Interim Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 3 months ended Mar. 31, 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	14,583				14,583
Translation adjustment	3,117					3,117
Net actuarial gain arising during period, net of taxes	126					126
Stock-based compensation	458		458
Exercise of stock options (shares)		9
Exercise of stock options	266		266
Dividends paid ($0.11 per share)	(1,276)				(1,276)
Balance (shares) at Mar. 31, 2018		11,543
Balance at Mar. 31, 2018	$ 466,382	$ 1,158	$ 104,588	$ (426)	$ 387,985	$ (26,923)