Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($) |
Sep. 30, 2018 |
Mar. 31, 2018 |
|---|---|---|
| Amortized Cost | $ 77,897,062 | $ 78,804,359 |
| Gross Unrealized Holding Gains | ||
| Gross Unrealized Holding Losses | (1,320,776) | (1,249,360) |
| Estimated Fair Value | 76,576,286 | 77,554,999 |
| Money Market Funds [Member] | ||
| Amortized Cost | 5,774,385 | 3,951,032 |
| Gross Unrealized Holding Gains | ||
| Gross Unrealized Holding Losses | ||
| Estimated Fair Value | 5,774,385 | 3,951,032 |
| Corporate Bond Securities [Member] | ||
| Amortized Cost | 72,122,677 | 74,853,327 |
| Gross Unrealized Holding Gains | ||
| Gross Unrealized Holding Losses | (1,320,776) | (1,249,360) |
| Estimated Fair Value | $ 70,801,901 | $ 73,603,967 |