Supplemental Information (Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of expenses in statements of operations
Research and development	$ 66.8	$ 69.9	$ 72.2
Advertising, promotions and marketing	26.5	43.7	42.5
Cooperative advertising expenditures	$ 22.2	$ 21.3	$ 16.8