Note 7 - Income Taxes - Reconciliation of Income Tax Provisions (Details) - USD ($)	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Tax expense at U.S. statutory rate	$ 6,645,733	$ 6,272,341	$ 7,503,886
State income taxes, net of Federal benefit	83,116	118,057	216,518
Domestic manufacturing deduction	(536,063)	(476,932)	(600,207)
Municipal interest	(4,207)	(4,171)	(11,489)
Other	(41,437)	(24,513)	(37,388)
Income tax provision	$ 6,147,142	$ 5,884,782	$ 7,071,320

Income Tax Reconciliation, Municipal Interest

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments.

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