Note 5 - Warrants - Outstanding Warrants (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Warrants outstanding (in shares) | shares	327,253
Warrants outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 8.89
Warrants granted (in shares) | shares
Warrants granted, weighted average exercise price (in dollars per share) | $ / shares
Warrants exercised (in shares) | shares	(105,000)
Warrants exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 3.64
Warrants forfeited, canceled (in shares) | shares
Warrants forfeited, canceled, weighted average exercise price (in dollars per share) | $ / shares
Warrants outstanding (in shares) | shares	222,253
Warrants outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 11.37