Per Share Amounts and Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Equity [Abstract]
Net loss	$ (493)	$ (6,627)
Weighted-average shares outstanding, basic	22,910,000	25,229,000
Weighted-average shares, partially-paid share subscriptions	162,000	189,000
Basic weighted average shares	23,072,000	25,418,000
Incremental shares from assumed exercise of stock subscription purchase rights	119,000	146,000
Incremental shares from assumed exercise of stock options and awards	827,000	912,000
Diluted weighted-average shares	24,018,000	26,476,000
Net loss per share--basic and diluted	$ (0.02)	$ (0.26)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2019	22,880,652
Shares purchased	(210,078)
Shares sold	209,416
Stock subscription offering -- cash purchases	39,636
Options and awards exercised	6,874
Shares outstanding at March 30, 2019	22,926,500
Common stock, shares subscribed but unissued	650,538
Purchase rights, outstanding	240,780
Common shares, net of treasury shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2019	17,238,497
Shares purchased	(195,048)
Shares sold	0
Stock subscription offering -- cash purchases	39,636
Options and awards exercised	6,874
Shares outstanding at March 30, 2019	17,089,959
Redeemable shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2019	5,642,155
Shares purchased	(15,030)
Shares sold	209,416
Stock subscription offering -- cash purchases	0
Options and awards exercised	0
Shares outstanding at March 30, 2019	5,836,541
Stock option plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee options exercisable	887,114