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	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Asset, Fair Value	$ 455	$ 2
Liability, Fair Value	5,272	4,392
Level 1
Derivatives, Fair Value [Line Items]
Asset, Fair Value	0	0
Liability, Fair Value	0	0
Level 2
Derivatives, Fair Value [Line Items]
Asset, Fair Value	455	2
Liability, Fair Value	5,272	4,392
Level 3
Derivatives, Fair Value [Line Items]
Asset, Fair Value	0	0
Liability, Fair Value	$ 0	$ 0