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Reinsurance (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |
Percentage of ceded earned premiums to gross earned premiums | 40.00% | 40.00% | 38.00% | 38.00%
Percentage of assumed earned premiums to net earned premiums | 35.00% | 32.00% | 29.00% | 28.00%
Underwriting [Member] |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |
Gross losses and loss adjustment expenses | $ 1,684,389 | $ 1,423,526 | $ 4,552,926 | $ 3,760,566
Ceded losses | 278,945 | 238,220 | 786,876 | 544,109
Program services and other fronting [Member] |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |
Gross losses and loss adjustment expenses | 743,800 | 1,300,000 | 1,800,000 | 2,300,000
Ceded losses | $ (744,900) | $ (1,330,700) | $ (1,835,900) | $ (2,321,200)

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