Supplemental Information (Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of expenses in statements of operations
Research and development	$ 72.2	$ 73.6	$ 64.6
Advertising, promotions and marketing	42.5	45.0	41.0
Cooperative advertising expenditures	16.8	18.6	14.7
Rent expense	$ 58.5	$ 57.7	$ 57.9