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Investment Information - Investments in operating affiliates (Details) € / shares in Units, $ / shares in Units, $ in Thousands, € in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2021 EUR (€) € / shares | Jul. 01, 2021 $ / shares
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Investment in operating affiliates | $ 964,604 | $ 1,135,655 |  |  |
Income (loss) from operating affiliates | $ 73,891 | $ 264,693 | $ 16,766 |  |
Coface |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage ownership | 29.90% | 29.50% |  | 29.50% |
Investment in affiliate, price per share | € / shares |  |  |  | € 9.95 |
Equity method investment, aggregate cost |  | $ 546,000 |  | € 453 |
Operating affiliate gain on acquisition |  | 74,500 |  |  |
Operating affiliates , deferred gain on acquisition |  | 36,000 |  |  |
Operating affiliates, deferred gain on acquisition, amortization period | 5 years |  |  |  |
Investment in operating affiliates | $ 562,900 | 630,500 |  |  |
Coface | Issued Shares Excluding Treasury Stock |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage ownership | 30.10% |  |  |  |
Greysbridge Holdings Ltd |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage ownership |  |  |  |  | 40.00%
Investment in affiliate, price per share | $ / shares |  |  |  |  | $ 35.00
Equity method investment, aggregate cost |  | 278,900 |  |  |
Operating affiliate gain on acquisition |  | 95,700 |  |  |
Investment in operating affiliates | $ 305,600 | 375,700 |  |  |
Greysbridge Holdings Ltd | Kelso And Company |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage ownership |  |  |  |  | 30.00%
Greysbridge Holdings Ltd | Warburg Pincus LLC |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage ownership |  |  |  |  | 30.00%
Somers Holdings Ltd. |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Gain (loss) on deconsolidation |  | $ (33,100) |  |  |

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