Fair Value Measurements - Additional Information (Detail) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 Barnett Shale properties [Member]	Dec. 31, 2012 Surface property [Member]	Dec. 31, 2012 Mississippi [Member]	Dec. 31, 2012 North Central Texas [Member]	Sep. 30, 2011 East Texas [Member]	Dec. 31, 2011 East Texas [Member]	Dec. 31, 2011 Gulf Coast [Member]	Dec. 31, 2010 Gulf Coast [Member]	Dec. 31, 2010 Discontinued operations [Member]	Dec. 31, 2010 Discontinued operations [Member] Barnett Shale [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Interest and dividends	$ 1,400,000	$ 1,400,000	$ 864,000
Mark-to-market gain (loss)	4,700,000	2,300,000	11,500,000
Impairment on oil and gas properties	34,273,000	38,681,000	6,505,000	463,200,000		31,100,000	3,200,000	31,200,000	31,200,000	7,500,000	6,500,000	463,244,000
Impairment charge related to discontinued operations													463,200,000
Impairment of long lived assets					$ 1,281,000