Note 6 - Stock-based Compensation - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Options outstanding, number (in shares) | shares	309,276
Options outstanding, weighted-average exercise price (in dollars per share) | $ / shares	$ 55.78
Granted (in shares) | shares	1,731,100
Granted, weighted-average exercise price (in dollars per share) | $ / shares	$ 0.66
Expired (in shares) | shares	(172)
Expired, weighted-average exercise price (in dollars per share) | $ / shares	$ 142.50
Options outstanding, number (in shares) | shares	2,040,204
Options outstanding, weighted-average exercise price (in dollars per share) | $ / shares	$ 9.01
Options outstanding, weighted-average remaining contractual life (Year)	9 years 36 days
Exercisable (in shares) | shares	992,779
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	$ 17.65
Exercisable, weighted-average remaining contractual life (Year)	8 years 146 days