Stock options roll foward (Details) - USD ($)	12 Months Ended
May 31, 2022	May 31, 2021	May 31, 2020
Share-Based Payment Arrangement, Noncash Expense [Abstract]
Stock options outstanding	283,000	267,750	252,250
Weighted average exercise price of options outstanding	$ 11.43	$ 11.60	$ 11.52
Intrinsic value of options outstanding	$ 28,248	$ 271,426	$ 209,835
Options granted	66,750	47,250
Weighted average exercise price of options granted	$ 10.69	$ 11.26
Stock options exercised		13,000
Weighted average exercise price of options exercised		$ 6.34
Stock options expired	51,500		18,750

No definition available.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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Gross number of share options (or share units) granted during the period.

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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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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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