Derivative Financial Instruments and Fair Value Measurements - Summary of Derivative Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Commodities Contracts - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Assets - Fair Value	$ 1,431	$ 2,416
Liabilities - Fair Value	1,844	12
Level 2
Derivatives, Fair Value [Line Items]
Assets - Fair Value	1,431	2,416
Liabilities - Fair Value	$ 1,844	$ 12