Note 6 - Stock-based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares
Outstanding at January 1, 2022 (in shares) | shares	1,306,824
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.87
Granted (in shares) | shares	0
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Exercised (in shares) | shares	(58,750)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 3.81
Forfeited or expired (in shares) | shares	(43,584)
Forfeited or expired, weighted average exercise price (in dollars per share) | $ / shares	$ 6.75
Outstanding at March 31, 2022 (in shares) | shares	1,204,490
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 7.02
Outstanding, weighted average remaining contractual term (Year)	4 years 3 months 21 days
Outstanding, aggregate intrinsic value | $	$ 154
Vested and expected to vest at March 31, 2022 (in shares) | shares	1,086,934
Options vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 7.03
Options vested and expected to vest, weighted average remaining contractual term (Year)	4 years 1 month 28 days
Options vested and expected to vest, aggregate intrinsic value | $	$ 152
Exercisable at March 31, 2022 (in shares) | shares	644,453
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 7.13
Exercisable, weighted average remaining contractual term (Year)	2 years 11 months 15 days
Exercisable, aggregate intrinsic value | $	$ 145