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Fixed Maturity Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - External Credit Rating, Investment Grade - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
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U.S. government and government agency |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | $ 767,515 | $ 384,392
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 9,637 | 6,655
Available-for-sale Securities, 12 Months or Greater, Fair Value | 560,260 | 614,623
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 33,226 | 51,014
Available-for-sale Securities, Fair Value | 1,327,775 | 999,015
Available For Sale Securities, Gross Unrealized Losses | 42,863 | 57,669
State and municipal |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 348,116 | 264,273
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 8,027 | 3,013
Available-for-sale Securities, 12 Months or Greater, Fair Value | 1,411,761 | 1,680,034
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 81,430 | 119,449
Available-for-sale Securities, Fair Value | 1,759,877 | 1,944,307
Available For Sale Securities, Gross Unrealized Losses | 89,457 | 122,462
Mortgage- Backed |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 1,541,464 | 278,819
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 21,326 | 2,025
Available-for-sale Securities, 12 Months or Greater, Fair Value | 1,060,823 | 1,360,748
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 171,734 | 175,131
Available-for-sale Securities, Fair Value | 2,602,287 | 1,639,567
Available For Sale Securities, Gross Unrealized Losses | 193,060 | 177,156
Asset-backed |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 411,763 | 413,511
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 4,613 | 2,070
Available-for-sale Securities, 12 Months or Greater, Fair Value | 626,237 | 2,176,035
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 36,899 | 71,136
Available-for-sale Securities, Fair Value | 1,038,000 | 2,589,546
Available For Sale Securities, Gross Unrealized Losses | 41,512 | 73,206
Corporate |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 1,791,970 | 874,754
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 21,346 | 11,975
Available-for-sale Securities, 12 Months or Greater, Fair Value | 2,951,377 | 4,418,309
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 135,117 | 231,288
Available-for-sale Securities, Fair Value | 4,743,347 | 5,293,063
Available For Sale Securities, Gross Unrealized Losses | 156,463 | 243,263
Foreign government |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 600,103 | 204,908
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 17,933 | 1,758
Available-for-sale Securities, 12 Months or Greater, Fair Value | 476,479 | 794,174
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 167,440 | 135,661
Available-for-sale Securities, Fair Value | 1,076,582 | 999,082
Available For Sale Securities, Gross Unrealized Losses | 185,373 | 137,419
Debt Securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale Securities, Less Than 12 Months, Fair Value | 5,460,931 | 2,420,657
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses | 82,882 | 27,496
Available-for-sale Securities, 12 Months or Greater, Fair Value | 7,086,937 | 11,043,923
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses | 625,846 | 783,679
Available-for-sale Securities, Fair Value | 12,547,868 | 13,464,580
Available For Sale Securities, Gross Unrealized Losses | $ 708,728 | $ 811,175

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