Asset Retirement Obligations Reconciliation of Asset Retirement Obligation Liability (Tables)

12 Months Ended

Dec. 31, 2011

Reconciliation of Asset Retirement Obligation Liability [Abstract]

Schedule of Change in Asset Retirement Obligation [Table Text Block]

A reconciliation of the Company’s asset retirement obligation liability is as follows:

	As of December 31,
	2011			2010
	(in thousands)
Beginning asset retirement obligation	$	82,849		$	102,080
Liabilities incurred	5,465			4,738
Liabilities settled	(8,365		)	(30,523		)
Accretion expense	5,948			5,583
Revision to estimated cash flows	10,009			971
Ending asset retirement obligation	$	95,906		$	82,849