Leases - Narrative (Details) $ in Millions	12 Months Ended
	Sep. 30, 2021 USD ($) renewal_option	Sep. 30, 2020 USD ($)	Oct. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of options to renew (or more) | renewal_option	1
Termination period	2 years
Operating right of use assets	$ 125.3	$ 101.5	$ 33.1
Operating lease liabilities	$ 146.6	$ 118.7	$ 36.2
Building | Minimum
Lessee, Lease, Description [Line Items]
Renewal term	3 years
Building | Maximum
Lessee, Lease, Description [Line Items]
Renewal term	10 years