Note 8 - Stock Based Awards - Activity Under Stock Option Plan (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares
Balances, number of shares (in shares) | shares	2,439,253
Balances, weighted average exercise price (in dollars per share) | $ / shares	$ 3.96
Options granted, number of shares (in shares) | shares	1,543,200
Options granted, weighted average exercise price (in dollars per share) | $ / shares	$ 2.14
Options cancelled, number of shares (in shares) | shares	(305,378)
Options cancelled, weighted average exercise price (in dollars per share) | $ / shares	$ 3.70
Options exercised, number of shares (in shares) | shares	0
Options exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Balances, number of shares (in shares) | shares	3,677,075
Balances, weighted average exercise price (in dollars per share) | $ / shares	$ 3.22
Balances, weighted average remaining contractual life (Year)	7 years 9 months 18 days
Balances, aggregate intrinsic value | $	$ 1,379
Outstanding and expected to vest, number of shares (in shares) | shares	3,176,415
Outstanding and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 3.23
Outstanding and expected to vest, weighted average remaining contractual life (Year)	7 years 6 months
Outstanding and expected to vest, aggregate intrinsic value | $	$ 1,377
Exercisable, number of shares (in shares) | shares	1,647,359
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 2.89
Exercisable, weighted average remaining contractual life (Year)	5 years 8 months 12 days
Exercisable, aggregate intrinsic value | $	$ 1,371