Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019
Series A Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)		[1]	185,218
Series B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	2,341,111	[2]	2,070,458
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	1,728,725		2,473,785
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	986,399		1,008,833
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	394		277

[1] Each share of Series A convertible preferred stock was convertible at any time at the holder's option into one share of common stock. In December 2020, the Company filed a Certificate of Elimination with the Delaware Secretary of State with respect to the authorized shares of Series A convertible preferred stock. As of December 31, 2020, all Series A convertible preferred stock had been converted into common stock and there were no remaining shares outstanding.

[2] As of December 31, 2020 and 2019, a total of 35,819 and 31,678 shares of Series B convertible preferred stock were outstanding and convertible into 2,341,111 and 2,70,458 shares of common stock, respectively. 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-65.36 per share determined by dividing the Series B liquidation amount of $1,000 per share by the Series B conversion price of $15.30 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.