Schedule II (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Provision For Bad Debts [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	$ 0.4	$ 1.1	$ 1.3
Deductions	(0.1)	(0.7)	(0.2)
Balance at end of year	0.3	0.4	1.1
Provision For Discounts [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	1.3	0.8	2.0
Additions charged to earnings	17.6	16.9	15.8
Deductions	(17.4)	(16.4)	(17.0)
Balance at end of year	1.5	1.3	0.8
Provision For Warranties [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	0.2	0.3
Additions charged to earnings	3.2	8.0	1.6
Deductions	(3.3)	(8.1)	(1.3)
Balance at end of year	$ 0.1	$ 0.2	$ 0.3