Note 5 - Fair Value of Financial Instruments (Details Textual)	3 Months Ended
	Jun. 30, 2020
Available for Sale Debt Securitites, Percent of Total Assets	89.00%
Minimum [Member]
Available for Sale Debt Securities, Remaining Maturity (Month)	120 days
Maximum [Member]
Available for Sale Debt Securities, Remaining Maturity (Month)	3 years 240 days