Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Sep. 30, 2021	Mar. 31, 2021
Amortized Cost	$ 59,606,100	$ 63,451,301
Gross Unrealized Holding Gains	1,152,671	1,570,195
Gross Unrealized Holding Losses	(110,789)	(160,674)
Estimated Fair Value	60,647,982	64,860,822
Money Market Funds [Member]
Amortized Cost	10,442,555	10,143,196
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	10,442,555	10,143,196
Corporate Bond Securities [Member]
Amortized Cost	49,163,545	53,308,105
Gross Unrealized Holding Gains	1,152,671	1,570,195
Gross Unrealized Holding Losses	(110,789)	(160,674)
Estimated Fair Value	$ 50,205,427	$ 54,717,626

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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