Note 8 - Common Stock and Common Stock Warrants (Details Textual) - USD ($)							12 Months Ended
	Oct. 27, 2022	Jun. 06, 2022	Apr. 01, 2022	Mar. 31, 2022	Jan. 05, 2022	Feb. 18, 2021	Dec. 31, 2022	Dec. 31, 2021	Sep. 04, 2020
Common Stock, Shares Authorized (in shares)							100,000,000	100,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)							$ 0.0001	$ 0.0001	$ 0.0001
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)			$ 0.0001	$ 0.0001
Common Stock, Shares, Issued (in shares)							59,844,850	21,039,594
Proceeds from Issuance of Common Stock and Warrants, Net				$ 9,300,000
January 2022 Warrants [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.0001
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			4,545,455	4,545,455	4,545,455
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)					$ 2.20
Common Stock, Shares, Issued (in shares)								10,000,000
Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants					$ 10,000,000
Stock Issued During Period, Shares, Exercise of Warrants (in shares)			4,545,455
Pre-funded Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 0.001
Class of Warrant or Right, Issued During Period (in shares)				1,665,025
Class of Warrant or Right, Exercised During Period (in shares)		1,665,025
Common Stock Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	45,178,811			4,850,241
Prefunded Warrant and Common Stock Warrants [Member]
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)	$ 0.9198
Common Stock Warrants 1 [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	0.7949
Common Stock Warrants 2 [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 0.7949
Eshelman Ventures [Member] | Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				860,216
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 2.20
Warrants and Rights Outstanding, Term (Year)				5 years
Institutional Investor [Member] | Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				3,990,025
Institutional Investor [Member] | Common Stock Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				3,990,025
At-the-market Offering [Member]
Stock Issued During Period, Value, New Issues							$ 123,000	$ 9,767,000
Proceeds from Issuance of Common Stock							$ 123,000	$ 9,767,000
At-the-market Offering [Member] | Piper Sandler & Co. and Cantor Fitzgerald & Co. [Member]
Equity Distribution Agreement, Maximum Aggregate Offering Price									$ 60,000,000
Stock Issued During Period, Shares, New Issues (in shares)							54,763	1,432,627
Stock Issued During Period, Value, New Issues							$ 100,000	$ 9,800,000
Securities Purchase Agreement [Member] | Eshelman Ventures [Member]
Stock Issued During Period, Shares, New Issues (in shares)						2,875,000
Shares Issued, Price Per Share (in dollars per share)						$ 7.29
Proceeds from Issuance of Common Stock						$ 20,900,000
Direct Offering [Member]
Stock Issued During Period, Value, New Issues								20,866,000
Proceeds from Issuance of Common Stock and Warrants, Net of Issuance Costs							19,171,000	20,866,000
Direct Offering [Member] | January 2022 Warrants [Member]
Proceeds from Issuance of Common Stock and Warrants, Net of Issuance Costs					$ 9,900,000
Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)				3,185,216
Stock Issued During Period, Value, New Issues							9,291,000
Registered Direct Offering [Member] | Eshelman Ventures [Member]
Stock Issued During Period, Shares, New Issues (in shares)				860,216
Registered Direct Offering [Member] | Institutional Investor [Member]
Stock Issued During Period, Shares, New Issues (in shares)				2,325,000
Common Stock Warrants [Member] | Eshelman Ventures [Member]
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)				$ 2.325
Common Stock Warrants [Member] | Institutional Investor [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				1.88
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)				$ 2.005
Warrants and Rights Outstanding, Term (Year)				5 years
Pre-funded Warrants [Member] | Institutional Investor [Member]
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)				$ 2.004
Private Placement [Member]
Stock Issued During Period, Shares, New Issues (in shares)	45,178,811
Stock Issued During Period, Value, New Issues							24,147,000
Proceeds from Issuance of Common Stock and Warrants, Net of Issuance Costs							$ 40,032,000	$ 0
Shares and Warrants Issued, Price Per Share (in dollars per share)	$ 0.9199
Proceeds from Issuance or Sale of Equity, Total	$ 40,000,000