Goodwill and Intangible Assets - Gross Amount and Accumulated Amortization of Acquired Finite-lived Intangibles (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2025	Sep. 29, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 248,531	$ 314,846
Accumulated Amortization	(127,371)	(154,261)
Net Amount	$ 121,160	160,585
Client relations
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in years)	7 years 3 months 18 days
Gross Amount	$ 169,807	198,726
Accumulated Amortization	(56,241)	(57,975)
Net Amount	$ 113,566	140,751
Backlog
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in years)	1 year
Gross Amount	$ 43,919	75,194
Accumulated Amortization	(40,397)	(71,101)
Net Amount	$ 3,522	4,093
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in years)	6 months
Gross Amount	$ 34,805	40,926
Accumulated Amortization	(30,733)	(25,185)
Net Amount	$ 4,072	$ 15,741