Note 12 - Share-based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Options outstanding (in shares) | shares	192,000
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 19.46
Issued (in shares) | shares	78,000
Issued, weighted average exercise price (in dollars per share) | $ / shares	$ 29.43
Exercised (in shares) | shares	(8,800)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 15.39
Forfeited or expired (in shares) | shares	(3,800)
Forfeited or expired, weighted average exercise price (in dollars per share) | $ / shares	$ 19.96
Options outstanding (in shares) | shares	257,400
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 22.61
Options outstanding, weighted average remaining term (Year)	5 years 7 months 6 days
Options outstanding, intrinsic value | $	$ 1,510,216
Expected to vest (in shares) | shares	150,500
Expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 24.91
Expected to vest, weighted average remaining term (Year)	6 years 10 months 24 days
Expected to vest, intrinsic value | $	$ 580,937
Exercisable (in shares) | shares	106,900
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 19.38
Exercisable, weighted average remaining term (Year)	3 years 9 months 18 days
Exercisable, intrinsic value | $	$ 929,279