Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Company Lenders	Sep. 30, 2012	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and dividends	$ 111,000	$ 122,000	$ 779,000	$ 279,000
Mark-to-market gain (loss)	3,200,000	3,800,000	3,800,000	5,700,000
Allowance for uncollectible receivables	2,500,000		2,500,000		2,400,000
Number of financial institutions included in counter parties			15
Number of secured lenders not in banking credit facility			2
Net derivative asset	53,000		53,000
Impairment of proved properties and other assets	7,012,000	1,281,000	7,753,000	1,281,000
Surface Property | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment of proved properties and other assets		1,281,000	741,000	1,281,000
Natural Gas and Oil Properties | Fair Value, Measurements, Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment of proved properties and other assets	$ 7,012,000		$ 7,012,000