Note 13 - Net Loss Per Share Available to Common Stockholders - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net loss	$ (41,244)	$ (31,491)	$ (16,480)
Weighted-average shares used to compute net loss per share available to common stockholders, basic and diluted (in shares)	5,783	5,638	5,474
Net loss per share available to common stockholders:
Net loss per share available to common stockholders, basic and diluted (in dollars per share)	$ (7.13)	$ (5.59)	$ (3.01)