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Net Investment Income (Net Investment Income) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Net Investment Income [Line Items] |  |  |
Gross investment income | $ 1,059,751 | $ 789,106 | $ 679,414
Investment expense | (6,916) | (9,921) | (7,796)
Net investment income | 1,052,835 | 779,185 | 671,618
Fixed maturity securities, including cash and cash equivalents and loans receivable |  |  |
Net Investment Income [Line Items] |  |  |
Gross investment income | 929,098 | 549,281 | 382,001
Investment funds |  |  |
Net Investment Income [Line Items] |  |  |
Gross investment income | 16,743 | 145,099 | 220,014
Arbitrage trading account (1) |  |  |
Net Investment Income [Line Items] |  |  |
Gross investment income | 69,369 | 45,213 | 37,676
Real estate |  |  |
Net Investment Income [Line Items] |  |  |
Gross investment income | (11,185) | (3,087) | 7,703
Equity securities |  |  |
Net Investment Income [Line Items] |  |  |
Gross investment income | $ 55,726 | $ 52,600 | $ 32,020

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