Note 1 - Organization (Details Textual) - USD ($)				1 Months Ended		12 Months Ended
	Aug. 04, 2022	Jan. 14, 2022	Feb. 02, 2021	Aug. 31, 2022	Feb. 28, 2021	Dec. 31, 2022	May 20, 2022	Dec. 31, 2021
Retained Earnings (Accumulated Deficit), Total						$ (402,376,000)		$ (384,753,000)
Cash and Cash Equivalents, at Carrying Value, Total						$ 14,603,000		$ 19,497,000
Share Price						$ 1.09
Preferred Stock, Par or Stated Value Per Share						$ 0.001		$ 0.001
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						8,255,148		132,265
Class of Warrant or Right, Outstanding						51,185,758		26,456,895
Common Stock, Par or Stated Value Per Share (in dollars per share)						$ 0.001		$ 0.001
Common Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		807,500
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 9.60
Warrants and Rights Outstanding, Term		5 years
Placement agent warrants issued in the January 2022 financing [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		66,500				66,500
Class of Warrant or Right, Outstanding						1,330,000
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 10.00				$ 10.00
Warrants and Rights Outstanding, Term		5 years
Registered Direct Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	784,019
Pre-funded Warrants [Member]
Class of Warrant or Right, Outstanding						622,000
Series A Preferred Investment Options [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				2,853,883
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 1.502
Warrants and Rights Outstanding, Term				5 years 6 months
Series B Preferred Investment Options [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				2,853,883
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 1.502
Warrants and Rights Outstanding, Term				2 years
Placement Agent Preferred Investment Options [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				171,233
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 2.19
Warrants and Rights Outstanding, Term				5 years
Series D Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share		$ 0.001
Series D Preferred Stock [Member] | Common Warrants [Member]
Class of Warrant or Right, Outstanding		807,500
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 9.60
Warrants and Rights Outstanding, Term		5 years
Series D Preferred Stock [Member] | Placement agent warrants issued in the January 2022 financing [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		66,500
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 10.00
Warrants and Rights Outstanding, Term		5 years
August 2022 Public Offering [Member]
Proceeds from Issuance or Sale of Equity, Net				$ 4,400,000
The Market Offering Agreement (the “ATM Agreement”) [Member]
Proceeds from Issuance or Sale of Equity, Net						$ 800,000
January 2022 Public Offering [Member]
Proceeds from Issuance or Sale of Equity, Net		$ 6,700,000				$ 6,700,000
January 2022 Public Offering [Member] | Series D Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues		7,600
Preferred Stock, Par or Stated Value Per Share		$ 1,000
Preferred Stock, Convertible, Conversion Price		$ 8.00
February 2021 Public Offering [Member]
Proceeds from Issuance or Sale of Equity, Net			$ 13,000,000.0		$ 13,000,000.0
Stock Issued During Period, Shares, New Issues			500,000
Share Price			$ 28.80
August 2022 Purchase Agreement [Member]
Stock Issued During Period, Shares, New Issues	700,000
Sale of Stock, Number of Shares (in shares)	1,484,019
Shares Issued, Price Per Share (in dollars per share)	$ 1.752
Proceeds from Issuance or Sale of Equity, Total	$ 4,400,000
Private Placement [Member]
Stock Issued During Period, Shares, New Issues	1,369,864
Shares Issued, Price Per Share (in dollars per share)	$ 1.752
Private Placement [Member] | Registered Direct Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,369,864
Common Stock in June, 2022 [Member]
Stock Issued During Period, Shares, New Issues						585,603
Shares Issued, Price Per Share (in dollars per share)						$ 1.67
Proceeds from Issuance or Sale of Equity, Total						$ 1,000,000.0
Common Stock, Par or Stated Value Per Share (in dollars per share)							$ 0.001
Share Offering Agreement, Aggregate Offering							$ 7,000,000
Commission Percentage							3.00%
Payments of Stock Issuance Costs						$ 29,000