Business Segments and Geographic Information - Revenues by Geography (Detail)	3 Months Ended		6 Months Ended
	Mar. 30, 2019	Mar. 31, 2018	Mar. 30, 2019	Mar. 31, 2018
Schedule Of Geographical Segments [Line Items]
Revenues	100.00%	100.00%	100.00%	100.00%
United States
Schedule Of Geographical Segments [Line Items]
Revenues	75.10%	74.50%	75.00%	75.00%
Europe
Schedule Of Geographical Segments [Line Items]
Revenues	12.50%	12.60%	12.30%	12.00%
Asia-Pacific
Schedule Of Geographical Segments [Line Items]
Revenues	7.90%	7.90%	8.10%	8.30%
Rest of World
Schedule Of Geographical Segments [Line Items]
Revenues	4.50%	5.00%	4.60%	4.70%