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Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 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 369,000 356,000
Oil/Natural Gas Derivative Liabilities, Notional Amount 1,363,000 1,574,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value $ 553 $ 1,004
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value (3,757) (2,704)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
    
Derivative Instruments [Line Items]    
Oil/Natural Gas Derivative Assets, Notional Amount 8,920,000 14,240,000
Oil/Natural Gas Derivative Liabilities, Notional Amount 31,390,000 22,510,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value 2,627 2,903
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value (5,868) (3,212)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
    
Derivative Instruments [Line Items]    
Oil/Natural Gas Derivative Assets, Notional Amount 1,363,000 1,574,000
Oil/Natural Gas Derivative Liabilities, Notional Amount 369,000 356,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value 3,863 2,818
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value (549) (991)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
    
Derivative Instruments [Line Items]    
Oil/Natural Gas Derivative Assets, Notional Amount 31,390,000 22,850,000
Oil/Natural Gas Derivative Liabilities, Notional Amount 8,920,000 13,900,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value 6,076 3,301
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value $ (2,623) $ (2,805)