Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Expenses [Abstract]
Accretion Expense	$ 0.2	$ 0.0	$ 0.3	$ 0.0
Insurance	1.1	0.9	3.1	2.6
Advertising, meetings, and conferences	0.5	1.2	6.1	4.1
Office supplies and printing	0.6	0.5	1.5	1.5
Other clearing related expenses	0.8	0.7	2.2	1.8
Other non-income taxes	1.2	1.1	3.8	3.2
Other	3.2	2.7	8.7	7.8
Total other expenses	$ 7.6	$ 7.1	$ 25.7	$ 21.0