Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details Textual)

v3.19.1
Stock-Based Compensation (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Mar. 30, 2019
Mar. 31, 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) 5,875 6,625
Share-based compensation expenses under Director's plan $ 285 $ 365
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 14,387 8,110
Weighted average price $ 28.37 $ 45.79
Share-based compensation expenses $ 255 $ 63
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 $ 811 $ 495
Equity Incentive Plan (2011 Plan) [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Total unrecognized compensation $ 8,708  
Recognized weighted average period (in years) 2 years 1 month 6 days