Note 1 - Business and Basis of Presentation (Details Textual)	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 18, 2014 USD ($)
Number of Subsidiaries	1
Upfront License Fee	$ 7,000,000.0
Milestone Payments Maximum Amount	287,300,000			$ 187,500,000
Research and Development in Process	7,000,000	$ 0	$ 0
Net Income (Loss) Attributable to Parent, Total	2,000	(29,126,000)	(59,995,000)
Net Cash Provided by (Used in) Operating Activities, Total	(15,827,000)	$ 20,650,000	$ 773,000
Cash, Cash Equivalents, and Marketable Securities	$ 81,100,000