Intangible Assets, Goodwill, Acquisitions and Divestitures - Additional Information (Details) $ in Millions			12 Months Ended
		Jan. 12, 2024 USD ($) Subsidiary	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets			$ 29.3	$ 35.8	$ 44.5
Intangible assets acquired			0.0	0.0
Consideration paid, net of cash acquired			0.0	0.0	13.8
Net service revenues			2,672.8	2,767.1	2,816.0
Number of sale of fully owned subsidiaries | Subsidiary		1
Cash consideration		$ 51.0	$ 0.0	$ 51.0	$ 0.0
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Statement of Income or Comprehensive Income [Extensible Enumeration]				Gain (Loss) on Disposition of Business
Pre-tax gain (loss) on sale of business	[1]			$ 43.6
Selling, General and Administrative Expense
Finite Lived Intangible Assets [Line Items]
Gain on Sale of Fully Owned Subsidiaries				$ 43.6

[1] Represents the realized gain on sale and transaction related expenses from the divestiture of U.S. Lawns on January 12, 2024.