Note 5 - Share-based Compensation - Stock Option Activity (Details) - USD ($)		3 Months Ended
	Dec. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Outstanding, shares (in shares)		4,774,215	5,425,040
Outstanding, weighted average exercise price (in dollars per share)		$ 3.04
Weighted-average remaining contractual term, outstanding (Year)	6 years 1 month 20 days	6 years 5 months 23 days
Aggregate intrinsic value, outstanding	$ 8,413,444	$ 3,931,706
Granted, shares (in shares)		715,825
Granted, weighted average exercise price (in dollars per share)		$ 4.81
Exercised, shares (in shares)		(35,000)
Exercised, weighted average exercise price (in dollars per share)		$ 1.21
Expired, shares (in shares)		(30,000)
Expired, weighted average exercise price (in dollars per share)		$ 6.87
Outstanding, weighted average exercise price (in dollars per share)	$ 3.04	3.27
Exercisable, shares (in shares)	4,070,223
Exercisable, weighted average exercise price (in dollars per share)		$ 2.79
Weighted-average remaining contractual term, exercisable (Year)		5 years 7 months 9 days
Aggregate intrinsic value, exercisable		$ 3,827,242