Note 12 - Stock-based Compensation Plan - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Options outstanding, number of shares (in shares)	264,400	76,400
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.54	$ 5.98
Granted, number of shares (in shares)	249,460	189,800
Granted, weighted average exercise price (in dollars per share)	$ 6.25	$ 8.14
Exercised, number of shares (in shares)
Canceled, number of shares (in shares)	7,050	1,800
Canceled, weighted average exercise price (in dollars per share)	$ 8.45	$ 4.37
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