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
Beginning balance ( in shares) at Dec. 31, 2017		11,534
Beginning 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)
Ending balance (in shares) at Mar. 31, 2018		11,543
Ending balance at Mar. 31, 2018	466,382	$ 1,158	104,588	(426)	387,985	(26,923)
Beginning balance ( in shares) at Dec. 31, 2017		11,534
Beginning 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
Ending balance (in shares) at Sep. 30, 2018		11,618
Ending balance at Sep. 30, 2018	496,892	$ 1,166	107,737	(426)	427,737	(39,322)
Beginning balance ( in shares) at Mar. 31, 2018		11,543
Beginning 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)
Ending balance (in shares) at Jun. 30, 2018		11,610
Ending balance at Jun. 30, 2018	474,447	$ 1,165	106,794	(426)	405,479	(38,565)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,543				23,543
Translation adjustment	(924)					(924)
Net actuarial gain arising during period, net of taxes	167					167
Stock-based compensation	622		622
Common stock repurchase	1		1
Exercise of stock options (in shares)		8
Exercise of stock options	321	$ 1	320
Dividends paid	(1,285)				(1,285)
Ending balance (in shares) at Sep. 30, 2018		11,618
Ending balance at Sep. 30, 2018	496,892	$ 1,166	107,737	(426)	427,737	(39,322)
Beginning balance ( in shares) at Dec. 31, 2018		11,620
Beginning 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)
Ending balance (in shares) at Mar. 31, 2019		11,616
Ending balance at Mar. 31, 2019	521,484	$ 1,167	109,285	(1,916)	456,889	(43,941)
Beginning balance ( in shares) at Dec. 31, 2018		11,620
Beginning 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	53,338				53,338
Ending balance (in shares) at Sep. 30, 2019		11,665
Ending balance at Sep. 30, 2019	551,052	$ 1,175	112,629	(4,566)	492,161	(50,347)
Beginning balance ( in shares) at Mar. 31, 2019		11,616
Beginning 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
Unrealized derivative gain (loss), net of taxes	(12)					(12)
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)
Ending balance (in shares) at Jun. 30, 2019		11,665
Ending balance at Jun. 30, 2019	542,832	$ 1,174	111,476	(3,381)	476,152	(42,589)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,418				17,418
Translation adjustment	(9,791)					(9,791)
Unrealized derivative gain (loss), net of taxes	1,864					1,864
Net actuarial gain arising during period, net of taxes	169					169
Stock-based compensation	766		766
Common stock repurchase (in shares)		(10)
Common stock repurchase	(1,185)			(1,185)
Exercise of stock options (in shares)		10
Exercise of stock options	388	$ 1	387
Dividends paid	(1,409)				(1,409)
Ending balance (in shares) at Sep. 30, 2019		11,665
Ending balance at Sep. 30, 2019	$ 551,052	$ 1,175	$ 112,629	$ (4,566)	$ 492,161	$ (50,347)