Note 9 - Stockholders' Equity - Summary of Warrant Activity (Details) - $ / shares	3 Months Ended	12 Months Ended	15 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2021
Outstanding (in shares)		1,043,667	1,043,667
Outstanding, weighted average exercise price (in dollars per share)		$ 3.73	$ 3.73
Outstanding, weighted average remaining contractual life (Year)	4 years 182 days	4 years 255 days
Issued (in shares)			150,418
Issued, weighted average exercise price (in dollars per share)			$ 2.51
Issued, weighted average remaining contractual life (Year)	4 years 328 days
Outstanding (in shares)	1,194,085		1,194,085
Outstanding, weighted average exercise price (in dollars per share)	$ 3.58		$ 3.58
Exercisable (in shares)	43,667		43,667
Exercisable, weighted average exercise price (in dollars per share)	$ 3.34		$ 3.34
Exercisable, weighted average remaining contractual life (Year)	3 years 182 days