Consolidated Statements of Changes in Shareholders' Equity - 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, 2015	$ 31	$ 62,030	$ 388,434	$ (48,091)	$ (36,817)	$ 110,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		2,160			142
Shares received as proceeds of option exercises					(800)
Stock-based compensation		839	222			147
Sale of subsidiary shares to noncontrolling interests		(173)				1,738
Purchase of subsidiary shares from noncontrolling interest		(1,753)				(1,188)
Net income			33,331			9,917	$ 43,248
Dividends			(19,273)			(4,863)
Foreign currency translation adjustment, net of tax				(9,874)		(3,279)	(13,153)
Transfer from other comprehensive income into earnings
Net derivative instrument gain, net of tax				(17)		(5)
Balance, ending at Dec. 31, 2016	31	63,103	402,714	(57,982)	(37,475)	113,267	483,658
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		1,963
Shares received as proceeds of option exercises
Stock-based compensation		938	722			531
Sale of subsidiary shares to noncontrolling interests
Purchase of subsidiary shares from noncontrolling interest
Net income			41,594			13,659	55,253
Dividends			(22,460)			(6,039)
Foreign currency translation adjustment, net of tax				40,096		15,899	55,995
Transfer from other comprehensive income into earnings				17		5
Net derivative instrument gain, net of tax				37		17
Balance, ending 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		3,406
Shares received as proceeds of option exercises
Stock-based compensation		1,132	724			419
Sale of subsidiary shares to noncontrolling interests
Purchase of subsidiary shares from noncontrolling interest		(572)				(236)
Net income			53,793			15,922	69,715
Dividends			(28,356)			(8,706)
Foreign currency translation adjustment, net of tax				(15,917)		(6,638)	(22,555)
Transfer from other comprehensive income into earnings				(37)
Net derivative instrument gain, net of tax				136		39
Balance, ending at Dec. 31, 2018	$ 31	$ 69,970	$ 448,731	$ (33,650)	$ (37,475)	$ 138,139	$ 585,746