Leases - Maturities of Lease Liabilities (Details) $ in Millions	Dec. 31, 2020 USD ($)	Sep. 30, 2019 building
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	$ 12.8
2022	16.3
2023	14.2
2024	13.4
2025	11.1
Thereafter	37.9
Total lease payments	105.7
Less: imputed interest	(11.4)
Present value of operating lease liabilities	94.3
Finance Lease, Liability, Payment, Due [Abstract]
2021	2.9
2022	2.9
2023	2.7
2024	2.7
2025	2.6
Total lease payments	13.8
Less: imputed interest	(0.6)
Present value of financing lease liabilities	$ 13.2
Number of buildings | building		2
Lease term		5 years