Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended				12 Months Ended
	Dec. 31, 2014	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and dividends					$ 911,000	$ 1,200,000	$ 1,400,000
Mark-to-market gain (loss)					(2,400,000)	3,900,000	4,700,000
Impairment	3,033,000	24,991,000	7,012,000	741,000	28,024,000	7,753,000	35,554,000
Mississippi
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties					5,500,000		31,100,000
West Texas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties					18,500,000
North Texas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties					4,000,000		3,200,000
Gulf Coast
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment on natural gas and oil properties						7,000,000
Surface Property | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment						$ 741,000	$ 1,281,000
Basis Swaps | Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of natural gas basis swap	0				0	4