Note 2 - Summary of Significant Accounting Policies - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net loss	$ (17,325)	$ (12,589)	$ (7,266)
Basic and diluted weighted average number of shares outstanding (in shares)	28,517,339	22,397,865	20,897,812
Basic loss per common share (in dollars per share)	$ (0.61)	$ (0.56)	$ (0.35)
Diluted loss per common share (in dollars per share)	$ (0.61)	$ (0.56)	$ (0.35)