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Transactions With Related Parties (Details) - USD ($) $ in Thousands | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2022 | Mar. 31, 2021 | Dec. 31, 2021 | Jul. 01, 2021 | Jan. 01, 2021 | Dec. 31, 2020
Related Party Transaction [Line Items] |  |  |  |  |  |
Premiums ceded | $ 1,166,635 | $ 888,749 |  |  |  |
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses | 5,941,000 | $ 4,041,076 | $ 5,880,735 |  |  | $ 4,500,802
Reinsurance balances payable | 1,510,906 |  | $ 1,583,253 |  |  |
Greysbridge Holdings Ltd |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Percentage ownership |  |  |  | 40.00% |  |
Kelso And Company | Greysbridge Holdings Ltd |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Percentage ownership |  |  |  | 30.00% |  |
Warburg Pincus LLC | Greysbridge Holdings Ltd |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Percentage ownership |  |  |  | 30.00% |  |
Operating affiliates | Premia Holdings Ltd |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Legacy business, amount of liabilities transferred |  |  |  |  | $ 380,000 |
Operating affiliates | Somers Holdings Ltd |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Premiums ceded | 220,500 |  |  |  |  |
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses | 933,700 |  |  |  |  |
Reinsurance balances payable | 324,400 |  |  |  |  |
Senior notes, face amount | $ 35,000 |  |  |  |  |
Senior notes, stated percentage | 6.50% |  |  |  |  |
Operating affiliates | Somers Holdings Ltd | Non-cumulative preferred shares |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |
Percentage ownership | 6.60% |  |  |  |  |

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