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Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | $ 5,122,368 | $ 1,467,268
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (109,879) | (10,821)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 7,448,033 | 8,515,061
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (633,124) | (650,461)
Available-for-sale fixed maturity securities, estimated fair value | 12,570,401 | 9,982,329
Available-for-sale fixed maturity securities, gross unrealized holding losses | (743,003) | (661,282)
Short-term investments, available-for-sale, continuous unrealized loss position, less than 12 months | 163,503 | 52,601
Short-term investments, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss | (6,579) | (393)
Short-term investments, available-for-sale, continuous unrealized loss position, 12 months or longer | 0 | 0
Short-term investments, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss | 0 | 0
Short-term investments, available-for-sale, unrealized loss position, total | 163,503 | 52,601
Short-term investments, available-for-sale, unrealized loss position, accumulated loss | (6,579) | (393)
U.S. Treasury securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 1,593,711 | 317,027
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (27,213) | (2,147)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 1,444,869 | 1,507,784
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (41,256) | (60,257)
Available-for-sale fixed maturity securities, estimated fair value | 3,038,580 | 1,824,811
Available-for-sale fixed maturity securities, gross unrealized holding losses | (68,469) | (62,404)
U.S. government-sponsored enterprises [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 415,333 | 145,143
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (10,938) | (2,134)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 691,781 | 723,537
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (90,973) | (87,770)
Available-for-sale fixed maturity securities, estimated fair value | 1,107,114 | 868,680
Available-for-sale fixed maturity securities, gross unrealized holding losses | (101,911) | (89,904)
Obligations of states, municipalities and political subdivisions [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 1,133,275 | 679,124
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (21,242) | (3,881)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 2,024,298 | 2,332,281
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (178,278) | (177,697)
Available-for-sale fixed maturity securities, estimated fair value | 3,157,573 | 3,011,405
Available-for-sale fixed maturity securities, gross unrealized holding losses | (199,520) | (181,578)
Foreign governments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 1,056,877 | 83,396
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (29,890) | (394)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 1,246,215 | 1,492,912
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (177,412) | (141,614)
Available-for-sale fixed maturity securities, estimated fair value | 2,303,092 | 1,576,308
Available-for-sale fixed maturity securities, gross unrealized holding losses | (207,302) | (142,008)
Agency mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 757,562 | 189,977
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (13,880) | (1,872)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 1,710,436 | 1,889,272
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (109,992) | (133,739)
Available-for-sale fixed maturity securities, estimated fair value | 2,467,998 | 2,079,249
Available-for-sale fixed maturity securities, gross unrealized holding losses | (123,872) | (135,611)
Non-agency mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 0 | 0
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | 0 | 0
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 118,030 | 333,070
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (4,343) | (22,603)
Available-for-sale fixed maturity securities, estimated fair value | 118,030 | 333,070
Available-for-sale fixed maturity securities, gross unrealized holding losses | (4,343) | (22,603)
Corporate bonds [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 2,107 | 0
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (137) | 0
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 212,404 | 236,205
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (30,870) | (26,781)
Available-for-sale fixed maturity securities, estimated fair value | 214,511 | 236,205
Available-for-sale fixed maturity securities, gross unrealized holding losses | (31,007) | (26,781)
Total fixed maturities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale fixed maturity securities, estimated fair value, less than 12 months | 4,958,865 | 1,414,667
Available-for-sale fixed maturity securities, gross unrealized holding, less than 12 months | (103,300) | (10,428)
Available-for-sale fixed maturity securities, estimated fair value, 12 months or longer | 7,448,033 | 8,515,061
Available-for-sale fixed maturity securities, gross unrealized holding losses, 12 months or longer | (633,124) | (650,461)
Available-for-sale fixed maturity securities, estimated fair value | 12,406,898 | 9,929,728
Available-for-sale fixed maturity securities, gross unrealized holding losses | $ (736,424) | $ (660,889)

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