Note 8 - Common Stock Warrants - Summary of Warrant Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Warrants outstanding, balance (in shares)	195,712
Warrants outstanding, weighted average exercise price (in dollars per share)	$ 5.96	$ 21.20
Warrants outstanding, December 31, 2020 (Year)	4 years 5 months 12 days	6 years 7 months 6 days
Class of warrant or right, issued during period (in shares)	7,572,191
Granted, weighted average exercise price (in dollars per share)	$ 3.86
Granted, weighted average remaining contractual life	4 years 7 months 17 days
Seneca warrants (in shares)	749,792
Seneca warrants, weighted average exercise price	$ 21.07
Seneca warrants, weighted average remaining contractual life	2 years 6 months 29 days
Exercised (in shares)	(1,309,266)
Exercised, weighted average exercise price	$ 3.88
Exercised, weighted average remaining contractual life	4 years 10 months 9 days
Settled (in shares)	(20,313)
Settled, weighted average exercise price	$ 57.46
Settled, weighted average remaining contractual life	2 years 5 months 4 days
Forfeited, expired or cancelled (in shares)	(6,375)
Forfeited, expired, or cancelled, weighted average exercise price	$ 18.37
Forfeited, expired or cancelled, weighted average remaining contractual life	2 years 8 months 26 days
Warrants outstanding, balance (in shares)	7,181,741	195,712