Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 97,956	$ 128,981
Derivative assets, noncurrent	0	35,897
Derivative assets	97,956	164,878
Derivative liabilities	0	0
Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative assets	98,000
Commodity contracts \| Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Derivative assets, current	97,956	128,981
Derivative liabilities, current	0	0
Commodity contracts \| Derivative assets/liabilities - noncurrent
Derivatives, Fair Value [Line Items]
Derivative assets, noncurrent	0	35,897
Derivative liabilities, noncurrent	$ 0	$ 0

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