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, 2017	$ 31	$ 66,004	$ 422,570	$ (17,832)	$ (37,475)	$ 137,339
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		1,003
Share-based compensation		281	155			127
Purchase of subsidiary shares from noncontrolling interest
Net income			15,909			5,953	$ 21,862
Dividends			(6,569)			(362)
Foreign currency translation adjustment, net of tax				9,473		3,770	13,243
Transfer from other comprehensive income into earnings				(30)		(8)
Net derivative instrument loss, net of tax				(37)		(26)
Balance, ending at Mar. 31, 2018	31	67,288	432,065	(8,426)	(37,475)	146,793	600,276
Balance, beginning at Dec. 31, 2018	31	69,970	448,731	(33,650)	(37,475)	138,139	585,746
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued upon exercise of stock options		2,251
Share-based compensation		350	353			321
Purchase of subsidiary shares from noncontrolling interest		(468)				(376)
Net income			18,894			6,084	24,978
Dividends			(8,649)
Foreign currency translation adjustment, net of tax				(6,304)		(2,241)	(8,545)
Transfer from other comprehensive income into earnings				(136)
Net derivative instrument loss, net of tax				(7)		(52)
Balance, ending at Mar. 31, 2019	$ 31	$ 72,103	$ 459,329	$ (40,097)	$ (37,475)	$ 141,875	$ 595,766