Note 5 - Fair Value of Financial Instruments (Tables)
 6 Months Ended
Sep. 30, 2020
Notes Tables  
Investments Classified by Contractual Maturity Date [Table Text Block]
Total
    
<1 Year
    
1–3 Years
    
3–5 Years
  
$
67,555,355
     $
26,778,033
     $
34,271,054
     $
6,506,268
  
Fair Value, Assets Measured on Recurring Basis [Table Text Block]
   
As of September 30, 2020
    
As of March 31, 2020
  
   
Level 1
    
Level 2
    
Total
    
Level 1
    
Level 2
    
Total
  
Money market funds
   $
3,546,052
     $
-
     $
3,546,052
     $
7,903,433
     $
-
     $
7,903,433
  
Corporate bonds
    
-
      
64,009,303
      
64,009,303
      
-
      
62,691,309
      
62,691,309
  
Total
   $
3,546,052
     $
64,009,303
     $
67,555,355
     $
7,903,433
     $
62,691,309
     $
70,594,742
  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
   
As of September 30, 2020
    
As of March 31, 2020
  
   

Amortized
Cost
    
Gross
Unrealized
Holding Gains
    
Gross
Unrealized
Holding Losses
    
Estimated
Fair
Value
    

Amortized
Cost
    
Gross
Unrealized
Holding Gains
    
Gross
Unrealized
Holding Losses
    
Estimated
Fair
Value
  
Money market funds
   $
3,546,052
     $
-
     $
-
     $
3,546,052
     $
7,903,433
     $
-
     $
-
     $
7,903,433
  
Corporate bonds
    
61,924,230
      
2,085,073
      
-
      
64,009,303
      
62,030,120
      
752,621
      
(91,432
)
    
62,691,309
  
Total
   $
65,470,282
     $
2,085,073
     $
-
     $
67,555,355
     $
69,933,553
     $
752,621
     $
(91,432
)
   $
70,594,742