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Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 12,904,893 | $ 11,676,743 | $ 10,695,138
Ceded to Other Companies | 2,238,995 | 2,017,539 | 1,904,982
Assumed from Other Companies | 1,306,198 | 1,295,263 | 1,213,914
Total net premiums written | $ 11,972,096 | $ 10,954,467 | $ 10,004,070
Percentage of Amount Assumed to Net | 10.90% | 11.80% | 12.10%
Insurance |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 12,417,129 | $ 11,209,325 | $ 10,193,154
Ceded to Other Companies | 2,112,582 | 1,900,560 | 1,796,845
Assumed from Other Companies | 245,003 | 251,768 | 212,719
Total net premiums written | $ 10,549,550 | $ 9,560,533 | $ 8,609,028
Percentage of Amount Assumed to Net | 2.30% | 2.60% | 2.50%
Reinsurance & Monoline Excess |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 487,764 | $ 467,418 | $ 501,984
Ceded to Other Companies | 126,413 | 116,979 | 108,137
Assumed from Other Companies | 1,061,195 | 1,043,495 | 1,001,195
Total net premiums written | $ 1,422,546 | $ 1,393,934 | $ 1,395,042
Percentage of Amount Assumed to Net | 74.60% | 74.90% | 71.80%

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