Note 12 - Summary of Stock Options - Valuation Assumption for Employee Stock Purchase Plan (Details) |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2020 |
Jun. 30, 2019 |
Jun. 30, 2020 |
Jun. 30, 2019 |
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| Expected term (Year) | 5 years | 5 years | 5 years | |
| Average volatility | 75.00% | 73.00% | 73.00% | |
| Risk-free interest rate | 2.03% | 0.45% | 2.49% | |
| Dividend yield | 0.00% | 0.00% | 0.00% | |
| 2017 Employee Stock Purchase Plan [Member] | ||||
| Expected term (Year) | 91 days | 91 days | 91 days | 91 days |
| Average volatility | 110.00% | 87.00% | 117.00% | 81.00% |
| Risk-free interest rate | 0.09% | 2.43% | 0.84% | 2.44% |
| Dividend yield | 0.00% | 0.00% | 0.00% | 0.00% |
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- Definition 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. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Rate of weighted-average expected volatility for award under share-based payment arrangement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Details
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