Forgivable Loans (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 26, 2020	Dec. 28, 2019
Forgivable Loans
Allowances for forgivable loans	$ 0	$ 0
Amount of forgivable loans written-off	0	0
Forgivable loan activity
Beginning balance	55,141,000	40,294,000
Advances	38,478,000	35,166,000
Repayments	0	(1,173,000)
Reclassification from accrued expenses / to other assets	(9,713,000)	(1,734,000)
Amortization	(19,517,000)	(17,700,000)
Effects of foreign currency translation	(214,000)	288,000
Ending balance	64,175,000	55,141,000
Current portion of forgivable loans	6,037,000	6,751,000
Non-current portion of forgivable loans	$ 58,138,000	$ 48,390,000