Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2020		Mar. 31, 2019
Series B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	32,667	[1]
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	23,665,905		6,408
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	10,432,654		55,864
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	2,620		4,176

[1] 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. However, under the terms of the Series B Preferred Stock and Warrant Purchase Agreement, as amended, CRG will not convert the Series B preferred stock or exercise the CRG warrants until the Company’s stockholders act to authorize additional number of shares of common stock sufficient to cover the conversion shares.