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Fair Value Measurements - Additional Information - Narrative (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2024 USD ($) quotesPerInvestment | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($) quotesPerInvestment | Sep. 30, 2023 USD ($) | Dec. 31, 2023 USD ($) quotesPerInvestment | Dec. 31, 2022 USD ($) quotesPerInvestment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Quotes per fixed income investment | quotesPerInvestment | 3.3 |  | 3.3 |  | 2.9 | 2.9
Assets | Recurring | Level 3 |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |
Transfers in/(out) | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | $ 5.3 | $ 0.0
Settlements and sales | $ (114.5) | $ (76.4) | $ (166.9) | $ (134.8) | $ (137.2) | $ (147.4)

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