Note 4 - Computation of Net Loss Per Common Share - Reconciliation of Numerators and Denominators of EPS Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net loss	$ (3,712)	$ (3,417)	$ (825)	$ (3,539)	$ (7,129)	$ (4,364)
Fair Value Adjustment of Warrants			(1,145)			(4,092)
Plus: change in fair value due to exercise of warrants						83
Net income (loss) - diluted	$ (3,712)		$ (1,970)		$ (7,129)	$ (8,373)
Weighted-average shares of common stock outstanding (in shares)	23,057		21,678		22,943	21,538
Weighted-average shares subject to repurchase (in shares)	(1,197)		(1,022)		(1,168)	(952)
Shares used in per-share calculation - basic (in shares)	21,860		20,656		21,775	20,586
Common stock warrants (in shares)			67			150
Shares used in per-share calculation - diluted (in shares)	21,860		20,723		21,775	20,736
Net loss per share ? basic (in dollars per share)	$ (0.17)		$ (0.04)		$ (0.33)	$ (0.21)
Net loss per share ? diluted (in dollars per share)	$ (0.17)		$ (0.10)		$ (0.33)	$ (0.40)