CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]	Noncontrolling interest [Member]
Balance at Dec. 31, 2014			$ 60,200	$ 374,121	$ (15,823)		$ 116,659
Net income	$ 37,459			28,578			8,881
Foreign currency translation adjustment	(33,031)				(24,092)		(8,939)
Shares issued upon exercise of stock options			451
Purchase of subsidiary shares from noncontrolling interests			0				0
Sale of subsidiary shares to noncontrolling interest			(6)				696
Stock-based compensation			590
Dividends				(12,089)			(3,836)
Balance at Sep. 30, 2015	488,958	$ 31	61,235	390,610	(39,915)	$ (36,464)	113,461
Balance at Dec. 31, 2015	476,387		62,030	388,434	(48,091)		110,800
Net income	38,656			29,404			9,252
Foreign currency translation adjustment	10,504				7,363		3,141
Shares issued upon exercise of stock options			1,235
Purchase of subsidiary shares from noncontrolling interests			(1,670)				(800)
Sale of subsidiary shares to noncontrolling interest			(154)				1,603
Stock-based compensation			630
Dividends				(13,980)			(4,863)
Balance at Sep. 30, 2016	$ 507,548	$ 31	$ 62,071	$ 403,858	$ (40,728)	$ (36,817)	$ 119,133