Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Balance, shares at Dec. 31, 2014		31,342,000				429,000
Balance at Dec. 31, 2014	$ 387,229	$ 313	$ 247,232	$ 154,625	$ (9,551)	$ (5,390)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,448			23,448
Foreign currency translation adjustment	(6,228)				(6,228)
Adjustment to retirement benefit liability, net of tax	49				49
Adjustment to post-retirement healthcare benefit liability, net of taxes	171				171
Unrealized loss on cash flow hedges, net of tax	(143)				(143)
Stock compensation expense	3,891		3,891
Cumulative effect of accounting change (see Note 1)	537		537
Net settlement of restricted stock units, shares		297,000				55,000
Net settlement of restricted stock units	$ (956)	$ 3	(3)			$ (956)
Issuance of restricted stock, shares		21,000
Stock options exercised, shares	119,096	119,000
Stock options exercised	$ 1,802	$ 1	1,801
Balance, shares at Dec. 31, 2015		31,779,000				484,000
Balance at Dec. 31, 2015	410,086	$ 317	253,458	178,073	(15,416)	$ (6,346)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	33,675			33,675
Foreign currency translation adjustment	6,945				6,945
Adjustment to retirement benefit liability, net of tax	55				55
Adjustment to post-retirement healthcare benefit liability, net of taxes	695				695
Unrealized loss on cash flow hedges, net of tax	0
Stock compensation expense	6,373		6,373
Cumulative effect of accounting change (see Note 1)	1,249		1,249
Net settlement of restricted stock units, shares		131,000				46,000
Net settlement of restricted stock units	$ (1,539)	$ 1	(1)			$ (1,539)
Stock options exercised, shares	175,125	175,000
Stock options exercised	$ 3,341	$ 2	3,339
Balance, shares at Dec. 31, 2016		32,085,000				530,000
Balance at Dec. 31, 2016	460,880	$ 320	264,418	211,748	(7,721)	$ (7,885)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	62,560			62,560
Foreign currency translation adjustment	3,150				3,150
Adjustment to retirement benefit liability, net of tax	(9)				(9)
Adjustment to post-retirement healthcare benefit liability, net of taxes	214				214
Unrealized loss on cash flow hedges, net of tax	0
Stock compensation expense	7,122		7,122
Cumulative effect of accounting change (see Note 1)	0		(254)	254
Net settlement of restricted stock units, shares		203,000				85,000
Net settlement of restricted stock units	$ (2,872)	$ 3	(3)			$ (2,872)
Issuance of restricted stock, shares		2,000
Stock options exercised, shares	42,058	42,000
Stock options exercised	$ 674		674
Balance, shares at Dec. 31, 2017		32,332,000				615,000
Balance at Dec. 31, 2017	$ 531,719	$ 323	$ 271,957	$ 274,562	$ (4,366)	$ (10,757)