Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Other Expenses [Abstract]
Non-income taxes	$ 13.5	$ 14.8	$ 6.6
Insurance	10.8	7.1	4.7
Employee related expenses	9.6	7.0	4.7
Other direct business expenses	10.0	6.3	4.6
Membership fees	3.3	2.8	2.4
Director and public company expenses	1.8	1.5	1.4
Office expenses	1.7	1.3	1.8
Other expenses	9.9	5.5	3.4
Total other expenses	$ 60.6	$ 46.3	$ 29.6