Business Segments and Geographic Information - Revenues by Geography (Detail)	12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 29, 2018
Schedule Of Geographical Segments [Line Items]
Revenues	100.00%	100.00%	100.00%
United States
Schedule Of Geographical Segments [Line Items]
Revenues	75.80%	75.30%	75.10%
Europe
Schedule Of Geographical Segments [Line Items]
Revenues	15.10%	11.80%	11.70%
Asia-Pacific
Schedule Of Geographical Segments [Line Items]
Revenues	6.00%	8.50%	8.60%
Rest of world
Schedule Of Geographical Segments [Line Items]
Revenues	3.10%	4.40%	4.60%