Derivative Instruments - Oil and Natural-Gas Production/Processing Derivative Activities Table (Detail) - Not Designated as Hedging Instrument [Member] - Price Risk Derivative [Member] MMBTU / d in Thousands	12 Months Ended
	Dec. 31, 2015 MMBTU / d MBbls / d $ / bbl $ / MMBTU
Three Way Collars Oil 2016 [Member]
Derivative [Line Items]
Oil derivative nonmonetary notional amount per day | MBbls / d	83
Three Way Collars Oil 2016 [Member] | Call Option [Member] | Short [Member]
Average price per barrel
Average ceiling price	63.82
Three Way Collars Oil 2016 [Member] | Put Option [Member] | Short [Member]
Average price per barrel
Average floor price	42.77
Three Way Collars Oil 2016 [Member] | Put Option [Member] | Long [Member]
Average price per barrel
Average floor price	54.46
Forward Contracts Natural Gas 2016 [Member]
Derivative [Line Items]
Natural-gas derivative nonmonetary notional amount per day | MMBTU / d	38
Average price per MMBtu or barrel | $ / MMBTU	2.53
Forward Contracts Natural Gas Liquids 2016 [Member]
Derivative [Line Items]
Oil derivative nonmonetary notional amount per day | MBbls / d	4
Average price per MMBtu or barrel	13.07