Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Jun. 30, 2019	Mar. 31, 2019
Amortized Cost	$ 73,762,302	$ 74,223,159
Gross Unrealized Holding Gains	691,342	315,902
Gross Unrealized Holding Losses	(67,511)	(421,798)
Estimated Fair Value	61,611,878	74,117,263
Money Market Funds [Member]
Amortized Cost	12,774,255	6,703,809
Gross Unrealized Holding Gains
Gross Unrealized Holding Losses
Estimated Fair Value	12,774,255	6,703,809
Corporate Bond Securities [Member]
Amortized Cost	60,988,047	67,519,350
Gross Unrealized Holding Gains	691,342	315,902
Gross Unrealized Holding Losses	(67,511)	(421,798)
Estimated Fair Value	$ 61,611,878	$ 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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