Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments (Details 1)

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Fair Value of Financial Instruments (Details 1) - Fair Value, Measurement Frequency [Domain] - Fair Value Hierarchy [Domain] - USD ($)
$ in Thousands
 6 Months Ended
Jun. 27, 2015
Jun. 28, 2014
Summary of maturities of marketable securities    
Due in less than one year, adjusted cost $ 15,259  
Due after one year but within five years, adjusted cost 17,098  
Due after five years but within ten years, adjusted cost 4,673  
Due after ten years, adjusted cost 3,236  
Equity securities, adjusted cost 1,591  
Mutual Funds, adjusted cost 3,488  
Due in less than one year, fair value 15,128  
Due after one year but within five years, fair value 16,749  
Due after five years but within ten years, fair value 4,184  
Due after ten years, fair value 3,099  
Equity securities, fair value 1,411  
Mutual Funds, fair value 3,178  
Available-for-sale Debt Securities, Amortized Cost Basis 45,345  
Asset measured at, fair value $ 43,749  
Phantom Share Units (PSUs) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 3 years  
Fair Value Liability Recorded for Share Based Awards Related Expense $ 17 $ 21