Note 5 - Fair Value of Financial Instruments - Assets Measured on Recurring Basis (Details) - USD ($)	Jun. 30, 2019	Mar. 31, 2019
Total	$ 61,611,878	$ 74,117,263
Money Market Funds [Member]
Total	12,774,255	6,703,809
Corporate Bond Securities [Member]
Total	61,611,878	67,413,454
Fair Value, Recurring [Member]
Total	74,386,133	74,117,263
Fair Value, Recurring [Member] | Money Market Funds [Member]
Total	12,774,255	6,703,809
Fair Value, Recurring [Member] | Corporate Bond Securities [Member]
Total	61,611,878	67,413,454
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Total	12,774,255	6,703,809
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Total	12,774,255	6,703,809
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	61,611,878	67,413,454
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	$ 61,611,878	$ 67,413,454