Stockholders' Equity - Changes in Accumulated Other Comprehensive Income by Component, Net of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2017	Jan. 03, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at year-end	$ 58.7	$ 60.7
Other comprehensive income (loss) before reclassifications	72.0	(2.0)
Amounts reclassified from accumulated other comprehensive income	0.1	0.0
Other comprehensive income (loss)	72.1	(2.0)	$ 9.6	[1]
Balance at year-end	130.8	58.7	60.7
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at year-end	(23.3)	(22.6)
Other comprehensive income (loss) before reclassifications	16.4	(0.6)
Amounts reclassified from accumulated other comprehensive income	0.0	(0.1)
Other comprehensive income (loss)	16.4	(0.7)
Balance at year-end	(6.9)	(23.3)	(22.6)
Unrealized Gains and Losses on Investment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at year-end	83.8	84.9
Other comprehensive income (loss) before reclassifications	56.2	(1.1)
Amounts reclassified from accumulated other comprehensive income	0.0	0.0
Other comprehensive income (loss)	56.2	(1.1)
Balance at year-end	140.0	83.8	84.9
Pension Liability Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at year-end	(1.8)	(1.6)
Other comprehensive income (loss) before reclassifications	(0.6)	(0.3)
Amounts reclassified from accumulated other comprehensive income	0.1	0.1
Other comprehensive income (loss)	(0.5)	(0.2)
Balance at year-end	$ (2.3)	$ (1.8)	$ (1.6)

[1] Fiscal year included 53 weeks.