Income Taxes - Summary of Income Tax Benefit and Effective Income Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
(Loss) before income taxes	$ (17.4)	$ (15.8)
Income tax benefit	$ 4.6	$ 3.8
Effective income tax rate	26.40%	24.10%