Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 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	281,000	356,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	1,130,000	1,574,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 188	$ 1,004
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(6,523)	(2,704)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	8,540,000	14,240,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	27,630,000	22,510,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	2,126	2,903
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(4,527)	(3,212)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	1,130,000	1,574,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	281,000	356,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	6,608	2,818
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	(188)	(991)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount	27,630,000	22,850,000
Oil/Natural Gas Derivative Liabilities, Notional Amount	8,540,000	13,900,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	4,688	3,301
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (2,124)	$ (2,805)