Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Dec. 31, 2018	Mar. 31, 2018
Amortized Cost	$ 76,458,563	$ 78,804,359
Gross Unrealized Holding Gains	19,403
Gross Unrealized Holding Losses	(1,209,750)	(1,249,360)
Estimated Fair Value	75,268,216	77,554,999
Money Market Funds [Member]
Amortized Cost	5,915,078	3,951,032
Gross Unrealized Holding Gains
Gross Unrealized Holding Losses
Estimated Fair Value	5,915,078	3,951,032
Corporate Bond Securities [Member]
Amortized Cost	70,543,485	74,853,327
Gross Unrealized Holding Gains	19,403
Gross Unrealized Holding Losses	(1,209,750)	(1,249,360)
Estimated Fair Value	$ 69,353,138	$ 73,603,967

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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Amount, before tax, of unrealized loss 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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