Note 7 - Share-based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares
Exercised, shares under options (in shares)	0
Employee and Nonemployee Stock Option [Member]
Outstanding, shares under options (in shares)	98,671
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 33.53
Granted, shares under options (in shares)	0
Exercised, shares under options (in shares)	0
Outstanding, shares under options (in shares)	98,671
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 33.53
Outstanding, weighted average remaining contractual life (Year)	5 years 6 months 25 days
Outstanding, aggregate intrinsic value | $	$ 3,221
Exercisable, shares under options (in shares)	87,955
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 30.63
Exercisable, weighted average remaining contractual life (Year)	5 years 1 month 13 days
Exercisable, aggregate intrinsic value | $	$ 3,126
Vested and expected to vest, shares under options (in shares)	98,671
Vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 33.53
Vested and expected to vest, weighted average remaining contractual life (Year)	5 years 6 months 25 days
Vested and expected to vest, aggregate intrinsic value | $	$ 3,221