Note 4 - Stockholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Outstanding, number of units, balance (in shares)	3,498,297
Outstanding, weighted average exercise price, beginning balance (in dollars per share)	$ 10.07
Outstanding, weighted average remaining contractual term (Year)	7 years 7 months 20 days	7 years 3 months 7 days
Outstanding, aggregate intrinsic value	$ 946	$ 7,456
Granted, number of units (in shares)	760,000
Granted, weighted average exercise price (in dollars per share)	$ 5.07
Exercised, cancelled, or forfeited, number of units (in shares)	(69,291)
Exercised, cancelled, or forfeited, weighted average exercise price (in dollars per share)	$ 14.44
Outstanding, number of units, balance (in shares)	4,189,006	3,498,297
Outstanding, weighted average exercise price, balance (in dollars per share)	$ 9.08	$ 10.07
Exercisable, number of units (in shares)	2,116,338
Exercisable, weighted average exercise price (in dollars per share)	$ 10.75
Exercisable, weighted average remaining contractual term (Year)	6 years 1 month 6 days
Exercisable, aggregate intrinsic value	$ 629