Note 5 - Marketable Securities - Reconciliation of Marketable Securities (Details) - USD ($)	Sep. 30, 2017	Mar. 31, 2017
Adjusted Cost	$ 76,498,214	$ 76,462,904
Gross Unrealized Gains	197,573	187,001
Gross Unrealized Losses	(151,289)	(247,149)
Fair Market Value	76,544,498	76,402,756
Corporate Bond Securities [Member]
Adjusted Cost	76,498,214	75,158,087
Gross Unrealized Gains	197,573	187,001
Gross Unrealized Losses	(151,289)	(246,935)
Fair Market Value	76,544,498	75,098,153
Municipal Bonds [Member]
Adjusted Cost		1,304,817
Gross Unrealized Gains
Gross Unrealized Losses		(214)
Fair Market Value		$ 1,304,603

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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