Balance Sheet Components - Additional Information (Detail) - USD ($)	9 Months Ended
	Jul. 03, 2015	Sep. 26, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 90,900,000	$ 75,600,000
Available-for-sale securities, maturity term, greater than	1 year
Other-than-temporary impairment losses, investments, available-for-sale securities	$ 0
Corporate debt securities: CPTC loans
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	81,900,000	75,600,000
Tranche A loan | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	71,700,000	66,200,000
Tranche B loan | Other Assets
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 10,200,000	$ 9,400,000