Allowance for Doubtful Accounts - Allowance for Bad Debts (Details) $ in Millions	3 Months Ended
	Dec. 31, 2020 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	1.5
Allowance charge-offs	0.0
Balance as of December 31, 2020	36.8
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