Note 5 - Equity - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Outstanding, number of shares (in shares)	4,535,681	2,628,749
Outstanding, weighted average exercise price (in dollars per share)	$ 3.31	$ 1.31
Options granted, number of shares (in shares)	1,744,300	2,034,525
Options granted, weighted average exercise price (in dollars per share)	$ 1.48	$ 6.21
Options exercised, number of shares (in shares)
Options expired, number of shares (in shares)	(297,058)	(127,593)
Outstanding, number of shares (in shares)	5,982,923	4,535,681
Outstanding, weighted average exercise price (in dollars per share)	$ 2.66	$ 3.31