Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2015	Jun. 29, 2014	Jun. 28, 2015	Jun. 29, 2014	Dec. 28, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain on available-for-sale investments, net of tax	$ 3.5	$ 10.6	$ 6.6	$ 10.5
Cost of available-for-sale investments	16.7		16.7		$ 17.2
Temp Holdings Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain on available-for-sale investments, net of tax	$ 3.5	$ 10.6	$ 6.6	$ 10.5