Note 8 - Stockholders' Equity - Warrant Activity (Details)	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Outstanding (in shares) | shares	1,726,523
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 29.88
Warrants granted(1) (in shares) | shares	444,445	[1]
Warrants granted(1) (in dollars per share) | $ / shares	$ 0.10	[1]
Warrants expired (in shares) | shares	(19,637)
Warrants expired, weighted average exercise price (in dollars per share) | $ / shares	$ 417
Warrants exercised (in shares) | shares	(416,500)
Warrants exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 0.10
Outstanding (in shares) | shares	1,734,831
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 25.02
Exercisable (in shares) | shares	1,664,978
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 22.72

[1] See Footnote 1 of the Notes to the Condensed Consolidated Financial Statements.