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Note 8 - Share-based Compensation - Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Balance, number of shares (in shares) 2,182,708  
Balance, weighted average exercise price (in dollars per share) $ 4.04  
Balance, weighted average remaining contractual term (Year) 6 years 8 months 12 days 7 years 6 months
Balance, aggregate intrinsic value $ 0 $ 343
Stock options granted, number of shares (in shares) 543,513  
Stock options granted, weighted average exercise price (in dollars per share) $ 1.69  
Stock options exercised, number of shares (in shares) (199)  
Stock options exercised, weighted average exercise price (in dollars per share) $ 1.49  
Stock options forfeited, number of shares (in shares) (275,662)  
Stock options forfeited, weighted average exercise price (in dollars per share) $ 2.15  
Stock options expired, number of shares (in shares) (6,349)  
Stock options expired, weighted average exercise price (in dollars per share) $ 16.09  
Balance, number of shares (in shares) 2,444,011 2,182,708
Balance, weighted average exercise price (in dollars per share) $ 3.70 $ 4.04
Exercisable, number of shares (in shares) 1,558,484  
Exercisable, weighted average exercise price (in dollars per share) $ 4.61  
Exercisable, weighted average remaining contractual term (Year) 5 years 6 months  
Exercisable, aggregate intrinsic value $ 0