Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($) |
Sep. 30, 2020 |
Mar. 31, 2020 |
|---|---|---|
| Amortized Cost | $ 65,470,282 | $ 69,933,553 |
| Gross Unrealized Holding Gains | 2,085,073 | 752,621 |
| Gross Unrealized Holding Losses | (91,432) | |
| Estimated Fair Value | 67,555,355 | 70,594,742 |
| Money Market Funds [Member] | ||
| Amortized Cost | 3,546,052 | 7,903,433 |
| Gross Unrealized Holding Gains | ||
| Gross Unrealized Holding Losses | ||
| Estimated Fair Value | 3,546,052 | 7,903,433 |
| Corporate Bond Securities [Member] | ||
| Amortized Cost | 61,924,230 | 62,030,120 |
| Gross Unrealized Holding Gains | 2,085,073 | 752,621 |
| Gross Unrealized Holding Losses | (91,432) | |
| Estimated Fair Value | $ 64,009,303 | $ 62,691,309 |