Interim Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 6 months ended Jun. 30, 2018 - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Balance (shares) at Dec. 31, 2017		11,534
Balance at Dec. 31, 2017	$ 449,108	$ 1,158	$ 103,864	$ (426)	$ 374,678	$ (30,166)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,354				33,354
Translation adjustment	(8,733)					(8,733)
Net actuarial gain arising during period, net of taxes	334					334
Stock-based compensation	1,188		1,188
Exercise of stock options (shares)		76
Exercise of stock options	1,749	$ 7	1,742
Dividends paid ($0.22 per share)	(2,553)				(2,553)
Balance (shares) at Jun. 30, 2018		11,610
Balance at Jun. 30, 2018	$ 474,447	$ 1,165	$ 106,794	$ (426)	$ 405,479	$ (38,565)