Note 5 - Fair Value of Financial Instruments (Details Textual)	9 Months Ended
	Dec. 31, 2020
Available for Sale Debt Securitites, Percent of Total Assets	88.00%
Minimum [Member]
Available for Sale Debt Securities, Remaining Maturity (Week)	56 days
Maximum [Member]
Available for Sale Debt Securities, Remaining Maturity (Week)	3 years 60 days