PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Economic Assumptions and Impact of Change in Discount Rate on Benefit Obligation) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 27, 2021	Jun. 28, 2020	Dec. 27, 2020
Assumptions used to measure net pension and other postretirement cost
Increase in Discount Rate of 0.25% - Impact on defined benefit obligation for pension benefits	$ (10,162)
Decrease in Discount Rate of 0.25% - Impact on defined benefit obligation for pension benefits	$ 10,698
Pension Benefits
Assumptions used to measure benefit obligation at end of period
Discount rate	2.31%		1.83%
Assumptions used to measure net pension and other postretirement cost
Discount rate	1.86%	2.57%
Expected return on plan assets	3.53%	4.67%
Other Benefits
Assumptions used to measure benefit obligation at end of period
Discount rate	2.20%		1.80%
Assumptions used to measure net pension and other postretirement cost
Discount rate	1.80%	2.77%