Note 1 - Summary of Significant Accounting Policies - Valuation Assumptions (Details)	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Expected dividend yield	0.00%	0.00%
Expected life (yeas) (Year)	10 years	10 years
Minimum [Member]
Expected stock price volatility	82.60%	78.60%
Risk-free interest rate	0.62%	2.00%
Maximum [Member]
Expected stock price volatility	86.80%	79.80%
Risk-free interest rate	1.78%	2.76%
Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input	0	0
Measurement Input, Price Volatility [Member] \| Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.826	0.786
Measurement Input, Price Volatility [Member] \| Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.868	0.798
Measurement Input, Risk Free Interest Rate [Member] \| Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0033	0.0193
Measurement Input, Risk Free Interest Rate [Member] \| Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	0.0079	0.0258
Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input		5
Measurement Input, Expected Term [Member] \| Minimum [Member]
Warrants and Rights Outstanding, Measurement Input	2
Measurement Input, Expected Term [Member] \| Maximum [Member]
Warrants and Rights Outstanding, Measurement Input	5.5

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.

+ References

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- Definition

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

+ References

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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.

+ References

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=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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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- Definition

Value of input used to measure outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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