Note 9 - Share-based Compensation - Stock Option Activity Under Equity Incentive Plans and Director Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Exercised, number of options (in shares)	(116,753)	(630,373)	(227,902)
Common Stock Options [Member]
Beginning balance, outstanding, number of options (in shares)	600,571
Beginning balance, outstanding, weighted average exercise price (in dollars per share)	$ 25.31
Granted, number of options (in shares)	101,091	70,471	100,615
Granted, weighted average exercise price (in dollars per share)	$ 44.96
Exercised, number of options (in shares)	(116,753)
Exercised, weighted average exercise price (in dollars per share)	$ 13.14
Intrinsic value of stock options exercised (in thousands)	$ 3,535
Expired, number of options (in shares)	(22,837)
Expired, weighted average exercise price (in dollars per share)	$ 9.74
Forfeited, number of options (in shares)	(84,432)
Forfeited, weighted average exercise price (in dollars per share)	$ 38.38
Ending balance, outstanding, number of options (in shares)	477,640	600,571
Ending balance, outstanding, weighted average exercise price (in dollars per share)	$ 30.88	$ 25.31
Outstanding, weighted average remaining contractual term (Year)	5 years 11 months 19 days
Outstanding, aggregate intrinsic value	$ 6,337
Exercisable, number of options (in shares)	249,488
Weighted average exercise price (in dollars per share)	$ 23.99
Exercisable, weighted average remaining contractual term (Year)	4 years 9 months 25 days
Exercisable, aggregate intrinsic value	$ 4,805