Consolidated Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 12,966	$ 25,402
Other comprehensive income (loss), gross of tax:
Foreign currency translation adjustments gain	11,741	5,515
Unrealized gain on foreign currency derivative securities	2,112	2,960
Unrealized (loss) gain on commodity derivative securities	(218)	32
Other comprehensive income, gross of tax	13,635	8,507
Other comprehensive income (loss), related tax effect:
Cumulative effect of accounting change due to ASU 2018-02	(40)
Foreign currency translation adjustments gain	(76)	(3)
Unrealized gain on foreign currency derivative securities	(567)	(795)
Unrealized (loss) gain on commodity derivative securities	(59)	(11)
Other comprehensive income (loss), related tax effect	(742)	(809)
Other comprehensive income, net of tax	12,893	7,698
Comprehensive income	$ 25,859	$ 33,100