Note 11 - Financial Instruments - Estimated Fair Value of Outstanding Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Warrants outstanding (in shares)	333,500	1,976,389
Warrant shares outstanding (in shares)	125,896	424,923
Term (Year)	5 years	5 years
Warrant exercise price (in dollars per share)	$ 6.60	$ 11.60
Warrant fair value liability	$ 281	$ 1,915

Exercise price per share or per unit of warrants or rights outstanding.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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Number of warrants or rights outstanding.

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Fair value as of the balance sheet date of all price risk derivative liabilities not designated as hedging instruments.

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Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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