Note 11 - Warrant Liabilities - Fair Value Assumptions Used to Determine the Value of Warrants Outstanding (Details) - Warrant [Member]	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Expected life in years (Year)	8 years 69 days
Volatility	111.00%
Risk-free interest rate	2.40%
Dividend rate	0.00%	0.00%
Minimum [Member]
Expected life in years (Year)		153 days
Volatility		76.00%
Risk-free interest rate		0.60%
Maximum [Member]
Expected life in years (Year)		9 years 69 days
Volatility		122.00%
Risk-free interest rate		2.50%

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

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Risk-free interest rate assumption used in valuing an instrument.

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