Note 6 - Common Stock Warrants - Summary of Warrant Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Warrants and Rights Note Disclosure [Abstract]
Warrants outstanding, balance (in shares)	7,181,741
Warrants outstanding, weighted average exercise price (in dollars per share)	$ 2.74	$ 5.96
Warrants outstanding, December 31, 2021	4 years 9 months 14 days	4 years 5 months 12 days
Class of warrant or right, issued during period (in shares)	6,115,491
Granted, weighted average exercise price (in dollars per share)	$ 0.85
Granted, weighted average remaining contractual life	5 years 2 months 26 days
Exercised (in shares)	(3,994,302)
Exercised, weighted average exercise price	$ 3.88
Exercised, weighted average remaining contractual life	4 years 1 month 9 days
Forfeited, expired or cancelled (in shares)	(89,922)
Forfeited, expired, or cancelled, weighted average exercise price	$ 80.72
Warrants outstanding, balance (in shares)	9,213,008	7,181,741