Note 3 - Fair Value of Financial Instruments - Assets Measured on Recurring Basis (Details) - USD ($)	Mar. 31, 2020	Mar. 31, 2019
Securities available for sale	$ 70,594,742	$ 74,117,263
Money Market Funds [Member]
Securities available for sale	7,903,433	6,703,809
Corporate Bond Securities [Member]
Securities available for sale	62,691,309	67,413,454
Fair Value, Recurring [Member]
Securities available for sale	70,594,742	74,117,263
Fair Value, Recurring [Member] | Money Market Funds [Member]
Securities available for sale	7,903,433	6,703,809
Fair Value, Recurring [Member] | Corporate Bond Securities [Member]
Securities available for sale	62,691,309	67,413,454
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	7,903,433	6,703,809
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Securities available for sale	7,903,433	6,703,809
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Securities available for sale
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	62,691,309	67,413,454
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Securities available for sale
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Securities available for sale	$ 62,691,309	$ 67,413,454