Derivative Instruments - Summary of Outstanding Contracts with Respect to Crude Oil (Detail)	6 Months Ended
	Jun. 30, 2013 bbl
West Texas Intermediate [Member] | July 2013 - December 2013
Derivative [Line Items]
Volume (Bbls)	5,796,000
Swaps Weighted Average Price	92.65
West Texas Intermediate [Member] | Collars
Derivative [Line Items]
Volume (Bbls)	4,416,000
Floors, Weighted Average Price	86.92
Ceilings, Weighted Average Price	99.46
West Texas Intermediate [Member] | January 2014 - December 2014
Derivative [Line Items]
Volume (Bbls)	10,311,250
Swaps Weighted Average Price	96.20
West Texas Intermediate [Member] | Minimum [Member] | Collars
Derivative [Line Items]
Floors, Range	80.00
Ceilings, Range	92.30
West Texas Intermediate [Member] | Maximum [Member] | Collars
Derivative [Line Items]
Floors, Range	95.00
Ceilings, Range	110.33
ICE Brent [Member] | July 2013 - December 2013
Derivative [Line Items]
Volume (Bbls)	2,484,000
Swaps Weighted Average Price	108.72
ICE Brent [Member] | Collars
Derivative [Line Items]
Volume (Bbls)	2,190,000
Floors, Weighted Average Price	90.83
Ceilings, Weighted Average Price	107.13
ICE Brent [Member] | January 2014 - December 2014
Derivative [Line Items]
Volume (Bbls)	13,687,500
Swaps Weighted Average Price	102.52
ICE Brent [Member] | January 2015 - December 2015
Derivative [Line Items]
Volume (Bbls)	1,277,500
Swaps Weighted Average Price	98.48
ICE Brent [Member] | Minimum [Member] | Collars
Derivative [Line Items]
Floors, Range	90.00
Ceilings, Range	104.70
ICE Brent [Member] | Maximum [Member] | Collars
Derivative [Line Items]
Floors, Range	95.00
Ceilings, Range	108.85