Employee Future Benefits (Plan Activity) (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
UNITED KINGDOM
Pension assets:
Fair value of plan assets, beginning of year	$ 22,307	$ 25,141
Company contributions	1,265	661
Actual return on plan assets	3,201	(1,106)
Benefits paid	(863)	(886)
Translation adjustment	838	(1,503)
Fair value of plan assets, end of year	26,748	22,307	$ 25,141
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accrued benefit obligation, beginning of year	28,303	30,812
Interest cost	685	648	685
Actuarial loss (gain)	3,446	(962)
Benefits paid	(863)	(886)
Plan amendment	0	585
Translation adjustment	1,030	(1,894)
Accrued benefit obligation, end of year	32,601	28,303	30,812
Net accrued benefit obligation, end of year	5,853	5,996
UNITED STATES
Pension assets:
Fair value of plan assets, beginning of year	86,992	92,716
Company contributions	5,000	5,000
Actual return on plan assets	17,030	(4,453)
Benefits paid	(5,560)	(5,730)
Administration expenses paid	(484)	(541)
Fair value of plan assets, end of year	79,422	86,992	92,716
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accrued benefit obligation, beginning of year	95,171	104,909
Current service cost	548	670	811
Interest cost	3,423	3,322	3,421
Plan settlements	23,556	0
Actuarial loss (gain)	9,015	(7,459)
Benefits paid	(5,560)	(5,730)
Administration expenses paid	(484)	(541)
Accrued benefit obligation, end of year	78,557	95,171	$ 104,909
Net accrued benefit obligation, end of year	$ 865	$ (8,179)