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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	$ 2,155	$ 259	$ 2,223	$ 3,620
Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives		132	(73)	209
Other comprehensive income | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	1,753	(1,234)	2,304	2,541
Other comprehensive income | Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives		136	(218)	184
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	391	1,424	(214)	1,303
Cost of sales | Commodity Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives		(4)	145	25
Selling, general and administrative expense | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives			75	(216)
Foreign currency (loss) gain | Foreign Currency Derivatives
Derivative Instruments Gain Loss [Line Items]
Gain (loss) on derivatives	$ 11	$ 15	$ 58	$ (62)