Summary of Impairment Charges (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Impaired Long-Lived Assets Held and Used [Line Items]
Oil and gas properties	$ 34,000	$ 71,000	$ 9,700	$ 35,100	$ 104,688	$ 43,067	$ 102,332
Other - tubular inventory and well materials						2,892	4,083
Impairments					$ 104,688	$ 45,959	$ 106,415