Leases - Operating Lease Costs and Other Related Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease costs	$ 25.5	$ 17.2
Cash paid for amounts included in the measurement of operating lease liabilities	16.8	12.1
Right-of-use assets obtained in exchange for operating lease liabilities	$ 36.2	$ 96.4
Weighted average remaining lease term (years)	11 years 6 months	11 years 3 months 18 days
Weighted average discount rate	4.00%	4.30%