Note 10 - Summary of Stock Options - Summary of Option Activity Under All Plans (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / shares shares
Options outstanding (in shares) | shares	40,144
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 456
Options outstanding, weighted average remaining contractual term (Year)	8 years 109 days	7 years 146 days
Options granted (in shares) | shares	23,344
Options granted, weighted average exercise price (in dollars per share) | $ / shares	$ 117.91
Options exercised (in shares) | shares
Options exercised, weighted average exercise price (in dollars per share) | $ / shares
Options canceled (in shares) | shares	(13,017)
Options canceled, weighted average exercise price (in dollars per share) | $ / shares	$ 457.34
Options outstanding (in shares) | shares	50,471	40,144
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 298.99	$ 456
Options outstanding, aggregate intrinsic value | $
Vested and exercisable and expected to vest, end of period (in shares) | shares	48,506
Vested and exercisable and expected to vest, end of period, weighted average exercise price (in dollars per share) | $ / shares	$ 302.18
Vested and exercisable and expected to vest, end of period, weighted average remaining contractual term (Year)	8 years 109 days
Vested and exercisable and expected to vest, end of period, aggregate intrinsic value | $
Vested and exercisable, end of period (in shares) | shares	21,169
Vested and exercisable, end of period, weighted average exercise price (in dollars per share) | $ / shares	$ 397.45
Vested and exercisable, end of period, weighted average remaining contractual term (Year)	7 years 146 days
Vested and exercisable, end of period, aggregate intrinsic value | $