Deferred Compensation Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 29, 2018
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	$ 57,700,000	$ 51,900,000
Nonqualified Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Maximum employee contributions from base salary, percentage	75.00%
Maximum employee contributions from annual bonus, percentage	100.00%
Employee contributions vested, percentage	100.00%
Percent vested annually	33.33%
Compensation expense for the DCP discretionary contributions	$ 3,100,000	2,700,000	$ 2,900,000
Investment in group life insurance contracts	$ 49,300,000	$ 44,600,000
Nonqualified Deferred Compensation Plan [Member] | One Third Annually [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions, vesting period, years	3 years