Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax expense	$ 0.2	$ 1.5	$ 8.9	$ 6.0
Effective income tax rate, percent	1.90%	17.90%	19.30%	20.30%
Deferred Tax Assets, Net Of Deferred Tax Liabilities	$ 3.2		$ 3.2		$ 20.7
Valuation allowance, deferred tax asset, amount	3.3		3.3		$ 3.3
Unrecognized Tax Benefits, Period Increase (Decrease)	1.6
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	2.3		2.3
Deferred Tax Liabilities, Other	$ 0.1		$ 0.1