Note 12 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Options outstanding (in shares)	3,173,103
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.51
Options outstanding, weighted average remaining contractual term (Year)	9 years	9 years
Options outstanding, aggregate intrinsic value	$ 0	$ 0
Options granted (in shares)	941,000
Options granted, weighted average exercise price (in dollars per share)	$ 1.26
Options exercised (in shares)	0
Options exercised, weighted average exercise price (in dollars per share)
Options canceled (in shares)	(4,094)
Options canceled, weighted average exercise price (in dollars per share)	$ 7.69
Options outstanding (in shares)	4,110,009	3,173,103
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.08	$ 7.51
Vested and exercisable and expected to vest (in shares)	3,818,956
Vested and exercisable and expected to vest, end of period, weighted average exercise price (in dollars per share)	$ 6.34
Vested and exercisable and expected to vest, end of period, weighted average remaining contractual term (Year)	9 years
Vested and exercisable and expected to vest, end of period, aggregate intrinsic value	$ 0
Vested and exercisable (in shares)	995,692
Vested and exercisable, end of period, weighted average exercise price (in dollars per share)	$ 15.65
Vested and exercisable, end of period, weighted average remaining contractual term (Year)	8 years 4 months 24 days
Vested and exercisable, end of period, aggregate intrinsic value	$ 0