Profit Sharing 401(k) Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Contributions made by company	$ 20.2	$ 16.2	$ 14.4

Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration