Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2011

Asset Retirement Obligation

Components of Asset Retirement Obligation

	2011	2010
	(in thousands)
Asset retirement obligation at January 1	$        27,786	$        22,972
Accretion of discount	1,361	1,095
Obligations incurred	4,304	6,926
Obligations settled/removed	(883)	(477)
Revisions of estimates	5,125	(2,730)
Asset retirement obligation at December 31	$        37,693	$        27,786
Current liability	1,539	1,829
Long-term liability	36,154	25,957
Asset retirement obligation at December 31	$        37,693	$        27,786