Goodwill and Intangible Assets - Gross Amount and Accumulated Amortization of Acquired Finite-lived Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Oct. 01, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 280,622	$ 270,453
Accumulated Amortization	(112,488)	(96,517)
Net Amount	$ 168,134	173,936
Client relations
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	9 years 2 months 12 days
Gross Amount	$ 175,486	169,217
Accumulated Amortization	(41,572)	(36,072)
Net Amount	$ 133,914	133,145
Backlog
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	9 months 18 days
Gross Amount	$ 66,052	63,825
Accumulated Amortization	(54,960)	(47,802)
Net Amount	$ 11,092	16,023
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	2 years 1 month 6 days
Gross Amount	$ 39,084	37,411
Accumulated Amortization	(15,956)	(12,643)
Net Amount	$ 23,128	$ 24,768