Income Taxes - Components of Income Before Income Taxes and Reconciliation of Statutory Federal Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income before income taxes
United States	$ 281.4	$ 286.5	$ 242.7
Non-U.S.	10.9	(2.9)	(6.2)
Total income before income taxes	$ 292.3	$ 283.6	$ 236.5
U.S. statutory tax rate	21.00%	21.00%	21.00%
Income taxes computed at U.S. statutory tax rate	$ 61.4	$ 59.6	$ 49.7
(Decrease) increase in amount computed resulting from:
Unrecognized tax benefits	0.0	0.1	0.1
State taxes, net of federal benefit	15.0	9.2	11.2
International rate differential	0.7	(0.1)	0.1
Permanent items	1.3	1.7	0.1
Remeasurement of net deferred taxes	0.0	(0.1)	(1.1)
Return-to-provision adjustments	(0.1)	(0.7)	(0.9)
Change in valuation allowances	0.1	(1.7)	(27.7)
Tax Matters Agreement activity	(0.1)	0.0	5.4
Other	(0.8)	1.1	0.2
Income tax expense	$ 77.5	$ 69.1	$ 37.1
Effective tax rate	26.50%	24.40%	15.70%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231