Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Items [Member]	Noncontrolling Interest [Member]
Beginning balance (in shares) at Dec. 31, 2016		14,624,159			3,686,532
Beginning balance at Dec. 31, 2016	$ 284,279	$ 146	$ 101,405	$ 321,050	$ (90,335)	$ (49,637)	$ 1,650
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	17,265			17,047			218
Dividends declared	(4,621)			(4,621)
Activity under stock plans (in shares)					(66,694)
Activity under stock plans	530		(1,104)		$ 1,634
Other comprehensive items	13,884					13,721	163
Ending balance (in shares) at Jul. 01, 2017		14,624,159			3,619,838
Ending balance at Jul. 01, 2017	311,337	$ 146	100,301	333,476	$ (88,701)	(35,916)	2,031
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments for the adoption of ASC 2014-09 and ASU No. 2016-16 | ASU No. 2014-09 [Member]	119			119
Adjustments for the adoption of ASC 2014-09 and ASU No. 2016-16 | ASU No. 2016-16 [Member]	(75)			(75)
Beginning balance (in shares) at Dec. 30, 2017		14,624,159			3,613,838
Beginning balance at Dec. 30, 2017	332,504	$ 146	103,221	342,893	$ (88,554)	(26,715)	1,513
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	23,499			23,207			292
Dividends declared	(4,882)			(4,882)
Activity under stock plans (in shares)					(85,288)
Activity under stock plans	711		(1,379)		$ 2,090
Other comprehensive items	(10,191)					(10,138)	(53)
Ending balance (in shares) at Jun. 30, 2018		14,624,159			3,528,550
Ending balance at Jun. 30, 2018	$ 341,685	$ 146	$ 101,842	$ 361,262	$ (86,464)	$ (36,853)	$ 1,752