Note 5 - Fair Value of Financial Instruments (Tables)

6 Months Ended

Sep. 30, 2018

Notes Tables

Investments Classified by Contractual Maturity Date [Table Text Block]

Total		<1 Year		1–3 Years		3–5 Years
$	76,576,286	$	29,716,134	$	22,784,235	$	24,075,917

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

	As of September 30, 2018						As of March 31, 2018
	Level 1		Level 2		Total		Level 1		Level 2		Total
Money market funds	$	5,774,385	$	-	$	5,774,385	$	3,951,032	$	-	$	3,951,032
Corporate bonds		-		70,801,901		70,801,901		54,517,969		19,085,998		73,603,967
Total	$	5,774,385	$	70,801,901	$	76,576,286	$	58,469,001	$	19,085,998	$	77,554,999

Schedule of Available-for-sale Securities Reconciliation [Table Text Block]

	As of September 30, 2018									As of March 31, 2018
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	5,774,385	$	-	$	-		$	5,774,385	$	3,951,032	$	-	$	-		$	3,951,032
Corporate bonds		72,122,677		-		(1,320,776	)		70,801,901		74,853,327		-		(1,249,360	)		73,603,967
Total	$	77,897,062	$	-	$	(1,320,776	)	$	76,576,286	$	78,804,359	$	-	$	(1,249,360	)	$	77,554,999

Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block]

	Less Than 12 Months					12 Months or Greater					Total
	Estimated Fair Value		Gross Unrealized Holding Losses			Estimated Fair Value		Gross Unrealized Holding Losses			Estimated Fair Value		Gross Unrealized Holding Losses
As of September 30, 2018
Corporate bonds	$	47,928,537	$	(580,584	)	$	22,873,364	$	(740,192	)	$	70,801,901	$	(1,320,776	)
Total	$	47,928,537	$	(580,584	)	$	22,873,364	$	(740,192	)	$	70,801,901	$	(1,320,776	)
As of March 31, 2018
Corporate bonds	$	61,731,248	$	(1,003,849	)	$	9,072,719	$	(245,511	)	$	70,803,967	$	(1,249,360	)
Total	$	61,731,248	$	(1,003,849	)	$	9,072,719	$	(245,511	)	$	70,803,967	$	(1,249,360	)