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Fair Value Measurements - Additional Information - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2024 USD ($) quotesPerInvestment | Dec. 31, 2023 USD ($) quotesPerInvestment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Quotes per fixed income investment | quotesPerInvestment | 3.0 | 2.9
Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Privately-held Investments, at fair value | $ 286.8 |
Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Privately-held Investments, at fair value | 286.8 |
Total, Privately-held Investments | 311.0 |
Assets | Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Transfers out of Level 3 | 0.0 | $ 12.1
Transfers in/(out) | 0.0 | 5.3
Settlements and sales | $ (239.7) | (137.2)
Equity Securities | Assets | Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Transfers out of Level 3 |  | (6.6)
Transfers in/(out) |  | 0.0
Settlements and sales |  | $ 0.0

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