Accounting Policies - Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2017	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net (loss) income
Net (loss) income	$ 32.3	$ 31.5	$ 36.0	$ 28.2	$ (2.3)	$ 26.5	$ 27.2	$ 21.7	$ 128.0	$ 73.1	$ 84.2
Net (loss) income									$ 128.0	$ 73.1	$ 84.2
Shares (in shares)									34.3	34.4	34.4
Dilutive securities, principally common stock options (in shares)											0.1
Shares (in shares)									34.3	34.4	34.5
Per Share Amount
Per Share Amount (in dollars per share)	$ 0.94	$ 0.92	$ 1.05	$ 0.82	$ (0.07)	$ 0.77	$ 0.79	$ 0.63	$ 3.73	$ 2.12	$ 2.45
Dilutive securities, principally common stock options (in dollars per share)											(0.01)
Per Share Amount (in dollars per share)	$ 0.94	$ 0.92	$ 1.05	$ 0.82	$ (0.07)	$ 0.77	$ 0.79	$ 0.63	$ 3.73	$ 2.12	$ 2.44
Securities not included in the computation of diluted EPS
Options to purchase shares of Class A common stock, anti-dilutive											0.1
Shipping and Handling Costs
Shipping, Handling and Transportation Costs									$ 56.3	$ 52.1	$ 47.9
Research and Development Expense.
Research and Development Expense									$ 34.5	$ 29.0	$ 26.5