Note 12 - Summary of Stock Options - Valuation Assumptions for Stock Options (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Expected term (Year)	5 years	5 years	5 years
Average volatility	87.00%	81.00%	73.00%
Risk-free interest rate	0.27%	0.34%	2.49%
Dividend yield

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

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- Definition

Rate of weighted-average expected volatility for award under share-based payment arrangement.

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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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