PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Net Defined Benefit Pension and Other Postretirement Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2021	Jun. 28, 2020	Jun. 27, 2021	Jun. 28, 2020
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Interest cost	$ 987	$ 2,011	$ 2,437	$ 4,050
Estimated return on plan assets	(1,815)	(3,215)	(4,456)	(6,498)
Settlement loss	837	0	837	0
Expenses paid from assets	91	93	169	537
Amortization of net loss	381	375	946	751
Amortization of past service cost	3	0	8	0
Net costs	484	(736)	(59)	(1,160)
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Interest cost	3	9	8	18
Estimated return on plan assets	0	0	0	0
Settlement loss	0	0	0	0
Expenses paid from assets	0	0	0	0
Amortization of net loss	0	0	1	0
Amortization of past service cost	0	0	0	0
Net costs	$ 3	$ 9	$ 9	$ 18