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Note 2 - Summary of Significant Accounting Policies (Tables)
12 Months Ended
Dec. 31, 2021
Notes Tables  
Cash, Cash Equivalents and Investments [Table Text Block]
  

As of December 31,

 
  

2019

  

2018

 

Cash and cash equivalents

 $65,249,072  $100,652,809 

Restricted cash - short-term

  95,737,862   11,452,078 

Restricted cash - long-term

     68,292,023 

Cash, cash equivalents and restricted cash

 $160,986,934  $180,396,910 
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
  

Fair Value Measurements of Level 3 liability-classified warrant

 

Warrant liability at December 31, 2020

 $6,639,211 

Decrease in fair value of warrant liability

  (117,770)

Exercise of warrants

   

Warrant liability at December 31, 2021

 $6,521,441