Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Details Textual)

v3.8.0.1
Stock-Based Compensation (Details Textual)
 12 Months Ended
Jun. 01, 2015
shares
Dec. 30, 2017
USD ($)
$ / shares
shares
Dec. 30, 2017
GBP (£)
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Jan. 02, 2016
USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Ratio for additional common stock shares issued, under ESPP   16.67% 16.67%    
2012 Director Equity Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Aggregate number of shares authorized for grant   270,000      
Common stock shares for each nonemployee director 250        
Fee for the chairs of each Board committee 150.00%        
Annual retainer of common stock received by non employee directors   2,000 2,000    
Stock option granted, shares   26,000 26,000 24,500  
Share-based compensation expenses under Director's plan | $   $ 1,240,000   $ 831,000 $ 829,000
Employee Stock Purchase Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Rate of common stock at market value   85.00% 85.00%    
Employee Stock Purchase Plan and U.K. Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Aggregate number of shares authorized for grant   1,096,875      
Shares available for issuance   546,309      
Number of shares purchased by employees   31,983 31,983 33,956  
Weighted average price | $ / shares   $ 36.20   $ 25.95  
Share-based compensation expenses | $   $ 429,000   $ 312,000 199,000
Minimum [Member] | Employee Stock Purchase Plan and U.K. Plan [Member] | United States [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares allowed to be purchased by employees | $   $ 25,000      
Minimum [Member] | Employee Stock Purchase Plan and U.K. Plan [Member] | United Kingdom [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares allowed to be purchased by employees | £     £ 1,500    
Allowable employees purchase rate of common stock based on annual salary   10.00% 10.00%    
Maximum [Member] | 2012 Director Equity Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Maximum number of share issuable to non employee directors per year   35,000      
Equity Incentive Plan (2011 Plan) [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Aggregate number of shares authorized for grant   1,000,000      
Shares available for issuance   457,567      
Restricted stock expense | $   $ 2,376,000   $ 3,676,000 $ 3,254,000
Total unrecognized compensation | $   $ 1,988,000      
Recognized weighted average period (in years)   1 year 4 months 6 days 1 year 4 months 6 days    
Nonemployee Director Equity and Deferred Compensation Plan [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares available for issuance   148,874