Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Sep. 30, 2019	Mar. 31, 2019
Amortized Cost	$ 71,753,787	$ 74,223,159
Gross Unrealized Holding Gains	878,961	315,902
Gross Unrealized Holding Losses	(26,360)	(421,798)
Estimated Fair Value	72,606,388	74,117,263
Money Market Funds [Member]
Amortized Cost	13,807,888	6,703,809
Gross Unrealized Holding Gains
Gross Unrealized Holding Losses
Estimated Fair Value	13,807,888	6,703,809
Corporate Bond Securities [Member]
Amortized Cost	57,945,899	67,519,350
Gross Unrealized Holding Gains	878,961	315,902
Gross Unrealized Holding Losses	(26,360)	(421,798)
Estimated Fair Value	$ 58,798,500	$ 67,413,454

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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