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Note 8 - Stock Option Plan
9 Months Ended
Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]
8.     Stock option plan:

The following table presents stock option activity for the period:

    Three Months Ended
September 30,
   
Nine Months Ended
September 30,
 
   
2013
   
2014
   
2013
   
2014
 
                                 
Outstanding, beginning of period
    1,304,441       1,442,741       1,128,437       1,333,099  
Granted
    42,592       6,273       292,417       163,504  
Exercised
    (3,086 )     (1,028 )     (4,115 )     (1,800 )
Forfeited  and expired
    (876 )     (4,411 )     (73,668 )     (51,228 )
Outstanding, end of period
    1,343,071       1,443,575       1,343,071       1,443,575  
Exercisable, end of period
    898,894       1,078,009       898,894       1,078,009  

The fair value of each option issued to employees and non-employees is estimated using the Black-Scholes option-pricing model with the following weighted-average assumptions:

    Three Months Ended
September 30,
 
 
Nine Months Ended
September 30,
 
   
2013
   
2014
   
2013
   
2014
 
                                 
Average risk-free interest rate
    1.82 %     1.95 %     1.03 %     1.97 %
Average expected term (in years)
    6.00       6.25       6.20       6.20  
Expected volatility
    70 %     74 %     70 %     74 %
Expected dividend yield
    0.00 %     0.00 %     0.00 %     0.00 %
Estimated forfeiture rate
    0.00 %     0.00 %     0.00 %     0.00 %