Note 5 - Fair Value of Financial Instruments - Assets Measured on Recurring Basis (Details) - USD ($)	Jun. 30, 2020	Mar. 31, 2020
Total	$ 70,315,124	$ 70,594,742
Money Market Funds [Member]
Total	6,086,051	7,903,433
Corporate Bond Securities [Member]
Total	64,229,073	62,691,309
Fair Value, Recurring [Member]
Total	70,315,124	70,594,742
Fair Value, Recurring [Member] | Money Market Funds [Member]
Total	6,086,051	7,903,433
Fair Value, Recurring [Member] | Corporate Bond Securities [Member]
Total	64,229,073	62,691,309
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total	6,086,051	7,903,433
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Total	6,086,051	7,903,433
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Total
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Total	64,229,073	62,691,309
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Total
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Total	$ 64,229,073	$ 62,691,309