Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018
Series A Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	1,852,173	[1]
Series B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	31,678	[2]
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	24,737,618		6,408
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	10,087,678		40,195
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	2,620		575

[1] Each share of Series A preferred stock is convertible at any time at the holder's option into one share of common stock.

[2] Each share of Series B preferred stock is convertible at the holder's option into shares of common stock at a conversion ratio of 1-for-653.59 per share determined by dividing the Series B liquidation amount of $1,000 per share by the Series B conversion price of $1.53 per share.