Note 7 - Common Stock and Common Stock Warrants (Details Textual) - USD ($)				3 Months Ended				6 Months Ended
	Jun. 06, 2022	Mar. 31, 2022	Feb. 18, 2021	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Apr. 01, 2022	Dec. 31, 2021	Sep. 04, 2020
Common Stock, Shares Authorized (in shares)				100,000,000				100,000,000			100,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.0001				$ 0.0001			$ 0.0001	$ 0.0001
Proceeds from Issuance of Common Stock and Warrants, Net		$ 9,300,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 0.0001			$ 0.0001					$ 0.0001
Pre-funded Warrants [Member]
Class of Warrant or Right, Issued During Period (in shares)		1,665,025
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 0.001			$ 0.001
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)		4,850,241			4,850,241
Eshelman Ventures [Member] | Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		860,216			860,216
Warrants and Rights Outstanding, Term (Year)		5 years			5 years
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 2.20			$ 2.20
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			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			3,990,025
At-the-market Offering [Member]
Stock Issued During Period, Value, New Issues					$ 123,000	$ 1,816,000	$ 7,034,000
Proceeds from Issuance of Common Stock								$ 123,000	$ 8,850,000
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)				0	54,763
Stock Issued During Period, Value, New Issues				$ 0	$ 100,000
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
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			$ 2.325
Common Stock Warrants [Member] | Institutional Investor [Member]
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)		$ 2.005			$ 2.005
Warrants and Rights Outstanding, Term (Year)		5 years			5 years
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 1.88			$ 1.88
Pre-funded Warrants [Member] | Institutional Investor [Member]
Class of Warrant or Right, Purchase Price of Warrants or Rights (in dollars per share)		$ 2.004			$ 2.004