Information Related to Effect of Derivative Instruments on Our Consolidated Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	$ 259	$ (1,021)	$ 3,620	$ (354)
Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	132	(18)	209	34
Other comprehensive income | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	(1,234)	(868)	2,541	(624)
Other comprehensive income | Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	136	139	184	544
Product revenues | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	54		54
Cost of sales | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	1,424	(112)	1,303	23
Cost of sales | Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	(4)	(157)	25	(510)
Selling, general and administrative expense | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives			(216)	139
Foreign currency (loss) gain | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	$ 15	$ (41)	$ (62)	$ 108