Note 10 - Stockholders' Equity - Option Activity for Stock Option Plans (Details) - $ / shares	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Outstanding, options (in shares)	889,636
Outstanding, weighted average exercise price, options (in dollars per share)	$ 8.57
Cancelled / Forfeited, options (in shares)		503,050
Outstanding, options (in shares)	386,461	889,636
Outstanding, weighted average exercise price, options (in dollars per share)	$ 11.88	$ 8.57
Outstanding, weighted average remaining contractual life, options (Year)	7 years 4 months 24 days
Vested and expected to vest, options (in shares)	335,786
Vested and expected to vest, weighted average exercise price, options (in dollars per share)	$ 9.15
Vested and expected to vest, weighted average remaining contractual life, options (Year)	7 years 3 months 18 days
Exercisable, options (in shares)	244,211
Exercisable, weighted average exercise price, options (in dollars per share)	$ 10.31
Exercisable, weighted average remaining contractual life, options (Year)	7 years 1 month 6 days

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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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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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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Number of fully vested and expected to vest options outstanding that can 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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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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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 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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