Note 10 - Stockholders' Equity - Option Activity for Stock Option Plans (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) $ / shares shares
Outstanding, options (in shares) | shares	889,636
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 8.57
Forfeited, options (in shares) | shares
Forfeited, weighted average exercise price, options (in dollars per share) | $ / shares
Outstanding, options (in shares) | shares	889,636
Outstanding, weighted average exercise price, options (in dollars per share) | $ / shares	$ 8.57
Outstanding, weighted average remaining contractual life, options (Year)	8 years 182 days
Outstanding, aggregate intrinsic value, options | $
Vested and expected to vest, options (in shares) | shares	631,053
Vested and expected to vest, weighted average exercise price, options (in dollars per share) | $ / shares	$ 9.54
Vested and expected to vest, weighted average remaining contractual life, options (Year)	8 years 109 days
Vested and expected to vest, aggregate intrinsic value, options | $
Exercisable, options (in shares) | shares	230,836
Exercisable, weighted average exercise price, options (in dollars per share) | $ / shares	$ 15.21
Exercisable, weighted average remaining contractual life, options (Year)	7 years 73 days
Exercisable, aggregate intrinsic value, options | $