ 104,684	$ 93,225
Liabilities incurred	320	375
Accretion expense	1,354	1,208
Revisions in estimated cash flows		1,056
Settlements and divestitures	(278)	(112)
Balance at end of period	106,080	95,752
Asset retirement obligation, current	$ 1,977		$ 1,977

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.

+ References+ Details

- 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.

+ References+ Details