PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Economic Assumptions, and Impact of Change in Discount Rate on Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 27, 2020	Dec. 29, 2019	Dec. 30, 2018
Net pension and other postretirement cost:
Increase in Discount Rate of 0.25% - impact on defined benefit obligation for pension benefits	$ (10,820)
Decrease in Discount Rate of 0.25% - impact on defined benefit obligation for pension benefits	$ 11,391
Pension Benefits
Benefit obligation:
Discount rate	1.83%	2.56%	4.40%
Net pension and other postretirement cost:
Discount rate	2.16%	3.10%	3.69%
Expected return on plan assets	4.34%	4.62%	5.50%
Other Benefits
Benefit obligation:
Discount rate	1.80%	2.77%	4.07%
Net pension and other postretirement cost:
Discount rate	2.77%	4.07%	3.39%