Note 13 - Stock Based Compensation - Stock Option Activity (Details) - USD ($)	6 Months Ended
Jun. 30, 2020
Outstanding, shares (in shares)	4,308,383
Outstanding, weighted average exercise price per share (in dollars per share)	$ 3.44
Outstanding, aggreate instrinsic value	$ 651,000
Granted, shares (in shares)	2,915,000
Granted, weighted average exercise price per share (in dollars per share)	$ 1.66
Granted, aggreate instrinsic value	$ 374,000
Forfeited, shares (in shares)
Forfeited, weighted average exercise price per share (in dollars per share)
Expired, shares (in shares)
Expired, weighted average exercise price per share (in dollars per share)
Outstanding, shares (in shares)	7,223,383
Outstanding, weighted average exercise price per share (in dollars per share)	$ 2.72
Outstanding, weighted average contractual life remaining in years (Year)	9 years 18 days
Outstanding, aggreate instrinsic value	$ 15,214,250
Exercisable, shares (in shares)	4,163,814
Exercisable, Weighted average exercise price per share (in dollars per share)	$ 3.45
Exercisable, weighted average contractual life remaining in years (Year)	8 years 200 days
Exercisable, aggreate instrinsic value	$ 8,821,400
Vested and expected to vest, shares (in shares)	7,223,383
Vested and expected to vest, Weighted average exercise price per share (in dollars per share)	$ 2.72
Vested and expected to vest, weighted average contractual life remaining in years (Year)	9 years 18 days
Vested and expected to vest, aggreate instrinsic value	$ 15,214,250

Intrinsic value of options granted during the period.

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

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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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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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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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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 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 grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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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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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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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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