Asset Retirement Obligations (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Asset Retirement Obligations [Abstract]
Beginning asset retirement obligations	$ 136,742,000		$ 152,291,000
Liabilities assumed in acquisitions			6,000
New wells placed on production	830,000		671,000
Changes in estimates			300,000
Disposition of wells			(81,000)
Liabilities settled	(5,688,000)		(1,234,000)
Accretion of discount from continuing operations	2,430,000		2,044,000
Accretion of discount from discontinued operations	652,000	[1]	692,000	[1]
Ending asset retirement obligations	134,314,000		154,689,000
Asset retirement obligations, current portions	$ 14,400,000				$ 14,200,000

[1] Represents the significant noncash components of discontinued operations.