Note 10 - Stockholders' Equity - Warrant Activity (Details) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Outstanding (in shares)	1,116,484
Outstanding, weighted average exercise price (in dollars per share)	$ 37.27
Outstanding, Weighted Average Remaining Contract Term (Year)	2 years 73 days	178 days
Warrants expired (in shares)	463,236
Warrants expired, weighted average exercise price (in dollars per share)
Warrants exercised (in shares)
Warrants exercised, weighted average exercise price (in dollars per share)
Outstanding (in shares)	653,248	1,116,484
Outstanding, weighted average exercise price (in dollars per share)	$ 6.97	$ 37.27
Exercisable (in shares)	653,248
Exercisable, weighted average exercise price (in dollars per share)	$ 6.97
Exercisable, Weighted Average Remaining Contract Term (Year)	2 years 73 days