Note 7 - Restructured Debt Liability (Details Textual) - USD ($) $ / shares in Units, $ in Millions	Oct. 27, 2017	Mar. 31, 2023	Dec. 31, 2022
Liability for Contingent Milestone Payment, Noncurrent		$ 15.0	$ 15.0
Deerfield Loan [Member] | Exchange and Termination Agreement [Member] | Deerfield Management, L.P. [Member]
Extinguishment of Debt, Amount	$ 25.0
Class of Warrant or Right, Number of Warrants Cancelled (in shares)	167
Class of Warrant or Right, Exercise Price of Cancelled Warrants (in dollars per share)	$ 118,020.00
Repayments of Long-term Debt, Total	$ 2.5
Stock Issued During Period, Shares, Cancellation of Debt and Warrant Obligations (in shares)	474
Stock Issued During Period, Shares, Cancellation of Debt and Warrant Obligations, Percentage of Fully-diluted Shares Outstanding	2.00%
Liability for Contingent Milestone Payment, Noncurrent	$ 15.0	$ 15.0	$ 15.0