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Note 13 - Stock Option Plan and Non-Employee Director Compensation Plan (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Allocated share-based compensation expense $ 90,000 $ 70,000 $ 71,000  
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized $ 154,000      
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition 50 months      
Share-based compensation arrangement by share-based payment award, options, grants in period, gross 35,000 29,350 25,000  
Share-based compensation arrangement by share-based payment award, options, forfeitures in period 22,600 34,150 8,575  
Share-based compensation arrangement by share-based payment award, options, exercises in period     19,025  
Share-based compensation arrangement by share-based payment award, options, outstanding, number 121,550 109,150 113,950 116,550
Non-Employee [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, number of shares authorized 50,000      
Share-based compensation arrangement by share-based payment award, shares issued 1,740      
Stock repurchase program remaining number of shares 48,260      
Annual stock based compensation service fee $ 8,000,000      
Semi annual stock based compensation payment $ 4,000,000      
The 2015 Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, number of shares authorized 300,000      
Share-based compensation arrangement by share-based payment award, options, grants in period, gross 212,550      
Share-based compensation arrangement by share-based payment award, options, forfeitures in period 70,175      
Share-based compensation arrangement by share-based payment award, options, exercises in period 20,825      
Share-based compensation arrangement by share-based payment award, options, outstanding, number 121,550      
Director Compensation Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Allocated share-based compensation expense $ 80,000      
Employee Stock Option | The 2015 Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, period options can be exercised after grant date 6 months      
Employee Stock Option | The 2015 Plan [Member] | First Anniversary [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage 20.00%      
Employee Stock Option | The 2015 Plan [Member] | Maximum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, expiration period 10 years