Derivative Instruments - Summary of Outstanding Contracts with Respect to Crude Oil (Detail)	12 Months Ended
	Dec. 31, 2014 bbl
ICE Brent [Member] | Call Option July 2015 to December 2015 [Member]
Derivative [Line Items]
Volume (Bbls)	368,000
Derivative, Average Price Risk Option Strike Price	107.4
ICE Brent [Member] | Call Option January 2016 to December 2016 [Member]
Derivative [Line Items]
Volume (Bbls)	1,464,000
Derivative, Average Price Risk Option Strike Price	107.7
Nymex West Texas Intermediate [Member] | Call Option July 2015 to December 2015 [Member]
Derivative [Line Items]
Volume (Bbls)	2,208,000
Derivative, Average Price Risk Option Strike Price	98.36
Nymex West Texas Intermediate [Member] | Minimum [Member] | Call Option July 2015 to December 2015 [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	95.85
Nymex West Texas Intermediate [Member] | Maximum [Member] | Call Option July 2015 to December 2015 [Member]
Derivative [Line Items]
Derivative, Price Risk Option Strike Price	103.75