Note 13 - Stock-based Compensation Plan - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options outstanding, number of shares (in shares)	506,810	264,400
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.89	$ 7.54
Granted, number of shares (in shares)	113,980	249,460
Granted, weighted average exercise price (in dollars per share)	$ 3.49	$ 6.25
Exercised, number of shares (in shares)
Canceled, number of shares (in shares)	182,590	7,050
Canceled, weighted average exercise price (in dollars per share)	$ 6.31	$ 8.45
Options outstanding, number of shares (in shares)	438,200	506,810
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.25	$ 6.89