Note 8 - Common Stock (Details Textual) - USD ($)			12 Months Ended
	Feb. 18, 2021	Apr. 08, 2020	Dec. 31, 2021	Dec. 31, 2020	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
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
Private Placement [Member]
Stock Issued During Period, Value, New Issues				$ 4,922,000
Payments of Stock Issuance Costs				78,000
Private Placement [Member] | Eshelman Ventures [Member]
Stock Issued During Period, Shares, New Issues (in shares)		931,098
Stock Issued During Period, Value, New Issues		$ 5,000,000.0
Payments of Stock Issuance Costs		$ 78,000
At-the-market Offering [Member]
Proceeds from Issuance of Common Stock			$ 9,767,000	$ 2,266,000
Stock Issued During Period, Value, New Issues			$ 9,767,000
At-the-market Offering [Member] | Piper Sandler & Co. and Cantor Fitzgerald & Co. [Member]
Stock Issued During Period, Shares, New Issues (in shares)			1,432,627	377,400
Stock Issued During Period, Value, New Issues			$ 9,800,000	$ 2,300,000
Equity Distribution Agreement, Maximum Aggregate Offering Price					$ 60,000,000