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Note 7 - Stockholders' Equity and Common Stock Warrants (Details Textual) - USD ($)	1 Months Ended				12 Months Ended
	Dec. 31, 2019	Nov. 30, 2019	May 31, 2019	Jan. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Proceeds from Issuance or Sale of Equity, Total					$ 16,000,000
Proceeds from Warrant Exercises					3,888,425
Conversion of Stock, Shares Issued				1,400,462
Stock Issued During Period, Shares, Conversion of Convertible Securities				553,752
Common Stock Dividends, Shares				68,815
Stock Issued During Period, Shares, Make-whole Adjustment				777,895
Dividends, Make-whole Adjustment				$ 8,200,000		$ 8,167,895
Class of Warrant or Rights, Expired					1,767	28,123
Warrants Issued in Connection with the December 2019 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	6,266,787				6,266,787
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 0.4335				$ 0.4335
Warrants Issued in Connection with the December 2019 Offering [Member] \| Maximum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 0.6981				$ 0.6981
Placement Agent Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	313,339	571,429	65,853		313,339
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 0.6981	$ 0.4375	$ 6.11875		$ 0.6981
Warrants and Rights Outstanding, Term	5 years	5 years	5 years		5 years
Warrants Issued in Connection with the November 2019 Offering [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 0.35
Class of Warrant or Right, Issued During Period		6,324,143
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right		1
Class of Warrant or Right, Exercised During Period					11,091,716
Proceeds from Warrant Exercises					$ 3,900,000
Warrants Issued in Connection with the November 2019 Offering [Member] \| Maximum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 0.4375				$ 0.4375
Warrants with 18 Months Term Issued in Connection with the November 2019 Offering [Member]
Warrants and Rights Outstanding, Term		1 year 180 days
Class of Warrant or Right, Issued During Period		11,428,572
Warrants with 5 Years Term Issued in Connection with the November 2019 Offering [Member]
Warrants and Rights Outstanding, Term		5 years
Class of Warrant or Right, Issued During Period		11,428,572
Warrants Issued in Connection with the January 2018 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				1,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 12
Warrants Issued in Connection with the January 2018 Offering [Member] \| Maximum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 15				15
Option Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				150,000
Additional Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 12
Class of Warrant or Right, Granted				131,375
Underwriter Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 15
Class of Warrant or Right, Term				5 years
Underwriter Warrants [Member] \| Maximum [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				50,000
December 2019 Public Offering [Member]
Stock Issued During Period, Shares, New Issues	6,266,787
Shares Issued, Price Per Share	$ 0.5585				$ 0.5585
Proceeds from Issuance or Sale of Equity, Total	$ 3,000,000
November 2019 Public Offering [Member]
Stock Issued During Period, Shares, New Issues		5,104,429
Shares Issued, Price Per Share		$ 0.35
Proceeds from Issuance or Sale of Equity, Total		$ 3,300,000
Stock and Warrants Issued During Period, Number of Securities Called by Stock and Warrants		22,857,144
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			$ 5,600,000
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
January 2018 Offering [Member]
Stock Issued During Period, Shares, New Issues				1,000,000
Proceeds from Issuance or Sale of Equity, Total				$ 10,800,000
Stock Issued During Period, Shares, Issued for Services				150,000