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	16,765
Foreign currency translation adjustment	1,770				1,770
Adjustment to retirement benefit liability, net of taxes of ($3)	(6)				(6)
Adjustment to post employment health care benefit liability, net of taxes of $36	59				59
Stock compensation expense	3,191		3,191
Stock options exercised, shares		16
Stock options exercised	247	$ 0	247
Issuance of restricted stock, shares		2
Issuance of restricted stock	0	$ 0	0
Net settlement of restricted stock units, shares		52				24
Net settlement of restricted stock units	(1,003)	$ 1	(1)			$ (1,003)
Balance, shares at Jun. 30, 2017		32,155				554
Balance, value at Jun. 30, 2017	$ 481,903	$ 321	$ 267,601	$ 228,767	$ (5,898)	$ (8,888)