Note 9 - Stockholders' Equity - Schedule of Warrants Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding Warrants to Purchase Shares (in shares)	3,875,699	0	0
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 0	$ 0
Class of Warrant or Right, Exercise Price of Warrants or Rights
The 2014 Public Offering [Member]
Outstanding Warrants to Purchase Shares (in shares)	6,483
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 540
Class of Warrant or Right, Exercise Price of Warrants or Rights	January 29, 2019
The 2018 Warrants [Member]
Outstanding Warrants to Purchase Shares (in shares)	3,869,216
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 4.048
Class of Warrant or Right, Exercise Price of Warrants or Rights	May 30, 2022