Note 6 - Shareholders' Equity - Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2023	Dec. 31, 2022
Stock options outstanding (in shares)	1,382,246	1,539,278
Stock options and restricted stock units available for future grant (in shares)	920,743
Common stock reserved for future issuance (in shares)	2,573,446
Restricted Stock Units and Performance Stock Units [Member]
Restricted stock units and performance stock units outstanding (in shares)	270,457

Aggregate number of common shares reserved for future issuance.

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-Topic 210
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-Section S99
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-Publisher FASB
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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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-Topic 718
-SubTopic 10
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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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

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