Derivative Instruments and Hedging Activities - Hedging Positions (Detail) - Aug. 05, 2015 - Subsequent Event [Member]	MMBTU MBbls $ / MMBTU $ / bbl
Oil (MBbls) [Member] | 2015 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	89.00
Oil (MBbls) [Member] | 2015 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	90.00
Oil (MBbls) [Member] | 2015 Hedging Position Three [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	90.25
Oil (MBbls) [Member] | 2015 Hedging Position Four [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	90.40
Oil (MBbls) [Member] | 2015 Hedging Position Five [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	91.05
Oil (MBbls) [Member] | 2015 Hedging Position Six [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	93.28
Oil (MBbls) [Member] | 2015 Hedging Position Seven [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	93.37
Oil (MBbls) [Member] | 2015 Hedging Position Eight [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	94.85
Oil (MBbls) [Member] | 2015 Hedging Position Nine [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	95.00
Oil (MBbls) [Member] | 2016 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume	1,000
Swap Price | $ / bbl	90.00
Natural Gas (MMcfe) [Member] | 2015 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.005
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.120
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Three [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.150
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Four [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.165
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Five [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.220
Natural Gas (MMcfe) [Member] | 2015 Hedging Position Six [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.255
Natural Gas (MMcfe) [Member] | 2016 Hedging Position One [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.110
Natural Gas (MMcfe) [Member] | 2016 Hedging Position Two [Member]
Derivatives, Fair Value [Line Items]
Daily Volume | MMBTU	10,000
Swap Price | $ / MMBTU	4.120