Note 6 - Share-based Compensation - Stock Option Activity Under Equity Incentive Plans and Director Plan (Details) - Common Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Beginning balance, outstanding, number of options (in shares)	477,640
Beginning balance, outstanding, weighted average exercise price (in dollars per share)	$ 30.88
Outstanding, weighted average remaining contractual term (Year)	5 years 8 months 1 day		5 years 11 months 19 days
Outstanding, aggregate intrinsic value	$ 5,709		$ 6,337
Granted, number of options (in shares)	54,759	51,002
Granted, weighted average exercise price (in dollars per share)	$ 42.25
Ending balance, outstanding, number of options (in shares)	532,399		477,640
Ending balance, outstanding, weighted average exercise price (in dollars per share)	$ 32.05		$ 30.88
Exercisable, number of options (in shares)	303,921
Weighted average exercise price (in dollars per share)	$ 23.06
Exercisable, weighted average remaining contractual term (Year)	3 years 9 months 14 days
Exercisable, aggregate intrinsic value	$ 5,553