Note 10 - Stockholders' Equity - Summary of Warrant Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Outstanding (in shares)	1,043,667
Outstanding, weighted average exercise price (in dollars per share)	$ 3.73
Outstanding, weighted average remaining contractual life (Year)	4 years 3 months 18 days	4 years 8 months 12 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 2 months 12 days
Expired (in shares)	(2,000)
Expired, weighted average exercise price (in dollars per share)	$ 10.50
Outstanding (in shares)	1,192,085	1,043,667
Outstanding, weighted average exercise price (in dollars per share)	$ 3.57	$ 3.73
Exercisable (in shares)	41,667
Exercisable, weighted average exercise price (in dollars per share)	$ 3.00
Exercisable, weighted average remaining contractual life (Year)	3 years 4 months 24 days