Goodwill and Intangible Assets - Gross Amount and Accumulated Amortization of Acquired Finite-lived Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 29, 2024	Sep. 29, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 299,023	$ 314,846
Accumulated Amortization	(156,926)	(154,261)
Net Amount	$ 142,097	160,585
Client relations
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	8 years
Gross Amount	$ 189,027	198,726
Accumulated Amortization	(60,294)	(57,975)
Net Amount	$ 128,733	140,751
Backlog
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	2 months 12 days
Gross Amount	$ 71,647	75,194
Accumulated Amortization	(70,405)	(71,101)
Net Amount	$ 1,242	4,093
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	1 year 2 months 12 days
Gross Amount	$ 38,349	40,926
Accumulated Amortization	(26,227)	(25,185)
Net Amount	$ 12,122	$ 15,741