Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2013

Asset Retirement Obligation [Abstract]

Schedule of asset retirement obligations

The following table summarizes the Company's asset retirement obligation activity during the three months ended March 31, 2013 and 2012:

		Three Months Ended March 31,
		2013			2012
	(in thousands)
Beginning asset retirement obligations		$	197,754		$	136,742
New wells placed on production		2,468			830
Changes in estimates (a)		(5,597		)	—
Dispositions		(4,079		)	—
Liabilities settled		(2,849		)	(5,688		)
Accretion of discount		3,153			2,430
Accretion of discount from integrated services (b)		11			—
Ending asset retirement obligations		$	190,861		$	134,314

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(a) The change in estimate during the three months ended March 31, 2013 is attributable to lengthening the economic life of certain wells, which reduced the present value of the associated asset retirement obligation.

(b) Accretion of discount from integrated services includes Premier Silica accretion expense, which is recorded as a reduction in third-party income from vertical integration services in interest and other income in the Company's accompanying consolidated statements of operations. See Note K for more information about interest and other income.