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Summary of Significant Accounting Policies - Accounts Receivable Reserve Activity (Detail) - USD ($)
$ in Millions
12 Months Ended
Sep. 26, 2015
Sep. 27, 2014
Sep. 28, 2013
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Balance at Beginning of Period $ 12.0 $ 8.8 $ 6.4
Charged to Costs and Expenses 1.6 4.4 4.3
Write- offs and Payments (2.5) (1.2) (1.9)
Balance at End of Period $ 11.1 $ 12.0 $ 8.8