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Information Related to Effect of Derivative Instrument's on Our Consolidated Statements of Income (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives $ 2,180 $ (1,762)
Commodity Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives 256 77
Other comprehensive (loss) income | Foreign Currency Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives 302 (1,395)
Other comprehensive (loss) income | Commodity Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives 54 743
Product Revenues | Foreign Currency Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives (3)  
Cost of sales | Foreign Currency Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives 2,209 (608)
Cost of sales | Commodity Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives 202 (666)
Selling, general and administrative expense | Foreign Currency Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives (216) 139
Foreign currency gain | Foreign Currency Derivatives    
Derivative Instruments Gain Loss [Line Items]    
Gain (loss) on derivatives $ (112) $ 102