Statements of Consolidated Shareholders' Equity - USD ($) $ in Thousands	Total	Common shares	Additional paid-in capital	Common shares subscribed, unissued	Retained earnings	Accumulated other comprehensive income (loss), net of tax	Common shares held in treasury	Common shares subscription receivable
Balance at beginning of year, value at Dec. 31, 2013		$ 21,457	$ 5,008	$ 10,467	$ 230,975		$ (125,034)	$ 7,342
Common shares, at beginning of year at Dec. 31, 2013		21,457,000
Share subscriptions, beginning balance, shares at Dec. 31, 2013				(531,000)				(531,000)
Balance at beginning of year, shares at Dec. 31, 2013							8,018,000
Balance at the beginning of the year at Dec. 31, 2013	$ (4,393)					$ (4,393)
Increase (decrease) in stockholders' equity [Roll Forward]
Shares purchased, value							$ (19,598)
Shares sold to employees, value			3,417				3,822
Options exercised, value			(273)				(1,861)
Subscription shares, issued, value			184				$ 794
Stock-based compensation			1,125
Common shares, subscribed, value				$ 0				$ 0
Common shares, subscribed, shares				0				0
Common shares, issued, value				$ (758)				$ (1,543)
Common shares, issued, shares				(39,000)				(39,000)
Cancellations, value				$ (328)				$ (199)
Cancellations, shares				(16,000)				(16,000)
Net income	23,169				23,169
Dividends					(2,674)
Currency translation adjustments						(2,798)
Defined benefit pension plans	4,332					(4,332)
Shares purchased, shares							727,000
Shares sold to employees, shares							(287,000)
Options exercised, shares							(116,000)
Subscription shares, issued, shares							(50,000)
Balance at ending of year, value at Dec. 31, 2014	$ 136,491	$ 21,457	9,461	$ 9,381	251,470		$ (138,155)	$ 5,600
Share subscriptions, ending balance, shares at Dec. 31, 2014				(476,000)				(476,000)
Balance at ending of year, shares at Dec. 31, 2014	13,165,000						8,292,000
Balance at the end of the year at Dec. 31, 2014	$ (11,523)					(11,523)
Common shares, at end of year at Dec. 31, 2014	21,456,880	21,457,000
Increase (decrease) in stockholders' equity [Roll Forward]
Shares purchased, value							$ (25,395)
Shares sold to employees, value			6,066				2,198
Options exercised, value			(152)				(1,225)
Subscription shares, issued, value			83				$ 698
Stock-based compensation			2,357
Common shares, subscribed, value				$ 0				$ 0
Common shares, subscribed, shares				0				0
Common shares, issued, value				$ (676)				$ (1,434)
Common shares, issued, shares				(34,000)				(34,000)
Cancellations, value				$ (114)				$ (60)
Cancellations, shares				(6,000)				(6,000)
Net income	$ 21,798				21,798
Dividends					(2,663)
Currency translation adjustments						(5,093)
Defined benefit pension plans	$ (3,222)					3,222
Shares purchased, shares	823,827						824,000
Shares sold to employees, shares	(287,875)						(288,000)
Options exercised, shares							(71,000)
Subscription shares, issued, shares							(43,000)
Balance at ending of year, value at Dec. 31, 2015	$ 141,539	$ 21,457	17,815	$ 8,591	270,605		$ (159,429)	$ 4,106
Share subscriptions, ending balance, shares at Dec. 31, 2015				(436,000)				(436,000)
Balance at ending of year, shares at Dec. 31, 2015	12,743,000						8,714,000
Balance at the end of the year at Dec. 31, 2015	$ (13,394)					(13,394)
Common shares, at end of year at Dec. 31, 2015	21,456,880	21,457,000
Increase (decrease) in stockholders' equity [Roll Forward]
Shares purchased, value							$ (25,290)
Shares sold to employees, value			4,182				5,298
Options exercised, value			(992)				(2,442)
Subscription shares, issued, value			21				$ 449
Stock-based compensation			2,860
Common shares, subscribed, value	$ (12,563)			$ 0				$ 0
Common shares, subscribed, shares	(637,714)			0				0
Common shares, issued, value				$ (325)				$ (1,104)
Common shares, issued, shares				(16,000)				(16,000)
Cancellations, value				$ (57)				$ (29)
Cancellations, shares				(3,000)				(3,000)
Net income	$ 22,284				22,284
Dividends					(2,597)
Currency translation adjustments						744
Defined benefit pension plans	$ (488)					488
Shares purchased, shares	746,041						746,000
Shares sold to employees, shares	(308,892)						(309,000)
Options exercised, shares	(137,696)						(131,000)
Subscription shares, issued, shares							(25,000)
Balance at ending of year, value at Dec. 31, 2016	$ 152,179	$ 21,457	$ 23,886	$ 8,209	$ 290,292		$ (176,530)	$ 2,973
Share subscriptions, ending balance, shares at Dec. 31, 2016				(417,000)				(417,000)
Balance at ending of year, shares at Dec. 31, 2016	12,462,000						8,995,000
Balance at the end of the year at Dec. 31, 2016	$ (12,162)					$ (12,162)
Common shares, at end of year at Dec. 31, 2016	21,456,880	21,457,000