Consolidated Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 20,223	$ 27,665	$ 50,562	$ 66,979
Other comprehensive loss, gross of tax:
Foreign currency translation adjustments gain (loss)	2,230	(4,429)	2,866	(19,312)
Unrealized loss on foreign currency derivative securities	(868)	(460)	(624)	(1,237)
Unrealized gain (loss) on commodity derivative securities	139	(373)	544	(421)
Other comprehensive income (loss), gross of tax	1,501	(5,262)	2,786	(20,970)
Other comprehensive income (loss), related tax effect:
Foreign currency translation adjustments gain (loss)	(13)	51	1,087	764
Unrealized loss on foreign currency derivative securities	233	125	168	335
Unrealized gain (loss) on commodity derivative securities	(51)	155	(201)	155
Other comprehensive income (loss), related tax effect	169	331	1,054	1,254
Other comprehensive income (loss), net of tax	1,670	(4,931)	3,840	(19,716)
Comprehensive income	$ 21,893	$ 22,734	$ 54,402	$ 47,263