Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 0		$ (254)	$ 254
Balance, shares at Dec. 31, 2016		32,085				530
Balance, value at Dec. 31, 2016	460,880	$ 320	264,418	211,748	$ (7,721)	$ (7,885)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,384
Foreign currency translation adjustment	3,351				3,351
Adjustment to retirement benefit liability, net of taxes of ($5)	(8)				(8)
Adjustment to post employment health care benefit liability, net of taxes of $54	88				88
Stock compensation expense	5,069		5,069
Stock options exercised, shares		40
Stock options exercised	649	$ 0	649
Issuance of restricted stock, shares		2
Issuance of restricted stock	0	$ 0	0
Net settlement of restricted stock units, shares		148				58
Net settlement of restricted stock units	(1,982)	$ 2	(2)			$ (1,982)
Balance, shares at Sep. 30, 2017		32,275				588
Balance, value at Sep. 30, 2017	$ 505,431	$ 322	$ 269,880	$ 249,386	$ (4,290)	$ (9,867)