Income Taxes - Schedule of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of period	$ 8.2	$ 8.7	$ 13.4
Increases related to tax positions from prior years	0.6	0.1	1.5
Decreases related to tax positions from prior years	(0.6)	(0.6)	(1.3)
Increases related to tax positions taken during the current year	27.7	0.8	0.7
Settlements with tax authorities	0.0	0.0	(4.2)
Lapses of statutes of limitation	(0.2)	(0.8)	(1.4)
Unrecognized tax benefits, end of period	35.7	8.2	$ 8.7
Accrual for tax interest and penalties	$ 1.8	$ 1.2