Benefit Plans - Benefit Plan Related Information (Details) $ in Thousands, £ in Millions		3 Months Ended		12 Months Ended
	Apr. 06, 2020 USD ($)	Jun. 27, 2020 USD ($)	Jun. 27, 2020 GBP (£)	Dec. 26, 2020 USD ($)	Dec. 28, 2019 USD ($)	Dec. 29, 2018 USD ($)
Change in benefit obligation:
Benefit obligation at beginning of year				$ 2,800
Service cost				2,462	$ 2,040	$ 2,266
Interest cost				2,173	3,169	3,104
Net actuarial loss	$ (13,400)
Benefits paid from the plan assets		$ (10,400)	£ (8.4)
Benefit obligation at end of year				3,500	2,800
Change in plan assets at fair value:
Fair value of plan assets at beginning of year				78,502
Fair value of plan assets at end of year				100,478	78,502
Amounts recognized in the Consolidated Balance Sheets consist of:
Noncurrent assets				39	885
Current benefit liability				(2,751)	(1,106)
Noncurrent benefit liability				(45,802)	(38,198)
Net liability recognized				(48,514)	(38,419)
Pension Plan
Change in benefit obligation:
Benefit obligation at beginning of year				116,921	102,833
Service cost				2,462	2,040
Interest cost				2,173	3,169
Net actuarial loss				25,306	11,286
Benefits paid from the plan assets				(2,808)	(3,323)
Benefits paid directly by the Company				(2,302)	(1,540)
Curtailments and Settlements				102	(1,924)
Effect of exchange rate movements				7,462	1,735
Plan amendment and other				(324)	2,645
Benefit obligation at end of year				148,992	116,921	102,833
Change in plan assets at fair value:
Fair value of plan assets at beginning of year				78,502	70,676
Actual return on plan assets				7,053	8,222
Employer contributions				12,918	2,233
Benefits paid from the plan assets				(2,808)	(3,323)
Settlements				0	(1,072)
Effect of exchange rate movements				4,813	1,766
Fair value of plan assets at end of year				100,478	78,502	$ 70,676
Net amount unfunded status				$ (48,514)	$ (38,419)