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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] |  |  |  |  |  |
Gross Amount |  | $ 8,540,787 | $ 7,706,832 |  | $ 6,553,910 |
Ceded to other Companies |  | (4,249,258) | (3,734,150) |  | (2,650,352) |
Assumed From Other Companies |  | 6,785,660 | 5,045,655 |  | 3,534,158 |
Net Amount |  | $ 11,077,189 | $ 9,018,337 |  | $ 7,437,716 |
Percentage of Amount Assumed to Net |  | 61.30% | 55.90% |  | 47.50% |
Operating segments | Insurance |  |  |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |  |  |
Gross Amount |  | $ 6,889,358 | $ 5,833,873 |  | $ 4,659,416 |
Ceded to other Companies | [1] | (1,910,222) | (1,719,541) |  | (1,525,655) |
Assumed From Other Companies | [1] | 41,506 | 33,861 |  | 29,146 |
Net Amount |  | $ 5,020,642 | $ 4,148,193 |  | $ 3,162,907 |
Percentage of Amount Assumed to Net |  | 0.80% | 0.80% |  | 0.90% |
Operating segments | Reinsurance |  |  |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |  |  |
Gross Amount |  | $ 395,063 | $ 408,520 |  | $ 305,435 |
Ceded to other Companies | [1] | (2,024,462) | (1,839,556) |  | (1,014,716) |
Assumed From Other Companies | [1] | 6,553,375 | 4,685,410 |  | 3,166,651 |
Net Amount |  | $ 4,923,976 | $ 3,254,374 |  | $ 2,457,370 |
Percentage of Amount Assumed to Net |  | 133.10% | 144.00% |  | 128.90% |
Operating segments | Mortgage |  |  |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |  |  |
Gross Amount |  | $ 1,256,366 | $ 1,213,333 |  | $ 1,192,316 |
Ceded to other Companies | [1] | (322,400) | (246,757) |  | (194,149) |
Assumed From Other Companies | [1] | 198,605 | 294,492 |  | 281,683 |
Net Amount |  | $ 1,132,571 | $ 1,261,068 |  | $ 1,279,850 |
Percentage of Amount Assumed to Net |  | 17.50% | 23.40% |  | 22.00% |
Operating segments | Other |  |  |  |  |  |
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items] |  |  |  |  |  |
Gross Amount |  |  | $ 251,106 |  | $ 396,743 |
Ceded to other Companies |  | $ 0 | (102,763) | [1] | (190,957) | [1]
Assumed From Other Companies | [1] |  | 206,359 |  | 331,803 |
Net Amount |  | $ 0 | $ 354,702 |  | $ 537,589 |
Percentage of Amount Assumed to Net |  |  | 58.20% |  | 61.70% |
[1] | Certain amounts included in the gross premiums written of each segment are related to intersegment transactions and are included in the gross premiums written of each segment. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

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