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Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Net realized gains and losses: |  |  |  |
Available for sale securities, gross gains on investment sales |  | $ 81,161 | $ 313,886 | $ 595,941
Available for sale securities, gross losses on investment sales |  | (317,150) | (156,791) | (117,282)
Equity securities at fair value, net realized gains (losses) on sales during the period |  | 74,922 | 122,606 | 26,849
Equity securities at fair value, net unrealized gains (losses) on equity securities still held at reporting date |  | (267,927) | 48,746 | 102,394
Allowance for credit losses - investment related |  | (43,909) | (2,100) | (3,597)
Allowance for credit losses - underwriting related |  | (13,274) | 1,062 | (10,007)
Derivative instruments |  | (75,023) | (32,390) | 179,675
Other | [1] | (3,553) | (53,537) | 3,575
Net realized gains (losses) |  | $ (662,734) | 379,845 | 823,460
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] |  | Net realized gains (losses) |  |
Somers Holdings Ltd. |  |  |  |
Net realized gains and losses: |  |  |  |
Gain (loss) on deconsolidation |  |  | (33,100) |
Fixed maturities |  |  |  |
Net realized gains and losses: |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | $ (70,951) | 7,953 | 15,881
Other investments |  |  |  |
Net realized gains and losses: |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | (19,498) | 116,781 | 13,656
Equity securities |  |  |  |
Net realized gains and losses: |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | (4,520) | 13,028 | 14,629
Short-term investments |  |  |  |
Net realized gains and losses: |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | $ (3,012) | $ 601 | $ 2,279
[1] | 2021 period reflected $33.1 million of losses related to the Company’sdeconsolidation of Somers

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