Note 9 - Stock-based Compensation - Assumptions Used in Calculating Fair Value of Options (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Expected dividend yield	0.00%	0.00%
Expected stock price volatility	72.00%	72.00%
Minimum [Member]
Common stock fair value (in dollars per share)	$ 2.95	$ 3.50
Risk-free interest rate	1.55%	2.30%
Expected option life (Year)	5 years	1 year 91 days
Expected stock price volatility
Maximum [Member]
Common stock fair value (in dollars per share)	$ 5	$ 8.10
Risk-free interest rate	2.25%	2.94%
Expected option life (Year)	5 years 182 days	5 years 273 days
Expected stock price volatility

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

Price of a single share of a number of saleable stocks of a company.

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No definition available.

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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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