Interim Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Balance ( in 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 (in shares)		9
Exercise of stock options	266		266
Dividends paid	(1,276)				(1,276)
Balance (in shares) at Mar. 31, 2018		11,543
Balance at Mar. 31, 2018	466,382	$ 1,158	104,588	(426)	387,985	(26,923)
Balance ( in 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
Balance (in shares) at Jun. 30, 2018		11,610
Balance at Jun. 30, 2018	474,447	$ 1,165	106,794	(426)	405,479	(38,565)
Balance ( in shares) at Mar. 31, 2018		11,543
Balance at Mar. 31, 2018	466,382	$ 1,158	104,588	(426)	387,985	(26,923)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,771				18,771
Translation adjustment	(11,850)					(11,850)
Net actuarial gain arising during period, net of taxes	208					208
Stock-based compensation	730		730
Common stock repurchase	(437)		(437)
Exercise of stock options (in shares)		67
Exercise of stock options	1,920	$ 7	1,913
Dividends paid	(1,277)				(1,277)
Balance (in shares) at Jun. 30, 2018		11,610
Balance at Jun. 30, 2018	474,447	$ 1,165	106,794	(426)	405,479	(38,565)
Balance ( in shares) at Dec. 31, 2018		11,620
Balance at Dec. 31, 2018	507,371	$ 1,166	108,422	(426)	443,040	(44,831)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,253				15,253
Translation adjustment	720					720
Net actuarial gain arising during period, net of taxes	170					170
Stock-based compensation	627		627
Common stock repurchase (in shares)		(15)
Common stock repurchase	(1,490)			(1,490)
Exercise of stock options (in shares)		11
Exercise of stock options	237	$ 1	236
Dividends paid	(1,404)				(1,404)
Balance (in shares) at Mar. 31, 2019		11,616
Balance at Mar. 31, 2019	521,484	$ 1,167	109,285	(1,916)	456,889	(43,941)
Balance ( in shares) at Dec. 31, 2018		11,620
Balance at Dec. 31, 2018	507,371	$ 1,166	108,422	(426)	443,040	(44,831)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,920				35,920
Balance (in shares) at Jun. 30, 2019		11,665
Balance at Jun. 30, 2019	542,832	$ 1,174	111,476	(3,381)	476,152	(42,589)
Balance ( in shares) at Mar. 31, 2019		11,616
Balance at Mar. 31, 2019	521,484	$ 1,167	109,285	(1,916)	456,889	(43,941)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,667				20,667
Translation adjustment	1,194					1,194
Net actuarial gain arising during period, net of taxes	170					170
Stock-based compensation	948		948
Common stock repurchase (in shares)		(15)
Common stock repurchase	(2,055)		(590)	(1,465)
Exercise of stock options (in shares)		64
Exercise of stock options	1,840	$ 7	1,833
Dividends paid	(1,404)				(1,404)
Balance (in shares) at Jun. 30, 2019		11,665
Balance at Jun. 30, 2019	542,832	$ 1,174	$ 111,476	$ (3,381)	$ 476,152	(42,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized loss during the period related to derivatives	$ (12)					$ (12)