Note 4 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Investment gains, net | $ 52.6 | $ 6.4 | $ 47.1 | $ 28.9 |
| Seeded Investment Products and Hedges, Net [Member] | ||||
| Investment gains, net | 13.8 | 4.6 | 19.6 | 16.5 |
| Third-party Ownership Interests in Seeded Investment Products [Member] | ||||
| Investment gains, net | 36.7 | 3.8 | 33.4 | 14.3 |
| Equity Method Investments [Member] | ||||
| Investment gains, net | (1.6) | (2.1) | (3.3) | (3.5) |
| Other Security Investments [Member] | ||||
| Investment gains, net | $ 3.7 | $ 0.1 | $ (2.6) | $ 1.6 |