Note 10 - Stockholders' Equity - Warrant Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 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)	1 year 10 months 24 days	5 months 26 days
Warrants expired (in shares)	463,236
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)	1 year 10 months 24 days