Stockholders' Equity and Stock-Based Compensation - Stock-Based Compensation Expense in Consolidated Statement of Operations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 29, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 50.0	$ 52.3	$ 40.6
Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7.3	7.0	5.7
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8.4	7.2	5.3
Selling and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	8.2	8.9	7.4
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	19.5	20.2	18.7
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6.6	$ 9.0	$ 3.5