Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Lessee, Lease, Description [Line Items]
Operating lease right-of-use asset	$ 7.4	$ 7.5
Operating lease liability, current	2.1	1.9
Operating lease, liability, noncurrent	6.1	6.6
Operating lease payments, due year one	2.4
Operating lease payments, due year two	2.3
Operating lease payments, due year three	2.3
Operating lease payments, due year four	0.9
Operating lease payments, due year five	0.2
Operating lease payments, due after year five	1.0
Operating lease payments, total due	9.1
Operating lease liability, undiscounted excess amount	(0.9)
Operating lease liability	8.2	8.5
Total operating lease expense	3.1	3.8	$ 3.7
Variable lease cost	$ 0.9	$ 0.9	$ 0.7
Operating lease, weighted average remaining lease term	4 years	4 years	5 years
Operating lease, weighted average discount rate, percent	4.80%	4.60%	4.30%
Operating lease payments	$ 2.4	$ 2.2	$ 3.0
Operating lease, right-of-use asset, Balance Sheet location	Other assets	Other assets
Operating lease liability, current, Balance Sheet location	Other current liabilities	Other current liabilities
Operating lease liability, non-current, Balance Sheet location	Other liabilities	Other liabilities
Operating lease liability, Balance Sheet location	Other Liabilities	Other Liabilities
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract	10 years