Note 7 - Stockholders' Equity - Summary of Warrant Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Outstanding (in shares)	1,043,667	43,667
Outstanding, weighted average exercise price (in dollars per share)	$ 3.73	$ 3.34
Outstanding, weighted average remaining contractual life (Year)	3 years 9 months	4 years 8 months 8 days	4 years 8 months 19 days
Issued (in shares)	150,418	1,000,000
Issued, weighted average exercise price (in dollars per share)	$ 2.51	$ 3.75
Issued, weighted average remaining contractual life (Year)	4 years 1 month 13 days	4 years 8 months 23 days
Expired (in shares)	(2,000)
Expired, weighted average exercise price (in dollars per share)	$ 10.50
Outstanding as of December 31, 2021 (in shares)	1,192,085	1,043,667	43,667
Outstanding, weighted average exercise price (in dollars per share)	$ 3.57	$ 3.73	$ 3.34
Exercisable (in shares)	1,041,667
Exercisable, weighted average exercise price (in dollars per share)	$ 3.72
Exercisable, weighted average remaining contractual life (Year)	3 years 8 months 12 days