Derivative Instruments - Oil and Natural-Gas Production/Processing Derivative Activities Table (Detail) (Not Designated as Hedging Instrument [Member], Price Risk Derivative [Member])	9 Months Ended
	Sep. 30, 2014
Three-Way Collars Natural Gas 2014 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day	600,000
Three-Way Collars Natural Gas 2014 [Member] | Call Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average ceiling price	5.01
Three-Way Collars Natural Gas 2014 [Member] | Put Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average floor price	2.75
Three-Way Collars Natural Gas 2014 [Member] | Put Option [Member] | Long [Member]
Average price per MMBtu or barrel
Average floor price	3.75
Three-Way Collars Natural Gas 2015 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day	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
Fixed-Price Contracts Natural Gas 2014 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day	1,000,000
Average price per MMBtu or barrel
Average price per MMBtu or barrel	4.23
Three-Way Collars Crude Oil 2015 [Member]
Derivative [Line Items]
Crude-oil derivative nonmonetary notional amount per day	25
Three-Way Collars Crude Oil 2015 [Member] | Call Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average ceiling price	117.55
Three-Way Collars Crude Oil 2015 [Member] | Put Option [Member] | Short [Member]
Average price per MMBtu or barrel
Average floor price	85.00
Three-Way Collars Crude Oil 2015 [Member] | Put Option [Member] | Long [Member]
Average price per MMBtu or barrel
Average floor price	100.00
Fixed-Price Contracts Crude Oil 2014 [Member]
Derivative [Line Items]
Crude-oil derivative nonmonetary notional amount per day	140
Average price per MMBtu or barrel
Average price per MMBtu or barrel	101.94