Per Share Amounts and Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Equity [Abstract]
Net income	$ 29,785	$ 19,747	$ 29,958	$ 19,254
Weighted-average shares outstanding, basic	22,807,000	22,764,000	22,997,000	22,837,000
Weighted-average shares, partially-paid share subscriptions	0	151,000	0	302,000
Basic weighted average shares	22,807,000	22,915,000	22,997,000	23,139,000
Incremental shares from assumed exercise of stock subscription purchase rights	0	88,000	0	104,000
Incremental shares from assumed exercise of stock options and awards	1,176,000	1,048,000	1,080,000	937,000
Diluted weighted-average shares	23,983,000	24,051,000	24,077,000	24,180,000
Net income per share basic	$ 1.31	$ 0.86	$ 1.30	$ 0.83
Net income per share diluted	$ 1.24	$ 0.82	$ 1.24	$ 0.80
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2020			23,176,803
Shares purchased			(992,850)
Shares sold			571,099
Options and awards exercised			116,980
Shares outstanding at June 27, 2020	22,872,032		22,872,032
Employee options exercisable	1,060,493		1,060,493
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			(667,353)
Shares sold			263,096
Options and awards exercised			116,980
Shares outstanding at June 27, 2020	17,742,644		17,742,644
Redeemable shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding at January 1, 2020			5,146,882
Shares purchased			(325,497)
Shares sold			308,003
Options and awards exercised			0
Shares outstanding at June 27, 2020	5,129,388		5,129,388