Interim Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 9 months ended Sep. 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	56,897
Translation adjustment	(9,657)					(9,657)
Net actuarial gain arising during period, net of taxes	501					501
Stock-based compensation	1,810		1,810
Exercise of stock options (shares)		84
Exercise of stock options	2,071	$ 8	2,063
Dividends paid ($0.22 per share)	(3,838)				(3,838)
Balance (shares) at Sep. 30, 2018		11,618
Balance at Sep. 30, 2018	$ 496,892	$ 1,166	$ 107,737	$ (426)	$ 427,737	$ (39,322)