Note 5 - Stockholders' Equity and Common Stock Warrants (Details Textual) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	May 31, 2019	Sep. 30, 2019
Class of Warrant or Rights, Expired		100
Class of Warrant or Right, Exercised		0
Placement Agent Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	65,853
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 6.11875
Warrants and Rights Outstanding, Term	5 years
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
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