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Agreements and Transactions with Related Parties - 2015 Activity (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023 | Dec. 31, 2015
Agreements and Transactions with Related Parties |  |  |  |  |  |
Indirect ownership percentage |  |  | 12.30% |  | 12.30% |
Residential mortgage banking business | Other Related Party Transactions | Related Party | Noncontrolling Interest |  |  |  |  |  |
Agreements and Transactions with Related Parties |  |  |  |  |  |
Indirect ownership percentage |  |  | 12.30% |  |  |
Gain (loss) on investment | $ (1.0) | $ (1.3) | $ (0.1) | $ 1.3 |  |
Distribution received |  | $ 7.5 | $ 7.7 | $ 15.0 |  |
Residential mortgage banking business | Other Related Party Transactions | Related Party | ACM |  |  |  |  |  |
Agreements and Transactions with Related Parties |  |  |  |  |  |
Noncontrolling interest in equity method investment acquired (as a percent) |  |  |  |  |  | 50.00%
ACM | Residential mortgage banking business | Other Related Party Transactions | Related Party |  |  |  |  |  |
Agreements and Transactions with Related Parties |  |  |  |  |  |
Acquisition purchase price |  |  |  |  |  | $ 9.6

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