Fair Value of Derivative Instruments on Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 446	$ 97,956
Derivative assets	446	97,956
Commodity derivative liabilities – current	(3,888)
Derivative Liability, Noncurrent	11,291	0
Derivative Liability	15,179	0
Commodity contracts
Derivatives, Fair Value [Line Items]
Derivative assets	14,700
Commodity contracts \| Derivative assets/liabilities - current
Derivatives, Fair Value [Line Items]
Derivative assets, current	446	97,956
Commodity derivative liabilities – current	(3,888)	0
Commodity contracts \| Noncurrent Derivative Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Noncurrent	0	0
Derivative Liability, Noncurrent	$ 11,291	$ 0

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