Employee Stock Plans - Net Share-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Oct. 02, 2015	Sep. 26, 2014	Sep. 27, 2013
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 46,303	$ 39,636	$ 42,637
Income tax benefit for share-based compensation	(14,198)	(12,062)	(12,989)
Cost of revenues - Product
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	4,753	3,323	4,088
Cost of revenues - Service
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	4,068	4,658	3,460
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	6,805	6,194	5,993
Selling, general and administrative expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 30,677	$ 25,461	$ 29,096