Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2012

Asset Retirement Obligation Disclosure [Abstract]

Reconciliation of Asset Retirement Obligations which are Included in Other Liabilities

The following table reconciles our AROs as of the dates presented, which are included in the Other liabilities caption on our Consolidated Balance Sheets: 

	As of December 31,
	2012			2011
Balance at beginning of year	$	6,283		$	7,364
Liabilities incurred	57			214
Liabilities settled	(236		)	(183		)
Sale of properties	(1,976		)	(1,611		)
Accretion expense	385			499
Balance at end of year	$	4,513		$	6,283