Note 13 - Warrants (Details Textual) - USD ($)	12 Months Ended		28 Months Ended	58 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Dec. 31, 2017	Jun. 26, 2017	Jun. 09, 2017	Jun. 13, 2016
Number Of Warrants Issued	9,231,628	1,147,595
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					506,627	790,410
Proceeds from Warrant Exercises	$ 21,140,304	$ 2,500	$ 800,000	$ 2,100,000
June 2016 Common Stock Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							630,252
Hercules Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	7,617,147			7,617,147
Proceeds from Warrant Exercises	$ 22,000,000
Series B Warrant [Member] | June 2016 Common Stock Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, Exercise of Warrants		17,857