Per Share Amounts and Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Equity [Abstract]
Net income	$ 24,627	$ 13,434	$ 54,585	$ 32,688
Weighted-average shares outstanding, basic	22,874,000	22,790,000	22,956,000	22,822,000
Weighted-average shares, partially-paid share subscriptions	0	3,000	0	8,000
Basic weighted average shares	22,874,000	22,793,000	22,956,000	22,830,000
Incremental shares from assumed exercise of stock subscription purchase rights	0	13,000	0	73,000
Incremental shares from assumed exercise of stock options and awards	980,000	1,196,000	1,046,000	1,024,000
Diluted weighted-average shares	23,854,000	24,002,000	24,002,000	23,927,000
Net income per share basic	$ 1.08	$ 0.59	$ 2.38	$ 1.43
Net income per share diluted	$ 1.03	$ 0.56	$ 2.27	$ 1.37
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2020			23,176,803
Shares purchased			(1,132,251)
Shares sold			658,715
Options and awards exercised			145,297
Shares outstanding at September 26, 2020	22,848,564		22,848,564
Employee options exercisable	1,028,683		1,028,683
Common shares, net of treasury shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2020			18,029,921
Shares purchased			(763,901)
Shares sold			263,212
Options and awards exercised			145,297
Shares outstanding at September 26, 2020	17,674,529		17,674,529
Redeemable shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2020			5,146,882
Shares purchased			(368,350)
Shares sold			395,503
Options and awards exercised			0
Shares outstanding at September 26, 2020	5,174,035		5,174,035