Note 4 - Marketable Securities - Securities in a Continuous Loss Position (Details) - USD ($)
|
Mar. 31, 2018 |
Mar. 31, 2017 |
| Fair market value, less than 12 months |
|
$ 33,503,369
|
| Gross unrealized losses, less than 12 months |
|
(247,149)
|
| Fair market value, greater than 12 months |
$ 9,072,719
|
|
| Gross unrealized losses, greater than 12 months |
|
|
| Total fair market value |
|
33,503,369
|
| Total gross unrealized losses |
|
(247,149)
|
| Corporate Bond Securities [Member] |
|
|
| Fair market value, less than 12 months |
61,731,248
|
32,198,766
|
| Gross unrealized losses, less than 12 months |
(1,003,849)
|
(246,935)
|
| Fair market value, greater than 12 months |
9,072,719
|
|
| Gross unrealized losses, greater than 12 months |
(245,511)
|
|
| Total fair market value |
70,803,967
|
32,198,766
|
| Total gross unrealized losses |
$ (1,249,360)
|
(246,935)
|
| Municipal Bonds [Member] |
|
|
| Fair market value, less than 12 months |
|
1,304,603
|
| Gross unrealized losses, less than 12 months |
|
(214)
|
| Fair market value, greater than 12 months |
|
|
| Gross unrealized losses, greater than 12 months |
|
|
| Total fair market value |
|
1,304,603
|
| Total gross unrealized losses |
|
$ (214)
|