Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 bbl	Dec. 31, 2013 bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	664,000	356,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	402,000	1,574,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 2,228	$ 1,004
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(339)	(2,704)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	14,410,000	14,240,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	16,740,000	22,510,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	3,893	2,903
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(2,236)	(3,212)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	402,000	1,574,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	664,000	356,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	349	2,818
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(2,174)	(991)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	16,800,000	22,850,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	14,350,000	13,900,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	2,250	3,301
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (3,800)	$ (2,805)