Note 8 - Warrants - Summary of Warrant Activity (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Outstanding, number of shares (in shares) | shares	3,959,005
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 4.33
Exercised, number of shares (in shares) | shares	(2,000)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 4.75
Outstanding, number of shares (in shares) | shares	3,957,005
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 4.33