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Note 9 - Income Taxes (Tables)
12 Months Ended
Dec. 31, 2023
Notes Tables  
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
  

Year ended December 31,

 
  

2023

  

2022

  

2021

 

Tax at federal statutory rate

  21%  21%  21%

State tax, net of federal benefit

         

Share-based compensation

  0.2   (0.5)  1.2 

Research and development credits

  5.1   4.9   2.3 

Section 162(m) limitation

     (0.2)  (0.5)

Other

  (2.3)  (1.8)  (0.2)

Change in valuation allowance

  (24.0)  (23.4)  (23.8)

Effective income tax rate

  %  %  %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
  

December 31,

 
  

2023

  

2022

 

Deferred tax assets:

        

Net operating loss carryforwards

 $33,322  $28,017 

Share-based compensation

  2,561   2,706 

Research and development credit carryforwards

  12,557   9,681 

Capitalized research and development expenses

  27,538   12,690 

Other

  1,371   934 

Total deferred tax assets

  77,349   54,028 

Valuation allowance

  (77,349)  (54,002)

Net deferred tax assets

     26 

Deferred tax liabilities:

        

Operating lease right-of-use assets

     (26)

Total deferred tax liabilities

     (26)

Net deferred tax asset (liability)

 $  $ 
Summary of Income Tax Contingencies [Table Text Block]
  

Year ended December 31,

 
  

2023

  

2022

  

2021

 

Beginning balance

 $6,496  $5,001  $4,500 

Expired research and development tax credits

 $(50) $  $ 

Additions based on tax positions related to the current year

  1,967   1,495   501 

Ending balance

 $8,413  $6,496  $5,001