Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Oct. 01, 2019
Lessee, Lease, Description [Line Items]
Operating lease right-of-use asset	$ 11.9
Operating lease liability, current	2.2	$ 0.0
Operating lease, liability, noncurrent	11.0
Operating lease payments, due remainder of fiscal year	2.9
Operating lease payments, due year two	2.8
Operating lease payments, due year three	2.5
Operating lease payments, due year four	1.9
Operating lease payments, due year five	2.0
Operating lease payments, due after year five	2.8
Operating lease payments, total due	14.9
Operating lease liability, undiscounted excess amount	(1.7)
Operating lease liability	13.2
Operating lease payments, due remainder of fiscal year		2.7
Operating lease payments, due year two		2.7
Operating lease payments, due year three		2.7
Operating lease payments, due year four		2.7
Operating lease payments, due year five		1.9
Operating lease payments, due after year five		4.7
Operating lease payments, total due		17.4
Operating lease expense	4.0
Operating lease, rent expense		$ 3.3	$ 2.1
Operating lease payments	$ 3.6
Operating lease, weighted average discount rate, percent	4.20%
Operating lease, right-of-use asset, Balance Sheet location	us-gaap:OtherAssets
Operating lease liability, current, Balance Sheet location	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease liability, non-current, Balance Sheet location	us-gaap:OtherLiabilitiesNoncurrent
Operating lease liability, Balance Sheet location	us-gaap:OtherLiabilities
Operating lease, weighted average remaining lease term	6 years
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	7 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease right-of-use asset				$ 14.8
Operating lease liability				$ 16.0