Employee Future Benefits (Information about the Plans) (Details) - USD ($)	12 Months Ended
	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement loss	$ (5,651,000)	$ 0	$ 0
Defined contribution plan, contributions	12,400,000	11,800,000	7,800,000
UNITED KINGDOM | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	685,000	648,000	685,000
Expected return on assets	(948,000)	(990,000)	(429,000)
Amortization of actuarial net losses	246,000	142,000	0
Net pension expense	(17,000)	(200,000)	256,000
UNITED STATES
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Investment valued at NAV	8,000,000.0
Investment valued at NAV, redemptions requiring five-day notice	200,000
Unfunded commitments	0
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	548,000	670,000	811,000
Interest cost	3,423,000	3,322,000	3,421,000
Expected return on assets	(5,723,000)	(6,253,000)	(5,852,000)
Amortization of actuarial net losses	1,521,000	1,149,000	1,113,000
Settlement loss	5,651,000	0	0
Net pension expense	$ 5,420,000	$ (1,112,000)	$ (507,000)