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Fair Value Measurements (Schedule of Marketable Securities) (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 29, 2017
Dec. 29, 2016
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 37.1 $ 45.8
Aggregate Fair Value - Short term marketable securities 18.8 26.1
Aggregate Fair Value - Long term marketable securities 18.2 19.6
Aggregate Fair Value - Total marketable securities 37.0 45.7
Short-term Marketable Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 18.8 26.1
Aggregate Fair Value - Short term marketable securities 18.8 26.1
Short-term Marketable Securities [Member] | U.S. Government Treasury Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 1.2 1.2
Aggregate Fair Value - Short term marketable securities $ 1.2 $ 1.2
Maturities [1] 3 months 19 days 9 months 18 days
Short-term Marketable Securities [Member] | Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 0.3 $ 2.9
Aggregate Fair Value - Short term marketable securities 0.3 $ 2.9
Maturities [1]   7 months 6 days
Short-term Marketable Securities [Member] | U.S. Government Agency Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 1.0 $ 1.0
Aggregate Fair Value - Short term marketable securities 1.0 $ 1.0
Maturities [1]   6 months
Short-term Marketable Securities [Member] | Commercial Paper, Financial [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 6.6  
Aggregate Fair Value - Short term marketable securities $ 6.6  
Maturities [1] 1 month 6 days  
Short-term Marketable Securities [Member] | Commercial Paper, Industrial [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 7.3  
Aggregate Fair Value - Short term marketable securities $ 7.3  
Maturities [1] 1 month 6 days  
Short-term Marketable Securities [Member] | Certificates Of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 2.4  
Aggregate Fair Value - Short term marketable securities $ 2.4  
Maturities [1] 3 months 19 days  
Short-term Marketable Securities [Member] | Commercial Paper [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis   $ 13.0
Aggregate Fair Value - Short term marketable securities   $ 13.0
Maturities [1]   1 month 6 days
Short-term Marketable Securities [Member] | Financial Certificate Of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis   $ 7.7
Aggregate Fair Value - Short term marketable securities   $ 7.7
Maturities [1]   7 months 6 days
Short-term Marketable Securities [Member] | Industrial Certificates Of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis   $ 0.3
Aggregate Fair Value - Short term marketable securities   $ 0.3
Maturities [1]   10 months 24 days
Long-term Marketable Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 18.3 $ 19.7
Aggregate Fair Value - Long term marketable securities 18.2 19.6
Long-term Marketable Securities [Member] | Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 1.9 1.9
Aggregate Fair Value - Long term marketable securities $ 1.9 $ 1.8
Maturities [1] 2 years 7 months 6 days 2 years 8 months 12 days
Long-term Marketable Securities [Member] | U.S. Government Agency Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 14.2 $ 15.6
Aggregate Fair Value - Long term marketable securities $ 14.1 $ 15.5
Maturities [1] 2 years 10 months 25 days 3 years 6 months
Long-term Marketable Securities [Member] | Certificates Of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis   $ 2.2
Aggregate Fair Value - Long term marketable securities   $ 2.3
Maturities [1]   2 years 7 months 6 days
Long-term Marketable Securities [Member] | Financial Certificate Of Deposit [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis $ 2.2  
Aggregate Fair Value - Long term marketable securities $ 2.2  
Maturities [1] 2 years 1 month 6 days  
[1] Maturities—Securities available for sale include obligations with various contractual maturity dates some of which are greater than one year. The Company considers the securities to be liquid and convertible to cash within 30 days.