Note 5 - Marketable Securities (Tables)
 6 Months Ended
Sep. 30, 2015
Notes Tables  
Marketable Securities [Table Text Block]
 
Total
 
 
<1 Year
 
 
1–3 Years
 
 
3–5 Years
 
  $ 83,956,776     $ 23,175,666     $ 39,590,273     $ 21,190,837  
Schedule of Available-for-sale Securities Reconciliation [Table Text Block]
 
 
As of September 30, 2015
 
 
As of March 31, 2015
 
 
 

Adjusted
Cost
 
 
Gross
Unrealized
Gains
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
 

Adjusted
Cost
 
 
Gross
Unrealized
Gains
 
 
Gross
Unrealized
Losses
 
 
Fair
Market
Value
 
Corporate bonds
   $ 81,960,402     $ 645,841     $ (17,615
)
   $ 82,588,628     $ 88,456,886     $ 1,185,469     $ (16,371
)
   $ 89,625,984  
Municipal bonds
    1,364,084       4,064       -       1,368,148       1,383,839       3,272       -       1,387,111  
Total
   $ 83,324,486     $ 649,905     $ (17,615
)
   $ 83,956,776     $ 89,840,725     $ 1,188,741     $ (16,371
)
   $ 91,013,095  
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 September 30, 2015                                                
Corporate bonds
   $ 8,834,101     $ (9,840
)
   $ 2,597,444     $ (7,775
)
   $ 11,431,545     $ (17,615
)
Municipal bonds
    -       -       -       -       -       -  
Total
   $ 8,834,101     $ (9,840
)
   $ 2,595,544     $ (7,775
)
   $ 11,431,545     $ (17,615
)
As of March 31, 2015                                                
Corporate bonds
   $ 3,015,900     $ (163
)
   $ 2,590,240     $ (16,208
)
   $ 5,606,140     $ (16,371
)
Municipal bonds
    -       -       -       -       -       -  
Total
   $ 3,015,900     $ (163
)
   $ 2,590,240     $ (16,208
)
   $ 5,606,140     $ (16,371
)