Note 6 - Stockholders' Equity - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Outstanding, number of units, balance (in shares)	1,666,797	1,206,709
Outstanding, weighted average exercise price, beginning balance (in dollars per share)	$ 13.96	$ 17.93
Outstanding, weighted average remaining contractual term (Year)	7 years 306 days	7 years 80 days	6 years 354 days
Granted, number of units (in shares)	1,511,000	714,350
Granted, weighted average exercise price (in dollars per share)	$ 4.03	$ 5.76
Cancelled, number of units (in shares)	(198,750)	(254,262)
Cancelled, weighted average exercise price (in dollars per share)	$ 7.52	$ 9.78
Outstanding, aggregate intrinsic value	$ 2,074,150	$ 91,475
Outstanding, number of units, balance (in shares)	2,979,047	1,666,797	1,206,709
Outstanding, weighted average exercise price, balance (in dollars per share)	$ 9.35	$ 13.96	$ 17.93
Exercisable, number of units (in shares)	1,131,314
Exercisable, weighted average exercise price (in dollars per share)	$ 17.34
Exercisable, weighted average remaining contractual term (Year)	5 years 138 days
Exercisable, aggregate intrinsic value	$ 15,360