Note 9 - Stock Based Awards - Activity Under Stock Option Plan (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares
Balances, number of shares (in shares) | shares	2,173,776
Balances, weighted average exercise price (in dollars per share) | $ / shares	$ 9.59
Options granted, number of shares (in shares) | shares	1,005,628
Options granted, weighted average exercise price (in dollars per share) | $ / shares	$ 5.26
Options cancelled, number of shares (in shares) | shares	(521,088)
Options cancelled, weighted average exercise price (in dollars per share) | $ / shares	$ 31.03
Options exercised, number of shares (in shares) | shares	(219,063)
Options exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 1.40
Balances, number of shares (in shares) | shares	2,439,253
Balances, weighted average exercise price (in dollars per share) | $ / shares	$ 3.96
Balances, weighted average remaining contractual life (Year)	7 years 1 month 6 days
Balances, aggregate intrinsic value | $	$ 1,611
Outstanding and expected to vest, number of shares (in shares) | shares	2,248,136
Outstanding and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 3.80
Outstanding and expected to vest, weighted average remaining contractual life (Year)	6 years 10 months 24 days
Outstanding and expected to vest, aggregate intrinsic value | $	$ 1,611
Exercisable, number of shares (in shares) | shares	1,477,273
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 2.68
Exercisable, weighted average remaining contractual life (Year)	5 years 9 months 18 days
Exercisable, aggregate intrinsic value | $	$ 1,611