Derivative Financial Instruments and Fair Value Measurements - Derivatives Recorded at Fair Value in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 1,431	$ 2,416
Derivative Liabilities	1,844	12
Current | Derivatives not designated as Hedging Instruments | Commodities Contracts
Derivatives, Fair Value [Line Items]
Derivative Assets	1,431	2,416
Derivative Liabilities	1,829	12
Non-current | Derivatives not designated as Hedging Instruments | Commodities Contracts
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	$ 15	$ 0