Note 12 - Net Loss Per Share Attributable to Common Stockholders - Summary of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)	15,030,424	989,409	9,807,084	1,363,016
Share-based Payment Arrangement, Option [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)	1,965,910	978,495	1,466,495	802,885
Warrant [Member] | Convertible Preferred Stock [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)				1,191
Warrant [Member] | Common Stock [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)	13,064,514	10,914	8,340,589	9,195
Series B and C Convertible Preferred Stock, Including Cumulative Dividends [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)				285,797
Series A Convertible Preferred Stock [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)				16,391
Convertible Debt Securities [Member]
Potentially dilutive securities excluded from denominator of the diluted earnings per share computation (in shares)				247,557