Intangible Assets, Goodwill, Acquisitions and Divestitures - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 6.2	$ 8.1
Intangible assets acquired	0.0	0.0
Goodwill	2,015.7		$ 2,015.7	$ 2,015.7
Net service revenues	614.7	$ 599.2
Maintenance Services segment
Finite Lived Intangible Assets [Line Items]
Goodwill	1,797.7		1,797.7	1,797.7
Development Services segment.
Finite Lived Intangible Assets [Line Items]
Goodwill	$ 218.0		$ 218.0	$ 218.0