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Note 13 - Stock-based Compensation (Tables)
12 Months Ended
Dec. 31, 2022
Notes Tables  
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
   

Number of

Shares

   

Weighted-

Average Exercise

Price

   

Weighted-Average

Remaining

Contractual Term

(Years)

 

Balance at December 31, 2021

    4,640,660     $ 6.64       5.66  

Granted

    3,153,881       0.70          

Forfeited

    (129,134 )     1.60          

Cancelled

    (36,987 )     21.11          

Exercised

    (43,453 )     0.41          

Balance at December 31, 2022

    7,584,967     $ 4.22       5.31  
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested and Expected to Vest, Exercisable [Table Text Block]
   

Number of

Shares

   

Weighted-

Average Exercise

Price

   

Weighted-Average

Remaining

Contractual Term

(Years)

   

Aggregate

Intrinsic Value

(Millions)

 

Exercisable at December 31, 2022

    3,524,473     $ 7.40       4.75     $ -  

Vested or expected to vest at December 31, 2022

    7,350,141     $ 4.32       5.28     $ -  
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
  Years Ended December 31,
  2022  2021

Expected dividend yield

 0%  0%

Expected volatility

 126%-133%  118%-139%

Risk-free interest rate

 1.25%-4.40%  0.33%-1.11%

Expected life (in years)

 3.8-4.5  3.8-4.5 
Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
   

Number of

Restricted

Stock Units

Outstanding

   

Weighted-

Average Grant

Date Fair

Value

 

Unvested December 31, 2021

    3,839,030     $ 2.36  

Granted

    6,996,822       0.71  

Vested

    (2,076,663 )     2.34  

Forfeited

    (275,698 )     1.19  

Unvested December 31, 2022

    8,483,491     $ 1.04  
Share-Based Payment Arrangement, Cost by Plan [Table Text Block]
   

Years Ended December 31,

 
   

2022

   

2021

 
   

(in thousands)

 

Stock options

  $ 3,654     $ 4,535  

Restricted stock units

    3,319       3,954  

Performance restricted stock units

    1,443       940  
    $ 8,416     $ 9,429