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Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 10,695,138 | $ 9,531,050 | $ 7,874,050
Ceded to Other Companies | 1,904,982 | 1,837,267 | 1,585,210
Assumed from Other Companies | 1,213,914 | 1,169,084 | 973,597
Total net premiums written | $ 10,004,070 | $ 8,862,867 | $ 7,262,437
Percentage of Amount Assumed to Net | 12.10% | 13.20% | 13.40%
Insurance |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 10,363,730 | $ 9,220,683 | $ 7,625,981
Ceded to Other Companies | 1,799,639 | 1,727,854 | 1,490,395
Assumed from Other Companies | 220,055 | 250,985 | 211,515
Total net premiums written | $ 8,784,146 | $ 7,743,814 | $ 6,347,101
Percentage of Amount Assumed to Net | 2.50% | 3.20% | 3.30%
Reinsurance & Monoline Excess |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |
Direct Amount | $ 331,408 | $ 310,367 | $ 248,069
Ceded to Other Companies | 105,343 | 109,413 | 94,815
Assumed from Other Companies | 993,859 | 918,099 | 762,082
Total net premiums written | $ 1,219,924 | $ 1,119,053 | $ 915,336
Percentage of Amount Assumed to Net | 81.50% | 82.00% | 83.30%

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