Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019
Series B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	22,702,614	[1]
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	17,710,876		5,549
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	9,755,454		50,471
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	2,217		3,432

[1] As of September 30, 2020, a total of 34,735 shares of Series B convertible preferred stock were outstanding and are convertible into 22,702,614 shares of common stock. Each share of Series B convertible 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.