Derivative Instruments and Hedging Activities - Hedging Positions (Detail)	Mar. 31, 2015 MBbls
Oil (MBbls) [Member] | 2015 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	89.00
Oil (MBbls) [Member] | 2015 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	90.00
Oil (MBbls) [Member] | 2015 Hedging Position Three [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	90.25
Oil (MBbls) [Member] | 2015 Hedging Position Four [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	90.40
Oil (MBbls) [Member] | 2015 Hedging Position Five [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	91.05
Oil (MBbls) [Member] | 2015 Hedging Position Six [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	93.28
Oil (MBbls) [Member] | 2015 Hedging Position Seven [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	93.37
Oil (MBbls) [Member] | 2015 Hedging Position Eight [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	94.85
Oil (MBbls) [Member] | 2015 Hedging Position Nine [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	95.00
Oil (MBbls) [Member] | 2016 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price	90.00
Natural Gas (MMcfe) [Member] | 2015 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.005
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.120
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Three [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.150
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Four [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.165
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Five [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.220
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Six [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.255
Natural Gas (MMcfe) [Member] | 2016 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.110
Natural Gas (MMcfe) [Member] | 2016 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	10,000
Swap Price	4.120