Note 4 - Warrants - Warrant Activity (Details) - Liability Classified Warrants [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Balance (in shares)	2,723,645
Balance, weighted average remaining contractual life (Year)	2 years 4 months 24 days	2 years 7 months 6 days
Expired, number of shares under warrants (in shares)	(67,349)
Balance (in shares)	2,656,296	2,723,645
Exercisable (in shares)	2,656,296
Exercisable, weighted average remaining contractual life (Year)	2 years 4 months 24 days
Minimum [Member]
Balance, warrant exercise price (in dollars per share)	$ 6.30
Expired, warrant exercise price (in dollars per share)	8.10
Balance, warrant exercise price (in dollars per share)	6.30	$ 6.30
Exercisable, warrant exercise price (in dollars per share)	6.30
Maximum [Member]
Balance, warrant exercise price (in dollars per share)	16.80
Expired, warrant exercise price (in dollars per share)	9.00
Balance, warrant exercise price (in dollars per share)	16.80	16.80
Exercisable, warrant exercise price (in dollars per share)	16.80
Weighted Average [Member]
Balance, warrant exercise price (in dollars per share)	9.46
Expired, warrant exercise price (in dollars per share)	0
Balance, warrant exercise price (in dollars per share)	9.49	$ 9.46
Exercisable, warrant exercise price (in dollars per share)	$ 9.49