XML 18 R46.htm IDEA: XBRL DOCUMENT

Asset Retirement Obligation (Schedule Of ARO Activity) (Details) (Asset Retirement Obligation Costs [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligation Costs [Member]
Beginning balance	$ 51,295	$ 52,099
Adjustment due to change in estimate of related costs	3,570	(3,174)
Accretion of liability	4,920	5,001
Liabilities settled	(2,936)	(2,631)
Ending balance	$ 56,849	$ 51,295

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