Asset Retirement Obligations (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Asset Retirement Obligation [Abstract]
Beginning asset retirement obligations	$ 134,314,000		$ 154,689,000		$ 136,742,000		$ 152,291,000
Liabilities assumed in acquisitions	8,515,000		0		8,515,000		6,000
New wells placed on production	1,581,000		1,404,000		2,411,000		2,075,000
Changes in estimates	1,603,000		(179,000)		1,603,000		121,000
Disposition of wells	0		367,000		0		448,000
Liabilities settled	3,054,000		6,235,000		8,742,000		7,469,000
Accretion of discount from continuing operations	2,444,000		2,048,000		4,874,000		4,092,000
Accretion of discount from integrated services	54,000	[1]	0	[1]	54,000	[1]	0	[1]
Accretion of discount from discontinued operations	0		610,000		0		1,302,000
Ending asset retirement obligations	145,457,000		151,970,000		145,457,000		151,970,000
Asset retirement obligations, current portions	$ 18,600,000				$ 18,600,000				$ 14,200,000

[1] 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 M for more information about interest and other income.