Note 10 - Stock-based Compensation Plan - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Options outstanding, number of shares (in shares) | shares	438,200
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.25
Granted, number of shares (in shares) | shares	164,800
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 10.62
Exercised, number of shares (in shares) | shares	99,740
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 7.19
Options outstanding, number of shares (in shares) | shares	503,260
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 7.49