CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Total
Balance, beginning at Dec. 31, 2016	$ 31	$ 63,103	$ 402,714	$ (57,982)	$ (37,475)	$ 113,267
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		839
Share based compensation		703	536			391
Purchase of subsidiary shares from noncontrolling interest
Net income			37,194			12,287	49,481
Dividends			(15,899)			(5,947)
Foreign currency translation adjustment, net of tax				34,882		13,833	48,715
Transfer from other comprehensive income into earnings				17		5
Net derivative instrument gain (loss), net of tax				22		8
Balance, ending at Sep. 30, 2017	31	64,645	424,545	(23,061)	(37,475)	133,844	562,529
Balance, beginning at Dec. 31, 2017	31	66,004	422,570	(17,832)	(37,475)	137,339	570,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		2,384
Share based compensation		849	495			262
Purchase of subsidiary shares from noncontrolling interest		(572)				(236)	808
Net income			45,746			14,801	60,547
Dividends			(19,726)			(8,706)
Foreign currency translation adjustment, net of tax				(12,558)		(4,729)	(17,287)
Transfer from other comprehensive income into earnings				4
Net derivative instrument gain (loss), net of tax				(37)		(12)
Balance, ending at Sep. 30, 2018	$ 31	$ 68,665	$ 449,085	$ (30,423)	$ (37,475)	$ 138,719	$ 588,602