Note 9 - Net Loss Per Share of Common Stock - Summary of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Net loss	$ (7,105)	$ (8,004)	$ (5,041)	$ (10,796)	$ (15,109)	$ (15,837)
Net loss per share - basic and diluted (in dollars per share)	$ (0.35)		$ (0.32)		$ (0.78)	$ (1.02)
Weighted-average common shares used to compute basic and diluted net loss per share (in shares)	20,414		15,902		19,247	15,457