Note 5 - Fair Value of Financial Instruments (Details Textual) |
3 Months Ended |
|---|---|
Jun. 30, 2021 | |
| Available for Sale Debt Securitites, Percent of Total Assets | 87.00% |
| Number of Other-than-temporarily Impaired Available-for-sale Securities | 0 |
| Number of Other-than-temporarily Impaired Marketable Securities | 0 |
| Minimum [Member] | |
| Available for Sale Debt Securities, Remaining Maturity (Week) | 42 days |
| Maximum [Member] | |
| Available for Sale Debt Securities, Remaining Maturity (Week) | 44 months |