Schedule II - Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts:
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 5.9	$ 6.0	$ 5.7
Charged to Costs and Expenses	2.1	2.0	4.2
Deductions	(1.8)	(2.1)	(3.9)
Balance at End of Period	6.2	5.9	6.0
Reserve for sales returns:
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	6.8	4.9	5.1
Charged to Costs and Expenses	40.6	38.1	34.4
Deductions	(41.0)	(36.2)	(34.6)
Balance at End of Period	$ 6.4	$ 6.8	$ 4.9