v3.10.0.1

Derivative Instruments and Fair Value Measurements - Summary of Fair Value of Open Commodity Derivatives (Detail) - Commodity Derivatives [Member] - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Derivatives Fair Value [Line Items] |  |
Derivatives not designated as hedging instruments, Derivatives assets, Fair Value | $ 31 | $ 1,398
Derivatives not designated as hedging instruments, Derivatives liabilities, Fair Value | (4,197) | (2,181)
Total derivatives not designated as hedging instruments, Fair Value | (4,166) | $ (783)
Derivatives designated as cash flow hedges, Derivatives assets, Fair Value | $ 59 |

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