Income Taxes - Summary of Income Tax Benefit or Expense and Effective Income Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income (loss) before income taxes	$ 8.6	$ (27.2)	$ (7.1)	$ (44.7)
Income tax expense (benefit)	$ 2.3	$ (6.7)	$ (1.4)	$ (11.6)
Effective income tax rate	26.70%	24.60%	19.70%	26.00%