Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021
Series B Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	[1]	2,814,967	2,489,542
Series C Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	[2]	0	0
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)		9,793,599	9,793,599
Share-Based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)		4,124,009	3,188,628
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)		674,000	684,000
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)		228	232

[1] As of March 31, 2022 and 2021, a total of 41,767 and 36,937 shares of Series B convertible preferred stock were outstanding and convertible into 2,729,869 and 2,414,283 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 LP (“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.

[2] Each share of Series C convertible preferred stock was convertible at any time at the holder's option into one share of common stock. All Series C convertible preferred stock had been converted into common stock and there were no remaining shares outstanding. In March 2022, the Company filed a Certificate of Elimination with the Delaware Secretary of State with respect to the authorized shares of Series C convertible preferred stock.