Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	0 Months Ended	12 Months Ended	1 Months Ended	4 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Aug. 31, 2014 Contract	Dec. 31, 2014 Contract	Dec. 31, 2015 Contract	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Maximum correlation between price of oil & natural gas in market and underlying price basis indicative in the derivative contract	100.00%	100.00%		100.00%
Accumulated other comprehensive income	$ 83,315	$ 83,315		83,315		$ (2,062)	$ 28,833
Accumulated other comprehensive income, to be reclassified into earnings in the next twelve months		77,991
Fair Value of Derivative Instruments, Assets Effect of Netting	0
Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive income	$ 86,783	$ 86,783		86,783		$ (1,395)	$ 28,833	$ 21,868
Natural Gas (MMcfe) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of Contracts no longer qualifying as cash flow hedges			3	4
Scenario, Forecast [Member] | Natural Gas (MMcfe) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Number of Contracts no longer qualifying as cash flow hedges					3