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Note I - Stock-based Compensation Plans (Tables)
 3 Months Ended
Jul. 31, 2017
Notes Tables  
Stock Option Plan Comparison [Table Text Block]
    Restated
Option Plan
     
Minimum exercise price as a percentage of fair market value at date of grant    
100
 %
Last expiration date for outstanding options    
May 1, 2027
  
Shares available for grant at July 31, 2017    
284,000
  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
    Three Months Ended
July 31,
    2017   2016
Expected term (years)    
5.5
      
5.5
  
Risk-free interest rate    
1.81
 %    
1.32
 %
Volatility    
36
 %    
36
 %
Dividend yield    
-
      
-
  
Schedule of Share-based Compensation, Stock Options, Exercises [Table Text Block]
    Three Months Ended
July 31,
(Dollars in thousands)   2017   2016
         
Options exercised    
35,250
      
3,750
  
Cash received from option exercises   $
543
     $
77
  
Intrinsic value of options exercised   $
784
     $
14