Note 5 - Warrants - Warrant Activity (Details) - $ / shares		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020
Balance, number of shares under warrants (in shares)		2,843,284
Balance, number of shares under warrants (in shares)		3,120,147		2,843,284
Weighted Average [Member]
Balance, warrant exercise price (in dollars per share)		$ 8.51
Liability Classified Warrants [Member]
Balance, number of shares under warrants (in shares)	[1]	2,733,645
Balance, weighted average remaining contractual life (Year)		2 years 7 months 6 days		3 years 7 months 6 days
Granted, number of shares under warrants (in shares)		0
Exercised, number of shares under warrants (in shares)		(10,000)
Expired, number of shares under warrants (in shares)		0
Balance, number of shares under warrants (in shares)	[1]	2,723,645		2,733,645
Vested and Exercisable, number of shares under warrants (in shares)		2,723,645
Vested and Exercisable, weighted average remaining contractual life (Year)		2 years 7 months 6 days
Liability Classified Warrants [Member] | Minimum [Member]
Balance, warrant exercise price (in dollars per share)		$ 6.60
Granted, warrant exercise price (in dollars per share)		6.30
Exercised, warrant exercise price (in dollars per share)		6.60
Balance, warrant exercise price (in dollars per share)		6.30		$ 6.60
Vested and Exercisable, warrant exercise price (in dollars per share)		6.30
Liability Classified Warrants [Member] | Maximum [Member]
Balance, warrant exercise price (in dollars per share)		16.80
Granted, warrant exercise price (in dollars per share)		6.30
Exercised, warrant exercise price (in dollars per share)		6.60
Balance, warrant exercise price (in dollars per share)		16.80		16.80
Vested and Exercisable, warrant exercise price (in dollars per share)		16.80
Liability Classified Warrants [Member] | Weighted Average [Member]
Balance, warrant exercise price (in dollars per share)		9.45
Exercised, warrant exercise price (in dollars per share)		6.60
Balance, warrant exercise price (in dollars per share)		9.46	[1]	$ 9.45
Vested and Exercisable, warrant exercise price (in dollars per share)		$ 9.46

[1] If the Company subdivides (by any stock split, stock dividend, recapitalization or otherwise) its outstanding shares of its common stock into a smaller number of shares, the warrant exercise price is proportionately reduced and the number of shares under outstanding warrants is proportionately increased. Additionally, if the Company combines (by combination, reverse stock split or otherwise) its outstanding shares of common stock into a smaller number of shares, the warrant exercise price is proportionately increased and the number of shares under outstanding warrants is proportionately decreased. Also, the Company may voluntarily reduce the warrant exercise price for its warrants issued in March 2019 and February 2017 and may voluntarily extend the contractual term of its warrants issued in February 2017.