Derivative Instruments - Realized and Unrealized Gains and Losses on Derivative Instruments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Cash received (paid) on derivatives:
Cash received (paid) on derivatives, net	$ 13,182	$ (64,143)	$ 36,617	$ (97,407)
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	(17,919)	(198,381)	(8,599)	(204,791)
Gain (loss) on derivative instruments, net	(4,737)	(262,524)	28,018	(302,198)
Fixed price swaps | Crude Oil [Member]
Cash received (paid) on derivatives:
Cash received (paid) on derivatives, net	0	(50,499)	0	(73,022)
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	0	(201,482)	0	(187,792)
Fixed price swaps | Natural Gas [Member]
Cash received (paid) on derivatives:
Cash received (paid) on derivatives, net	5,551	(12,191)	23,942	(22,348)
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	(9,296)	7,494	(2,804)	(17,907)
Collars | Crude Oil [Member]
Cash received (paid) on derivatives:
Cash received (paid) on derivatives, net	0	(1,453)	0	(2,037)
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	0	(4,369)	0	914
Collars | Natural Gas [Member]
Cash received (paid) on derivatives:
Cash received (paid) on derivatives, net	7,631	0	12,675	0
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	(8,626)	(24)	(9,722)	(6)
Call Option [Member] | Crude Oil [Member]
Non-cash gain (loss) on derivatives:
Non-cash gain (loss) on derivatives, net	$ 3	$ 0	$ 3,927	$ 0