Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts:
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Year	$ 4.4	$ 4.0	$ 3.6
Charged to Expense	2.5	2.1	3.0
Deductions	(2.5)	(1.7)	(2.6)
Balance End of Year	4.9	4.4	4.0
Allowance for doubtful accounts: | Change in Accounting Standard
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Year	0.5	0.0	0.0
Balance End of Year		0.5	0.0
Deferred income tax asset valuation allowance:
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance Beginning of Year	0.2	0.2	0.2
Additions	1.2	0.0	0.0
Deductions	0.0	0.0	0.0
Balance End of Year	$ 1.4	$ 0.2	$ 0.2