Business Segments and Geographic Information - Revenues by Geography (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Schedule Of Geographical Segments [Line Items]
Revenues	100.00%	100.00%	100.00%
United States
Schedule Of Geographical Segments [Line Items]
Revenues	77.60%	78.90%	76.00%
Europe
Schedule Of Geographical Segments [Line Items]
Revenues	10.00%	10.20%	11.80%
Asia-Pacific
Schedule Of Geographical Segments [Line Items]
Revenues	8.10%	7.60%	8.50%
Rest of world
Schedule Of Geographical Segments [Line Items]
Revenues	4.30%	3.30%	3.70%