Note 5 - Stock-based Compensation (Details Textual) - USD ($)	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	5 years
Share-based Payment Arrangement, Expense	$ 45,572	$ 48,360
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		5.90%
Share-based Payment Arrangement, Exercise of Option, Tax Benefit	$ 9,971	$ 10,581
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term (Year)	5 years 255 days	6 years 219 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares)	28,000	24,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 230,540
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	191,140
Share-based Compensation Arrangement by Share Based Payment Award Options Grants in Period Fair Value	47,140
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 1,568
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	7.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	7.40%

Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Fair Value

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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