Note 8 - Warrants (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Class of Warrant or Right, Outstanding	3,963,505	3,963,505	4,080,005
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 4.33	$ 4.33	$ 4.35
Class of Warrant or Right, Exercised During Period	87,500	116,500
Class of Warrant or Right, Exercised During Period, Exercise Price	$ 4.75	$ 4.75
Proceeds from Warrant Exercises	$ 416,000	$ 553,000