Note 11 - Equity Incentive Plan - Assumptions Used to Estimate Fair Value of Stock Options and Stock Appreciation Rights (Details)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Expected life (years) (Year)	4 years	4 years
Expected dividend yield	0.00%	0.00%
Minimum [Member]
Risk free interest rate	0.30%	0.40%
Expected volatility	54.80%	46.50%
Maximum [Member]
Risk free interest rate	0.60%	1.60%
Expected volatility	55.40%	49.40%

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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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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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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