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Note 12 - Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2023
Notes Tables  
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Schedule [Table Text Block]

Grant Type

Vesting Schedule

Employee initial options grants

25% at one-year anniversary, 1/48 monthly thereafter

Employee recurring options grants

1/48 monthly

Non-employee consultant options grants

1/12 or 1/48 monthly

Employee RSUs

50% after one year, 50% after two years

Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
  

Year Ended December 31,

 
  

2023

  

2022

  

2021

 
  

(In thousands)

 

Continuing operations:

            

Research and development

 $4,754  $6,123  $6,791 

Selling, general and administrative

  7,140   8,042   8,154 

Total stock-based compensation in continuing operations

  11,894   14,165   14,945 

Discontinued operations

  (244)  (93)  2,685 

Total stock-based compensation

 $11,650  $14,072  $17,630 
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  

Year Ended December 31,

 
  

2023

  

2022

  

2021

 

Estimated weighted-average fair value

 $2.44  $2.94  $10.54 

Weighted-average assumptions:

            

Expected volatility

  93%  90%  81%

Expected life, in years

  7.2   6.0   6.0 

Risk-free interest rate

  3.97%  2.83%  1.06%

Expected dividend yield

  %  %  %
Share-Based Payment Arrangement, Activity [Table Text Block]
  

Options Outstanding

 Weighted- Average Exercise Price per Share 

Remaining Contractual Life (In years)

 

Aggregate Intrinsic Value (In thousands)

 

Balance at December 31, 2022

  13,872,973 $11.02       

Granted

  3,153,200  3.01       

Exercised

  (36,726) 4.10       

Forfeited

  (1,734,293) 9.96       

Balance at December 31, 2023

  15,255,154 $9.50  6.2 $1,388 

Vested and expected to vest at December 31, 2023

  14,762,090 $9.65  6.0 $1,272 

Exercisable at December 31, 2023

  10,554,140 $11.50  4.7 $217 
Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
  

RSUs Outstanding

 

Weighted- Average Grant Date Fair Value Per Share

 

Balance at December 31, 2022

  98,750 $7.53 

Vested and released

  (67,250) 7.53 

Forfeited

  (31,500) 7.53 

Balance at December 31, 2023

   $