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Derivative Instruments and Fair Value Measurements - Summary of Fair Value of Open Commodity Derivatives (Detail) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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Unrealized Gain on Commodity Derivatives [Member] | Commodity Derivatives [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivatives not designated as hedging instruments, fair value of assets derivative | $ 6,737 | $ 39,951

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