Note 6 - Stock-based Compensation - Assumptions (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Risk-free interest rate		0.33%		0.33%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (Year)	5 years	5 years	5 years	5 years
Minimum [Member]
Risk-free interest rate	0.77%		0.46%
Expected volatility	47.10%	65.80%	47.10%	65.80%
Maximum [Member]
Risk-free interest rate	0.87%		0.92%
Expected volatility	47.70%	66.00%	92.60%	66.00%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
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