PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Fair Value Assumptions of Plan Assets) (Details) - USD ($) $ in Thousands	Sep. 27, 2020	Dec. 29, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	$ 279,261	$ 294,589
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	6,819	11,582
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	272,442	283,007
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	6,819	11,582
Cash and cash equivalents | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	6,819	11,582
Cash and cash equivalents | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents | Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	2,962	3,071
Large U.S. equity funds | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	26,324	20,378
Large U.S. equity funds | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	35,091	17,756
Large U.S. equity funds | Level 1 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Level 1 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Level 1 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Level 2 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	2,962	3,071
Large U.S. equity funds | Level 2 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	26,324	20,378
Large U.S. equity funds | Level 2 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	35,091	17,756
Large U.S. equity funds | Level 3 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Level 3 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Large U.S. equity funds | Level 3 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Small/Mid U.S. equity funds | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	368	372
Small/Mid U.S. equity funds | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	13,763	12,495
Small/Mid U.S. equity funds | Level 1 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Small/Mid U.S. equity funds | Level 1 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Small/Mid U.S. equity funds | Level 2 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	368	372
Small/Mid U.S. equity funds | Level 2 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	13,763	12,495
Small/Mid U.S. equity funds | Level 3 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Small/Mid U.S. equity funds | Level 3 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	1,772	1,878
International equity funds | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	14,105	25,149
International equity funds | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	56,792	102,494
International equity funds | Level 1 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 1 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 1 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 2 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	1,772	1,878
International equity funds | Level 2 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	14,105	25,149
International equity funds | Level 2 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	56,792	102,494
International equity funds | Level 3 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 3 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
International equity funds | Level 3 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	5,037	4,452
Fixed income securities | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	37,365	35,627
Fixed income securities | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	57,223	53,722
Fixed income securities | Level 1 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Level 1 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Level 1 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Level 2 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	5,037	4,452
Fixed income securities | Level 2 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	37,365	35,627
Fixed income securities | Level 2 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	57,223	53,722
Fixed income securities | Level 3 | Union Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Level 3 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Fixed income securities | Level 3 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Real estate | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	5,664	5,613
Real estate | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	15,976	0
Real estate | Level 1 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Real estate | Level 1 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Real estate | Level 2 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	5,664	5,613
Real estate | Level 2 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	15,976	0
Real estate | Level 3 | GK Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	0	0
Real estate | Level 3 | U.K. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	$ 0	$ 0