Derivative Activities - Effects of Non-Hedge Derivatives on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Financial Instruments [Line Items]
Derivative Fair Value Income (Loss)	$ (34,791)	$ (24,109)	$ 88,048	$ (170,959)
Swaps
Derivative Financial Instruments [Line Items]
Derivative Fair Value Income (Loss)	(42,100)	(38,521)	83,676	(82,593)
Collars
Derivative Financial Instruments [Line Items]
Derivative Fair Value Income (Loss)	(1,650)	1,032	6,765	(38,116)
Basis Swaps
Derivative Financial Instruments [Line Items]
Derivative Fair Value Income (Loss)	$ 8,959	$ 13,380	$ (2,393)	$ (50,250)