Note 2 - Summary of Significant Accounting Policies - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net loss	$ (9,658)	$ (6,545)	$ (7,403)
Less: Preferred deemed dividend	(800)
Warrant, Down Round Feature, (Increase) Decrease in Equity, Amount	29
Net loss attributable to common stockholders	(10,487)	(6,545)	(7,403)
Less gain on changes in fair value of warrant liability		(1,311)
Net loss attributable to common stockholders, diluted	$ (10,487)	$ (7,856)	$ (7,403)
Weighted average shares outstanding, basic (in shares)	21,641	16,921	15,324
Net loss per share, basic (in dollars per share)	$ (0.48)	$ (0.39)	$ (0.48)
Effect of dilutive warrants (in shares)		137
Weighted average shares outstanding, diluted (in shares)	21,641	17,058	15,324
Net loss per share, diluted (in dollars per share)	$ (0.48)	$ (0.46)	$ (0.48)