Note 3 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				9 Months Ended
	Aug. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2016
Warrants and Rights Outstanding		$ 3,902				$ 3,902			$ 178
Class of Warrant or Right, Outstanding		8,588,000				8,588,000		334,109	544,000
Class of Warrant or Right, Exercised During Period		102,602	158,400			394,000
Fair Value Adjustment of Warrants		$ (1,480)			$ (267)	$ (936)	$ (971)
Reclassification of Warrant Liability to Equity				$ 56
Class of Warrant or Right, Issued During Period						8,438,000
Warrants Reclassified Upon Adoption of ASU 2017-11 [Member]
Warrants and Rights Outstanding, Change in Fair Value		(228)				$ (84)
Fair Value Adjustment of Warrants		(75)				469
Reclassification of Warrant Liability to Equity		153				553
The August 2019 Warrants [Member]
Warrants and Rights Outstanding	$ 5,300
Fair Value Adjustment of Warrants		$ (1,400)				$ (1,400)
Class of Warrant or Right, Issued During Period	7,066,508
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	7,066,508
Accounting Standards Update 2017-11 [Member]
Warrants and Rights, Reclassified to Equity								210,586
Warrants and Rights Outstanding				$ (56)				$ (56)
Class of Warrant or Right, Number of Securities Called by Warrants or Rights										3,613,284