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Note 10 - Fair Value Measurements - Level of Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Total investment securities |  | $ 337.1 |  | $ 334.2 |
Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | 502.1 |  | 382.4 |
Fair Value, Recurring [Member] |  |  |  |  |
Cash equivalents |  | 821.7 |  | 894.4 |
Total investment securities |  | 839.2 |  | 716.6 |
Other |  | 12.7 |  |  |
Total assets |  | 1,673.6 |  | 1,620.5 |
Long-term debt |  | 383.3 | [1] | 298.0 | [2]
Contingent consideration |  | 30.4 |  |  |
Other |  | 13.6 |  | 20.3 |
Total liabilities |  | 543.0 |  | 435.9 |
Other |  | 13.6 |  | 20.3 |
Fair Value, Recurring [Member] | Derivatives Used in Consolidated Seeded Investment Products [Member] |  |  |  |  |
Other |  |  |  | 9.5 |
Fair Value, Recurring [Member] | Deferred Bonuses Hedge [Member] |  |  |  |  |
Derivative liabilities |  | 115.7 |  | 117.6 |
Fair Value, Recurring [Member] | Other Investment Securities [Member] |  |  |  |  |
Total investment securities |  | 337.1 |  | 334.2 |
Fair Value, Recurring [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | 502.1 |  | 382.4 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |
Cash equivalents |  | 821.7 |  | 894.4 |
Total investment securities |  | 534.4 |  | 529.8 |
Other |  | 0.0 |  |  |
Total assets |  | 1,356.1 |  | 1,424.2 |
Long-term debt |  | 0.0 | [1] | 0.0 | [2]
Contingent consideration |  | 0.0 |  |  |
Other |  | 1.9 |  | 1.7 |
Total liabilities |  | 1.9 |  | 1.7 |
Other |  | 1.9 |  | 1.7 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivatives Used in Consolidated Seeded Investment Products [Member] |  |  |  |  |
Other |  |  |  | 0.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Deferred Bonuses Hedge [Member] |  |  |  |  |
Derivative liabilities |  | 0.0 |  | 0.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Investment Securities [Member] |  |  |  |  |
Total investment securities |  | 273.8 |  | 212.2 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | 260.6 |  | 317.6 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |
Cash equivalents |  | 0.0 |  | 0.0 |
Total investment securities |  | 275.2 |  | 186.7 |
Other |  | 10.2 |  |  |
Total assets |  | 285.4 |  | 195.2 |
Long-term debt |  | 383.3 | [1] | 298.0 | [2]
Contingent consideration |  | 0.0 |  |  |
Other |  | 11.7 |  | 18.6 |
Total liabilities |  | 395.0 |  | 316.6 |
Other |  | 11.7 |  | 18.6 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivatives Used in Consolidated Seeded Investment Products [Member] |  |  |  |  |
Other |  |  |  | 8.5 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Deferred Bonuses Hedge [Member] |  |  |  |  |
Derivative liabilities |  | 0.0 |  | 0.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Investment Securities [Member] |  |  |  |  |
Total investment securities |  | 33.7 |  | 122.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | 241.5 |  | 64.7 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |
Cash equivalents |  | 0.0 |  | 0.0 |
Total investment securities |  | 2.0 |  | 0.1 |
Other |  | 2.5 |  |  |
Total assets |  | 4.5 |  | 1.1 |
Long-term debt |  | 0.0 | [1] | 0.0 | [2]
Contingent consideration |  | 30.4 |  |  |
Other |  | 0.0 |  | 0.0 |
Total liabilities |  | 146.1 |  | 117.6 |
Other |  | 0.0 |  | 0.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivatives Used in Consolidated Seeded Investment Products [Member] |  |  |  |  |
Other |  |  |  | 1.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Deferred Bonuses Hedge [Member] |  |  |  |  |
Derivative liabilities |  | 115.7 |  | 117.6 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investment Securities [Member] |  |  |  |  |
Total investment securities |  | 2.0 |  | 0.0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | 0.0 |  | $ 0.1 |
Fair Value, Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] |  |  |  |  |
Cash equivalents | [3] | 0.0 |  |  |
Total investment securities |  | 27.6 |  |  |
Other |  | 0.0 |  |  |
Total assets |  | 27.6 |  |  |
Long-term debt | [1] | 0.0 |  |  |
Contingent consideration |  | 0.0 |  |  |
Other |  | 0.0 |  |  |
Total liabilities |  | 0.0 |  |  |
Other |  | 0.0 |  |  |
Fair Value, Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Deferred Bonuses Hedge [Member] |  |  |  |  |
Derivative liabilities |  | 0.0 |  |  |
Fair Value, Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Other Investment Securities [Member] |  |  |  |  |
Total investment securities |  | 27.6 |  |  |
Fair Value, Recurring [Member] | Fair Value Measured at Net Asset Value Per Share [Member] | Variable Interest Entity, Primary Beneficiary [Member] |  |  |  |  |
Total investment securities |  | $ 0.0 |  |  |
[1] | Carried at amortized cost in our Consolidated Balance Sheets and disclosed in this table at fair value.
[2] | Carried at amortized cost in our Condensed Consolidated Balance Sheets and disclosed in this table at fair value.
[3] | Certain seeded investment products that do not have a readily determinable fair value have been measured at fair value using the NAV as a practical expedient and have not been categorized in the fair value hierarchy.

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