Note 5 - Marketable Securities (Tables)
 9 Months Ended
Dec. 31, 2016
Notes Tables  
Marketable Securities [Table Text Block]
Total
 
 
<1 Year
 
 
1–3 Years
 
 
3–5 Years
 
$ 84,323,941     $
24,655,206
     $
36,400,319
     $
23,268,416
  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
 
 
As of December 31, 2016
 
 
As of March 31, 2016
 
 
 

Adjusted
Cost
 
 
Gross
Unrealized
Gains
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
 

Adjusted
Cost
 
 
Gross
Unrealized
Gains
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
Corporate bonds
   $
83,222,388
     $
123,045
     $
(334,944
)
   $
83,010,489
     $
83,339,487
     $
717,206
     $
(10,824
)
   $
84,045,869
  
Municipal bonds
   
1,314,695
      
-
      
(1,243
)
    
1,313,452
      
1,344,328
      
2,522
      
-
      
1,346,850
  
Total
   $
84,537,083
     $
123,045
     $
(336,187
)
   $
84,323,941
     $
84,683,815
     $
719,728
     $
(10,824
)
   $
85,392,719
  
Schedule of Unrealized Loss on Investments [Table Text Block]
 
 
Less Than 12 Months
 
 
12 Months or Greater
 
 
Total
 
 
 
Fair
Market
Value
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
 
Gross
Unrealized
Losses
 
As of December 31, 2016                                                
Corporate bonds
   $
30,147,097
     $
(334,944
)
   $
-
     $
-
     $
30,147,097
     $
(334,944
)
Municipal bonds
   
1,313,452
      
(1,243
)
    
-
  
 
 
-
 
    
1,313,452
      
(1,243
)
Total
   $
31,460,549
     $
(336,187
)
   $
-
     $
-
     $
31,460,549
     $
(336,187
)
As of March 31, 2016                                                
Corporate bonds
   $
3,003,606
     $
(6,703
)
   $
2,599,870
     $
(4,121
)
   $
5,603,476
     $
(10,824
)
Municipal bonds
   
-
      
-
      
-
      
-
      
-
      
-
  
Total
   $
3,003,606
     $
(6,703
)
   $
2,599,870
     $
(4,121
)
   $
5,603,476
     $
(10,824
)