Recently Adopted Accounting Standards - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 26, 2020	Dec. 28, 2019	Dec. 29, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 508,518	$ 529,723
Allowance for doubtful accounts	$ 5,991	$ 3,559
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Fair value, measurements, recurring
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale debt securities	$ 13,200	$ 12,500
Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			$ (100)