Note 11 - Stock-based Compensation - Fair Value of Option Assumptions (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Minimum [Member]
Risk-free interest rate		1.55%
Expected volatility		87.50%
Maximum [Member]
Risk-free interest rate		1.87%
Expected volatility		89.10%
Expected life (Year)		10 years
Expected forfeiture rate		5.00%
Expected dividend yield		0.00%
Employee Stock Option [Member] \| Minimum [Member]
Risk-free interest rate	2.21%
Expected volatility	90.40%
Employee Stock Option [Member] \| Maximum [Member]
Risk-free interest rate	2.32%
Expected volatility	100.80%
Expected life (Year)	10 years
Expected forfeiture rate	0.00%
Expected dividend yield	0.00%

The estimated forfeiture rate of share-based payment awards.

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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.

+ References

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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

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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=27013229&loc=d3e301413-122809

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