Share-Based Payments - Share-based payments (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 27, 2020 USD ($) employee	Jun. 29, 2019 USD ($)	Jun. 27, 2020 USD ($) employee shares	Jun. 29, 2019 USD ($) shares	Dec. 28, 2019
Compensation expense
Total compensation expense for share-based payments	$ 3,821	$ 1,384	$ 4,244	$ 1,964
Number of employee | employee	2,922		2,922
Additional pre-tax share based compensation expense		700
LTIA 2019-2021 Plan [Member]
Compensation expense
Total compensation expense for share-based payments	$ 2,300
Board Members
Compensation expense
Vested Options With Extended Time Period | shares				48,727
Retired Executives [Member]
Compensation expense
Vested Options With Extended Time Period | shares				578,149
Unvested Options With Extended Time Period | shares				31,384
Performance shares
Compensation expense
Unrecognized compensation expense	7,200		$ 7,200
Period over which unrecognized compensation expense is expected to be recognized			2 years 1 month 6 days
Restricted Stock
Compensation expense
Total compensation expense for share-based payments			$ 1,500
Period over which unrecognized compensation expense is expected to be recognized			2 years 4 months 24 days
Stock Option
Compensation expense
Unrecognized compensation expense	300		$ 300
Period over which unrecognized compensation expense is expected to be recognized			8 months 12 days
Additional pre-tax share based compensation expense			$ 100
Stock Option | Retired Executives [Member]
Compensation expense
Vested options, extended post-retirement exercise period			3 years		180 days
Vested Options With Extended Time Period | shares			83,759
Cost of Goods Sold
Compensation expense
Total compensation expense for share-based payments	1,157	157	$ 1,174	$ 330
Selling, General and Administrative Expenses
Compensation expense
Total compensation expense for share-based payments	$ 2,664	$ 1,227	$ 3,070	$ 1,634