Note 9 - Stockholders' Equity - Stock Options Outstanding (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Outstanding, number of options (in shares)	3,758,670
Outstanding, weighted average exercise price per share (in dollars per share)	$ 4.26
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	4 years 3 months 18 days	4 years 8 months 12 days
Outstanding, Aggregate Intrinsic Value	$ 1,662	$ 270
Granted, number of options (in shares)	957,000
Granted, weighted average exercise price per share (in dollars per share)	$ 2.65
Exercised, number of options (in shares)	(100,278)	(22,373)
Exercised, weighted average exercise price per share (in dollars per share)	$ 2.27	$ 3.35
Exercised, Aggregate Intrinsic Value	$ 75
Forfeited or expired, number of options (in shares)	(234,044)
Forfeited or expired, weighted average exercise price per share (in dollars per share)	$ 6.14
Outstanding, number of options (in shares)	4,381,348	3,758,670
Outstanding, weighted average exercise price per share (in dollars per share)	$ 3.85	$ 4.26
Vested and expected to vest, number of options (in shares)	4,269,151
Vested and expected to vest, weighted average exercise price per share (in dollars per share)	$ 3.88
Vested and expected to vest,Weighted Average Remaining Contractual Term (Year)	4 years 2 months 12 days
Vested and expected to vest, Aggregate Intrinsic Value	$ 1,586
Exercisable, number of options (in shares)	2,889,095
Exercisable, weighted average exercise price per share (in dollars per share)	$ 4.42
Exercisable,Weighted Average Remaining Contractual Term (Year)	3 years 7 months 6 days
Exercisable, Aggregate Intrinsic Value	$ 701

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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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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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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

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