Asset Retirement Obligations

12 Months Ended

Dec. 31, 2012

Asset Retirement Obligations [Abstract]

Asset Retirement Obligations

(6) Asset Retirement Obligations

We record the fair value of a liability for an asset retirement obligation in the period in which it is incurred, along with a corresponding increase in the carrying amount of the related long-lived asset. The following table reconciles the beginning and ending aggregate recorded amount of our asset retirement obligations.

		Year Ended December 31,
		2012		2011
		(in thousands)
Beginning of period total	$	99,347	$	71,583
Accretion expense		15,565		15,942
Liabilities assumed in acquisitions		132,109		26,435
Liabilities incurred		1,210		157
Revisions		22,308		17,595
Liabilities settled		(35,429)		(32,365)
End of period total		235,110		99,347
Less: End of period, current portion		(30,179)		(25,578)
End of period, noncurrent portion	$	204,931	$	73,769

As of December 31, 2011, we increased our cost estimates on a portion of our asset retirement obligations to reflect higher overall prices for services, material and equipment. Primarily due to changes in estimated reserve lives, the timing of a portion of our asset retirement obligations was revised in the fourth quarter of 2011 leading to a reduction of the present value of those obligations, partially offsetting the impact of the cost increases.