Note 5 - Fair Value of Financial Instruments (Details Textual) |
9 Months Ended |
|---|---|
Dec. 31, 2018 | |
| Available for Sale Debt Securitites, Percent of Total Assets | 89.00% |
| 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 | 14 days |
| Maximum [Member] | |
| Available for Sale Debt Securities, Remaining Maturity | 4 years 210 days |