Leases - Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Leases
Operating lease expense	$ 4.9	$ 4.8	$ 9.8	$ 9.4
Finance lease expense Amortization of right-of-use asset	0.7		0.8
Finance lease expense Interest on lease liabilities	0.1		0.1
Short-term lease expense	0.1	0.1	0.1	0.1
Variable lease expense	0.5	0.7	1.4	1.8
Total lease expense	$ 6.3	$ 5.6	$ 12.2	$ 11.3