Note 2 - Revenue (Details Textual) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Jul. 28, 2023	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2024	Mar. 31, 2024
Commercialization Agreement With Neuraxpharm [Member]
License and Collaboration Agreements, One-time, Non-refundable Payment	$ 140.0		$ 140.0	$ 140.0
Royalty Percentage on Net Product Sales	30.00%
Revenue from Contract with Customer, Including Assessed Tax					$ 1.1
Consideration Receivable, Performance Obligation		$ 0.4			0.4
Contract with Customer, Liability		7.0			7.0
Commercialization Agreement With Neuraxpharm [Member] | Maximum [Member]
Qualified Sales-based Milestone Revenue	$ 492.5
Product [Member] | Briumvi Ublituximab [Member]
Gross Net Accruals		21.6			21.6
Revenue from Contract with Customer, Including Assessed Tax		0.7
Product Sales, Net Related to Performance Obligations						$ 12.5
Royalty [Member] | Maximum [Member]
Revenue from Contract with Customer, Including Assessed Tax					$ 0.2
Royalty [Member] | Minimum [Member]
Revenue from Contract with Customer, Including Assessed Tax		$ 0.1