Note 4 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
|
| Investment gains (losses), net | $ (5.5) | $ 22.5 |
| Seeded Investment Products and Hedges, Net [Member] | ||
| Investment gains (losses), net | 5.8 | 11.9 |
| Third-party Ownership Interests in Seeded Investment Products [Member] | ||
| Investment gains (losses), net | (3.3) | 10.5 |
| Equity Method Investments [Member] | ||
| Investment gains (losses), net | (1.7) | (1.4) |
| Other Security Investments [Member] | ||
| Investment gains (losses), net | $ (6.3) | $ 1.5 |