Note 6 - Stock-based Compensation - Stock Option Activity (Details)	6 Months Ended
	Jun. 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	1,118,700
Granted, weighted-average exercise price (in dollars per share) | $ / shares	$ 0.58
Expired (in shares) | shares	(147)
Expired, weighted-average exercise price (in dollars per share) | $ / shares	$ 142.50
Options outstanding, number (in shares) | shares	1,427,829
Options outstanding, weighted-average exercise price (in dollars per share) | $ / shares	$ 12.53
Options outstanding, weighted-average remaining contractual life (Year)	8 years 328 days
Exercisable (in shares) | shares	660,504
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	$ 26.17
Exercisable, weighted-average remaining contractual life (Year)	8 years 73 days