Note 12 - Stockholders' Equity - Warrant Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Outstanding (in shares)	1,116,484	1,716,066
Outstanding, weighted average exercise price (in dollars per share)	$ 37.27	$ 25.23
Outstanding, Weighted Average Remaining Contract Term (Year)	1 year 4 months 24 days	5 months 26 days	1 year 6 months 25 days
Warrants exercised (in shares)		(599,582)
Warrants exercised, weighted average exercise price (in dollars per share)		$ 2.81
Outstanding (in shares)	653,248	1,116,484	1,716,066
Outstanding, weighted average exercise price (in dollars per share)	$ 6.97	$ 37.27	$ 25.23
Exercisable (in shares)		1,046,631
Exercisable, weighted average exercise price (in dollars per share)		$ 34.42
Exercisable, Weighted Average Remaining Contract Term (Year)		6 months 14 days
Warrants expired/canceled (in shares)	(463,236)
Warrants expired/canceled (in dollars per share)	$ 80