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

12 Months Ended

Dec. 31, 2012

Asset Retirement Obligation [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,
	2012			2011
	(in thousands)
Beginning asset retirement obligation	$	95,906		$	82,849
Liabilities incurred	13,050			5,465
Liabilities settled	(8,101		)	(8,365		)
Accretion expense	4,679			5,948
Revision to estimated cash flows	14,984			10,009
Ending asset retirement obligation	$	120,518		$	95,906