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Leases and Rental Expense (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2017
Sep. 24, 2016
Sep. 26, 2015
Leases And Rental Expense [Abstract]      
Lease term 20 years    
Rent expense for all operating leases $ 13.6 $ 13.8 $ 13.6
Sub-lease rental income $ 0.2 $ 0.2 $ 0.2