Derivative Instruments - Oil and Natural-Gas Production/Processing Derivative Activities Table (Detail) - Jun. 30, 2015 - Not Designated as Hedging Instrument [Member] - Price Risk Derivative [Member]		MMBTU / d MBbls / d $ / bbl $ / MMBTU
Three-Way Collars Natural Gas 2015 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day | MMBTU / d		635,000
Three-Way Collars Natural Gas 2015 [Member] | Call Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average ceiling price		4.76
Three-Way Collars Natural Gas 2015 [Member] | Put Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average floor price		2.75
Three-Way Collars Natural Gas 2015 [Member] | Put Option [Member] | Long [Member]
Average price per MMBtu or barrel
Average floor price		3.75
Forward Contracts Natural Gas 2015 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day | MMBTU / d		7,000
Average price per MMBtu or barrel
Average price per MMBtu or barrel		2.56
Forward Contracts Natural Gas 2016 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day | MMBTU / d		28,000
Average price per MMBtu or barrel
Average price per MMBtu or barrel		3.22
Extendable Fixed Price Contracts Natural Gas 2015 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day | MMBTU / d	[1]	170,000
Average price per MMBtu or barrel
Average price per MMBtu or barrel		4.17
Three Way Collars Oil 2016 [Member]
Derivative [Line Items]
Oil derivative nonmonetary notional amount per day | MBbls / d		28
Three Way Collars Oil 2016 [Member] | Call Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average ceiling price | $ / bbl		69.29
Three Way Collars Oil 2016 [Member] | Put Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average floor price | $ / bbl		46.43
Three Way Collars Oil 2016 [Member] | Put Option [Member] | Long [Member]
Average price per MMBtu or barrel
Average floor price | $ / bbl		61.43

[1] The extendable fixed-price contracts have a contract term of January 2015 to December 2015 with an option for the counterparty to extend the contract term to December 2016 at the same price.