Note 12 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Options outstanding, beginning of period (in shares) | shares	10,087,678
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 2.22
Options outstanding, weighted average remaining contractual term (Year)	9 years 36 days	9 years 328 days
Options outstanding, aggregate intrinsic value | $		$ 3,928,715
Options granted (in shares) | shares	1,018,000
Options granted, weighted average exercise price (in dollars per share) | $ / shares	$ 0.70
Options exercised (in shares) | shares
Options exercised, weighted average exercise price (in dollars per share) | $ / shares
Options canceled (in shares) | shares	(1,350,224)
Options canceled, weighted average exercise price (in dollars per share) | $ / shares	$ 3.01
Options outstanding, end of period (in shares) | shares	9,755,454	10,087,678
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 1.96	$ 2.22
Vested and exercisable and expected to vest, end of period (in shares) | shares	9,047,744
Vested and exercisable and expected to vest, end of period, weighted average exercise price (in dollars per share) | $ / shares	$ 2.03
Vested and exercisable and expected to vest, end of period, weighted average remaining contractual term (Year)	9 years 36 days
Vested and exercisable and expected to vest, end of period, aggregate intrinsic value | $
Vested and exercisable, end of period (in shares) | shares	1,969,073
Vested and exercisable, end of period, weighted average exercise price (in dollars per share) | $ / shares	$ 5.19
Vested and exercisable, end of period, weighted average remaining contractual term (Year)	8 years 255 days
Vested and exercisable, end of period, aggregate intrinsic value | $