Note 5 - Fair Value of Financial Instruments - Assets Measured on Recurring Basis (Details) - USD ($)	Dec. 31, 2019	Mar. 31, 2019
Securities available for sale	$ 72,853,414	$ 74,117,263
Money Market Funds [Member]
Securities available for sale	9,877,760	6,703,809
Corporate Bond Securities [Member]
Securities available for sale	62,975,654	67,413,454
Fair Value, Recurring [Member]
Securities available for sale	72,853,414	74,117,263
Fair Value, Recurring [Member] | Money Market Funds [Member]
Securities available for sale	9,877,760	6,703,809
Fair Value, Recurring [Member] | Corporate Bond Securities [Member]
Securities available for sale	62,975,654	67,413,454
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	9,877,760	6,703,809
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Securities available for sale	9,877,760	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	62,975,654	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	$ 62,975,654	$ 67,413,454