Asset Retirement Obligation (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012
Asset Retirement Obligation [Abstract]
Balance	$ 2,099
Accretion expense	70	67
Liabilities incurred	3
Liabilities settled	(12)	(41)
Balance	$ 2,160

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

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