Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Sep. 30, 2020	Mar. 31, 2020
Amortized Cost	$ 65,470,282	$ 69,933,553
Gross Unrealized Holding Gains	2,085,073	752,621
Gross Unrealized Holding Losses		(91,432)
Estimated Fair Value	67,555,355	70,594,742
Money Market Funds [Member]
Amortized Cost	3,546,052	7,903,433
Gross Unrealized Holding Gains
Gross Unrealized Holding Losses
Estimated Fair Value	3,546,052	7,903,433
Corporate Bond Securities [Member]
Amortized Cost	61,924,230	62,030,120
Gross Unrealized Holding Gains	2,085,073	752,621
Gross Unrealized Holding Losses		(91,432)
Estimated Fair Value	$ 64,009,303	$ 62,691,309

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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