Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details Textual)

v3.8.0.1
Stock-Based Compensation (Details Textual)
 3 Months Ended
Jun. 01, 2015
shares
Mar. 31, 2018
USD ($)
$ / shares
shares
Mar. 31, 2018
GBP (£)
shares
Apr. 01, 2017
USD ($)
$ / shares
shares
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   6,625 6,625 6,375
Share-based compensation expenses under Director's plan | $   $ 365,000   $ 226,000
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   538,199    
Number of shares purchased by employees   8,110 8,110 6,627
Weighted average price | $ / shares   $ 45.79   $ 30.96
Share-based compensation expenses | $   $ 63,000   $ 34,000
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   361,438    
Restricted stock expense | $   $ 495,000   $ 697,000
Total unrecognized compensation | $   $ 6,908,000    
Recognized weighted average period (in years)   2 years 2 months 26 days 2 years 2 months 26 days  
Nonemployee Director Equity and Deferred Compensation Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares available for issuance   142,249