Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details Textual)

v3.19.2
Stock-Based Compensation (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Jun. 29, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Ratio for additional common stock shares issued, under ESPP 16.67%  
2012 Nonemployee Director Fees Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Award of shares granted (in shares) 12,500 12,500
Share-based compensation expenses under Director's plan $ 582 $ 660
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%  
Employee Stock Purchase Plan and U.K. Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Number of shares purchased by employees 25,481 18,728
Weighted average price $ 33.09 $ 43.24
Share-based compensation expenses $ 329 $ 138
Time Based [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Vesting period 3 years  
Performance Based [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Vesting period 3 years  
Restricted Stock and Restricted Stock Units [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Compensation expense $ 1,859 $ 1,279
Total unrecognized compensation $ 7,806  
Recognized weighted average period (in years) 1 year 10 months 24 days