Note 11 - Shareholders' Equity - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance, number of shares (in shares)	1,786,891	1,544,826
Balance, weighted average exercise price (in dollars per share)	$ 3.10	$ 2.74
Balance, weighted average remaining contractual life (Year)	6 years 7 months 20 days	7 years 9 months	7 years 5 months 19 days
Balance, aggregate intrinsic value	$ 405,223	$ 330,831
Granted, number of shares (in shares)	195,000	683,900
Granted, weighted average exercise price (in dollars per share)	$ 2.76	$ 1.08
Exercised, number of shares (in shares)	(36,130)	(26,250)
Exercised, weighted average exercise price (in dollars per share)	$ 1.88	$ 1.34
Forfeited, number of shares (in shares)	(180,592)	(215,218)
Forfeited, weighted average exercise price (in dollars per share)	$ 1.95	$ 1.50
Expired, number of shares (in shares)	(101,155)	(200,367)
Expired, weighted average exercise price (in dollars per share)	$ 3.24	$ 4.82
Balance, number of shares (in shares)	1,664,014	1,786,891	1,544,826
Balance, weighted average exercise price (in dollars per share)	$ 2.07	$ 3.10	$ 2.74
Vested and expected to vest, number of shares (in shares)	1,664,014
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 2.07
Vested and expected to vest, weighted average remaining contractual life (Year)	6 years 7 months 20 days
Vested and expected to vest, aggregate intrinsic value	$ 405,223
Exercisable, number of shares (in shares)	993,041
Exercisable, weighted average exercise price (in dollars per share)	$ 2.41
Exercisable, weighted average remaining contractual life (Year)	5 years 9 months 3 days
Exercisable, aggregate intrinsic value	$ 188,009