Note 2 - Revenue (Details Textual) - USD ($) $ in Thousands		3 Months Ended			12 Months Ended
	Jul. 28, 2023	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2023
Revenue from Contract with Customer, Excluding Assessed Tax		$ 63,474		$ 7,803
Briumvi Ublituximab [Member]
Revenue from Contract with Customer, Excluding Assessed Tax		50,500
Commercialization Agreement With Neuraxpharm [Member]
License and Collaboration Agreements, One-time, Non-refundable Payment	$ 140,000		$ 140,000		$ 140,000
Revenue from Contract with Customer, Including Assessed Tax		400
Consideration Receivable, Performance Obligation		400
Contract with Customer, Asset, after Allowance for Credit Loss		6,500
Commercialization Agreement With Neuraxpharm [Member] | Maximum [Member]
Qualified Sales-based Milestone Revenue	$ 492,500
Product [Member]
Revenue from Contract with Customer, Excluding Assessed Tax		50,488		7,765
Product [Member] | Briumvi Ublituximab [Member]
Gross Net Accruals		15,000
Product Sales, Net Related to Performance Obligations		12,500
Royalty [Member]
Revenue from Contract with Customer, Excluding Assessed Tax		33		$ 0
Royalty [Member] | Maximum [Member]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 100