Note 6 - Income Taxes - Reconciliation of Income Tax Provisions (Details) - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Tax expense at U.S. statutory rate	$ 3,719,066	$ 6,282,771
State income taxes, net of Federal benefit	95,430	103,240
Domestic manufacturing deduction		(495,361)
Foreign-derived intangible income deduction	(555,256)
Municipal interest		(1,378)
Tax Reform Act effect on deferred tax assets		206,693
Other	(57,337)	187
Income tax provision	$ 3,201,903	$ 6,096,152