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Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 11,676,743 | $ 10,695,138 | $ 9,531,050
Ceded to Other Companies | 2,017,539 | 1,904,982 | 1,837,267
Assumed from Other Companies | 1,295,263 | 1,213,914 | 1,169,084
Total net premiums written | $ 10,954,467 | $ 10,004,070 | $ 8,862,867
Percentage of Amount Assumed to Net | 11.80% | 12.10% | 13.20%
Insurance |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 11,310,709 | $ 10,363,730 | $ 9,220,683
Ceded to Other Companies | 1,904,017 | 1,799,639 | 1,727,854
Assumed from Other Companies | 250,429 | 220,055 | 250,985
Total net premiums written | $ 9,657,121 | $ 8,784,146 | $ 7,743,814
Percentage of Amount Assumed to Net | 2.60% | 2.50% | 3.20%
Reinsurance & Monoline Excess |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 366,034 | $ 331,408 | $ 310,367
Ceded to Other Companies | 113,522 | 105,343 | 109,413
Assumed from Other Companies | 1,044,834 | 993,859 | 918,099
Total net premiums written | $ 1,297,346 | $ 1,219,924 | $ 1,119,053
Percentage of Amount Assumed to Net | 80.50% | 81.50% | 82.00%

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