Income Taxes - Summary of Income Tax Expense (Benefit) and Effective Income Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ 34.7	$ (2.7)	$ 27.6	$ (47.4)
Income tax expense (benefit)	$ 9.5	$ (0.3)	$ 8.1	$ (11.9)
Effective income tax rate	27.40%	11.10%	29.30%	(25.10%)