Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details Textual)

v3.20.2
Stock-Based Compensation (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
9 Months Ended
Sep. 26, 2020
Sep. 28, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Recognized weighted average period (in years) 2 years 6 months  
Contractual term of stock options 10 years  
Unrecognized compensation cost related to the stock options $ 147  
Award of shares granted (in shares) 182,000  
Stock-based compensation expense $ 3,830 $ 4,058
2012 Nonemployee Director Fees Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Award of shares granted (in shares) 11,775 18,875
Stock-based compensation expense $ 480 $ 856
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 33,519 37,217
Weighted average price $ 30.65 $ 33.65
Share-based compensation expenses $ 220 $ 398
Ratio for additional common stock shares issued, under ESPP 6  
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  
RSUs [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Target amount percentage 0.00%  
RSUs [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Target amount percentage 200.00%  
Restricted Stock and Restricted Stock Units [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Compensation expense $ 3,158 $ 2,783
Total unrecognized compensation $ 6,426  
Recognized weighted average period (in years) 1 year 10 months 24 days