Cash Equivalents and Investments (Available for sales securities) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Apr. 01, 2016	Dec. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		$ 171.7		$ 133.3
Cash Equivalents		29.9		22.2
Short-term investments		141.8		111.1
Available-for-sale Debt Securities, Amortized Cost		171.7		133.3
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Securities		0.1	$ 0.0
Available-for-sale Securities, Gross Realized Gain (Loss)		0.0
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	9.6		11.7
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	10.0		10.0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	65.9		31.7
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	$ 83.8		$ 77.5

[1] The Company’s available-for sale securities are valued using readily available pricing sources for comparable instruments, or model-driven valuations using significant inputs derived from or corroborated by observable market data, including yield curves and credit ratings.