Note 3 - Investments - Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Investments, net	$ (9.9)	$ (107.5)
Seeded Investment Products [Member]
Purchases and settlements	(41.1)	(142.3)
Sales, settlements and maturities	3.0	19.1
Investments, net	(38.1)	(123.2)
Securities Investment [Member]
Purchases and settlements	(65.7)	(113.2)
Sales, settlements and maturities	55.8	5.7
Investments, net	$ (9.9)	$ (107.5)