Income Taxes - Summary of Income Tax Benefit or Expense and Effective Income Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
(Loss) before income taxes	$ (15.8)	$ (17.5)
Income tax (benefit)	$ (3.8)	$ (4.9)
Effective income tax rate	24.10%	28.00%