Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Other Expenses [Abstract]
Non-income taxes	$ 2.5	$ 4.7
Insurance	2.9	2.7
Employee related expenses	1.9	3.6
Other direct business expenses	4.4	4.0
Membership fees	0.9	0.8
Director and public company expenses	0.5	0.5
Office expenses	0.6	0.4
Other expenses	3.2	2.7
Total other expenses	$ 16.9	$ 19.4