PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2021	Mar. 29, 2020	Dec. 27, 2020	Dec. 29, 2019
Change in plan assets
Fair value of plan assets, beginning of period	$ 305,983
Fair value of plan assets, end of period	312,429
Pension Benefits
Change in projected benefit obligation
Projected benefit obligation, beginning of period	404,194	$ 369,066
Interest cost	1,450	2,039
Actuarial gain	(27,980)	(29,447)
Benefits paid	(4,583)	(4,746)
Prior service cost	0	6
Currency translation loss (gain)	3,674	(9,019)
Projected benefit obligation, end of period	376,755	327,899
Change in plan assets
Fair value of plan assets, beginning of period	305,983	294,589
Actual return on plan assets	4,291	(37,302)
Contributions by employer	3,916	2,172
Benefits paid	(4,828)	(4,746)
Expenses paid from assets	(78)	(438)
Currency translation gain (loss)	3,145	(8,226)
Fair value of plan assets, end of period	312,429	246,049
Funded status
Unfunded benefit obligation, end of period	(64,326)		$ (98,211)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period
Current liability	(2,962)		(7,510)
Long-term liability	(61,364)		(90,701)
Recognized liability	(64,326)		(98,211)
Amounts recognized in accumulated other comprehensive loss at end of period
Net actuarial loss	65,831	68,691	95,522	$ 58,239
Other Benefits
Change in projected benefit obligation
Projected benefit obligation, beginning of period	1,593	1,527
Interest cost	5	9
Actuarial gain	(53)	(17)
Benefits paid	(42)	(40)
Prior service cost	0	0
Currency translation loss (gain)	0	0
Projected benefit obligation, end of period	1,503	1,479
Change in plan assets
Fair value of plan assets, beginning of period	0	0
Actual return on plan assets	0	0
Contributions by employer	42	40
Benefits paid	(42)	(40)
Expenses paid from assets	0	0
Currency translation gain (loss)	0	0
Fair value of plan assets, end of period	0	0
Funded status
Unfunded benefit obligation, end of period	(1,503)		(1,593)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period
Current liability	(168)		(169)
Long-term liability	(1,335)		(1,424)
Recognized liability	(1,503)		(1,593)
Amounts recognized in accumulated other comprehensive loss at end of period
Net actuarial loss	$ 120	$ 74	$ 174	$ 91