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Reinsurance (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |
Percentage of ceded earned premiums to gross earned premiums | 45.00% | 40.00% | 42.00% | 38.00%
Percentage of assumed earned premiums to net earned premiums | 44.00% | 35.00% | 33.00% | 29.00%
Program services and other fronting [Member] |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |
Gross losses and loss adjustment expenses | $ 975.0 | $ 743.8 | $ 2,200.0 | $ 1,800.0

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