Income Taxes- Summary of Income Tax Benefit and Effective Income Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
(Loss) before income taxes	$ (27.2)	$ (4.9)	$ (44.7)	$ (16.9)
Income tax (benefit)	$ (6.7)	$ (1.3)	$ (11.6)	$ (4.5)
Effective income tax rate	24.60%	26.50%	26.00%	26.60%