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Note 6 - Stockholders' Equity and Stock-based Compensation (Tables)
9 Months Ended
Sep. 30, 2025
Notes Tables  
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Cost of product revenue

 $52  $  $52  $ 

Research and development

  2,232   1,108   7,329   3,058 

Selling, general and administrative

  3,333   1,874   9,106   3,735 

Total stock-based compensation expense

 $5,617  $2,982  $16,487  $6,793 
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Time-based options

 $3,937  $2,131  $11,623  $4,609 

Performance-based options

     5      27 

Market-based options

  1,577   788   4,581   1,978 

ESPP

  103   58   283   179 

Total stock-based compensation expense

 $5,617  $2,982  $16,487  $6,793 
The 2015 Plan, 2017 Plan and Inducement Plan [Member]  
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
  

Stock Options Outstanding

 
  

Number of shares

  

Weighted average exercise price

  Weighted average remaining life (in years) 

Balances — December 31, 2024

  10,979,332  $9.59   7.11 

Options granted

  2,884,343   18.67     

Options exercised

  (493,431)  4.26     

Options canceled

  (66,500)  13.13     

Options expired

          

Balances — September 30, 2025

  13,303,744  $11.74   7.24 

Exercisable — September 30, 2025

  4,806,075  $13.44   5.20 
The 2017 Employee Stock Purchase Plan [Member]  
Notes Tables  
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Expected term in years

  0.5 - 1.0   0.5 - 1.0   0.5 - 1.0   0.5 - 1.0 

Expected volatility

  98%   98%   98%   98% 

Risk-free interest rate

  3.8% - 4.0%   4.4% - 5.3%   3.8% - 4.3%   4.9% - 5.3% 

Dividend yield

            
Share-Based Payment Arrangement, Option [Member]  
Notes Tables  
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Expected term in years

  5.2 - 6.3   5.0 - 6.3   5.0 - 6.9   5.0 - 6.3 

Expected volatility

  93% - 95%   93% - 97%   93% - 100%   91% - 97% 

Risk-free interest rate

  4.0% - 4.1%   4.5%   4.0% - 4.6%   4.0% - 4.5% 

Dividend yield

            
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Expected term in years

  2.2 - 4.5   2.2 - 4.2   2.2 - 7.0   2.2 - 5.8 

Expected volatility

  

90%

   

90%

   

90%

   

90%

 

Risk-free interest rate

  

3.9%

   

3.9%

   

3.9% - 4.6%

   

3.9% - 4.4%

 

Dividend yield

            
  

Three Months Ended

September 30,

  

Nine Months Ended

September 30,

 
  

2025

  

2024

  

2025

  

2024

 

Expected term in years

        6.1 - 8.9    

Expected volatility

        

90%

    

Risk-free interest rate

        

4.4% - 4.6%

    

Dividend yield