Note 2 - Liquidity (Details Textual) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
May 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001	$ 0.001
Warrants Issued in Connection with May 2019 Public Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,317,060
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 5
May 2019 Public Offering [Member]
Stock Issued During Period, Shares, New Issues	1,317,060
Shares Issued, Price Per Share	$ 4.895
Proceeds from Issuance or Sale of Equity, Total	$ 5.6

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

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