Note 6 - Stock-based Compensation - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) $ / 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	873,500
Granted, weighted-average exercise price (in dollars per share) | $ / shares	$ 0.47
Expired (in shares) | shares	(147)
Expired, weighted-average exercise price (in dollars per share) | $ / shares	$ 142.50
Options outstanding, number (in shares) | shares	1,182,629
Options outstanding, weighted-average exercise price (in dollars per share) | $ / shares	$ 14.91
Options outstanding, weighted-average remaining contractual life (Year)	9 years
Options outstanding, aggregate intrinsic value | $
Exercisable (in shares) | shares	560,524
Exercisable, weighted-average exercise price (in dollars per share) | $ / shares	$ 30.60
Exercisable, weighted-average remaining contractual life (Year)	8 years 73 days
Exercisable, aggregate intrinsic value | $