Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2017 USD ($) Lease term	Sep. 24, 2016 USD ($)	Sep. 26, 2015 USD ($)
Contingent Consideration Earn-Out Payments [Line Items]
Accrued expenses	$ 375.3	$ 287.6
Operating lease expiration year	2035
Rent expense net of sublease income	$ 19.3	17.9	$ 19.2
Rent expense on sublease rentals	$ 2.3	$ 2.4	$ 2.0
Finance Leases [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Number of finance leases | Lease	2
Fair value	$ 28.3
Finance lease extension executed	1
Finance lease expiration year	2024
Accrued expenses	$ 3.2
Accrued lease obligation-long-term	$ 34.1
Optional lease extension period	10 years
Number of optional lease extensions | term	2
Lease extension period	5 years
Finance Lease 2 [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Optional lease extension period	8 years
Number of optional lease extensions | term	1
Lease extension period	5 years
Finance Leases [Member] | Leasehold Improvements [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Property, plant and equipment, estimated useful life	35 years