DEFINED BENEFIT RETIREMENT PLAN (Details 2) £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 26, 2020 USD ($)	Dec. 26, 2020 GBP (£)	Dec. 28, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Limit on employer contributions per annum	$ 17,765	£ 13,100
Administrative costs of the Plan	1,763	£ 1,300
Plan assets	741,650		$ 604,396
Estimated Fair value
Defined Benefit Plan Disclosure [Line Items]
Plan assets	31,935		38,388
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	31,935		38,388
Fair Value Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 709,715		566,008
Mutual funds and diversified growth funds
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage	50.00%
Temporary cash investments | Estimated Fair value
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 31,935		38,388
Temporary cash investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	31,935		38,388
Corporate stock | Estimated Fair value
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Corporate stock | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Corporate stock | Fair Value Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets	309,987		234,612
Leveraged inflation-linked gilt funds | Fair Value Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets	171,013		123,637
Corporate bonds | Fair Value Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets	115,577		97,638
Secured income asset funds | Fair Value Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 113,138		$ 110,121