Allowance for Doubtful Accounts - Allowance for Bad Debts (Details) $ in Millions	9 Months Ended
	Jun. 30, 2021 USD ($)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	$ 27.1
Provision for bad debts	3.7
Allowance charge-offs	(6.4)
Balance as of June 30, 2021	32.6
Cumulative Effect, Period of Adoption, Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	8.2
Cumulative Effect, Period of Adoption, Adjusted Balance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	$ 35.3