Note 6 - Stock-based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) $ / shares shares
Outstanding at January 1, 2022 (in shares) | shares	1,306,824	1,306,824
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.87	$ 6.87
Granted (in shares) | shares		5,000
Granted (in dollars per share) | $ / shares		$ 4.68
Exercised (in shares) | shares		(58,750)
Exercised, weighted average exercise price (in dollars per share) | $ / shares		$ 3.81
Forfeited or expired (in shares) | shares		(44,834)
Forfeited or expired, weighted average exercise price (in dollars per share) | $ / shares		$ 6.76
Outstanding at March 31, 2022 (in shares) | shares		1,208,240
Outstanding, weighted average exercise price (in dollars per share) | $ / shares		$ 7.01
Outstanding, weighted average remaining contractual term (Year)		4 years 25 days
Outstanding, aggregate intrinsic value | $	$ 33
Vested and expected to vest at March 31, 2022 (in shares) | shares	1,103,948
Options vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 7.01
Options vested and expected to vest, weighted average remaining contractual term (Year)	3 years 11 months 4 days
Options vested and expected to vest, aggregate intrinsic value | $		$ 33
Exercisable at March 31, 2022 (in shares) | shares		717,956
Exercisable, weighted average exercise price (in dollars per share) | $ / shares		$ 7.06
Exercisable, weighted average remaining contractual term (Year)		2 years 11 months 4 days
Exercisable, aggregate intrinsic value | $		$ 33