Derivative Financial Instruments and Fair Value Measurements - Derivatives Recorded at Fair Value in Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 2	$ 969
Derivative Liability, Fair Value, Gross Liability	4,392	318
Designated As Hedging Instrument | Commodities Contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	714
Derivative Liability, Fair Value, Gross Liability	0	204
Not Designated As Hedging Instruments | Commodities Contracts
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	2	255
Derivative Liability, Fair Value, Gross Liability	$ 4,392	$ 114