Note 5 - Fair Value of Financial Instruments - Reconciliation of Available-for-sale Securities (Details) - USD ($)	Dec. 31, 2021	Mar. 31, 2021
Amortized Cost	$ 56,738,624	$ 63,451,301
Gross Unrealized Holding Gains	772,080	1,570,195
Gross Unrealized Holding Losses	(216,834)	(160,674)
Estimated Fair Value	57,293,870	64,860,822
Amortized Cost	56,738,624	63,451,301
Money Market Funds [Member]
Amortized Cost	7,631,824	10,143,196
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	7,631,824	10,143,196
Amortized Cost	7,631,824	10,143,196
Corporate Bond Securities [Member]
Amortized Cost	49,106,800	53,308,105
Gross Unrealized Holding Gains	772,080	1,570,195
Gross Unrealized Holding Losses	(216,834)	(160,674)
Estimated Fair Value	49,662,046	54,717,626
Amortized Cost	$ 49,106,800	$ 53,308,105