Note 7 - Stockholders' Equity - Option Activity for Stock Option Plans (Details)	9 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares
Outstanding, options (in shares) | shares	291,807
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 13.96
Granted, options (in shares) | shares	615,500
Granted, weighted average exercise price, options (in dollars per share) | $ / shares	$ 5.92
Forfeited, options (in shares) | shares	(15,158)
Forfeited, weighted average exercise price, options (in dollars per share) | $ / shares	$ 5.13
Outstanding, options (in shares) | shares	892,149
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 8.57
Outstanding, weighted average remaining contractual life, options (Year)	8 years 363 days
Outstanding, aggregate intrinsic value, options | $
Vested and expected to vest, options (in shares) | shares	565,836
Vested and expected to vest, weighted average exercise price, options (in dollars per share) | $ / shares	$ 9.91
Vested and expected to vest, weighted average remaining contractual life, options (Year)	8 years 268 days
Vested and expected to vest, aggregate intrinsic value, options | $
Exercisable, options (in shares) | shares	184,137
Exercisable, weighted average exercise price, options (in dollars per share) | $ / shares	$ 17.05
Exercisable, weighted average remaining contractual life, options (Year)	7 years 242 days
Exercisable, aggregate intrinsic value, options | $