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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 | Jun. 30, 2025 | Dec. 31, 2024
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | $ 2,784,063 | $ 5,122,368
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (15,705) | (109,879)
Available-for-sale securities, estimated fair value, 12 months or longer | 6,940,018 | 7,448,033
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (390,598) | (633,124)
Available-for-sale securities, estimated fair value | 9,724,081 | 12,570,401
Available-for-sale securities, gross unrealized holding losses | (406,303) | (743,003)
U.S. Treasury securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 533,367 | 1,593,711
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (2,494) | (27,213)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,301,162 | 1,444,869
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (21,959) | (41,256)
Available-for-sale securities, estimated fair value | 1,834,529 | 3,038,580
Available-for-sale securities, gross unrealized holding losses | (24,453) | (68,469)
U.S. government-sponsored enterprises [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 233,480 | 415,333
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (3,935) | (10,938)
Available-for-sale securities, estimated fair value, 12 months or longer | 717,259 | 691,781
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (64,768) | (90,973)
Available-for-sale securities, estimated fair value | 950,739 | 1,107,114
Available-for-sale securities, gross unrealized holding losses | (68,703) | (101,911)
Obligations of states, municipalities and political subdivisions [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 494,098 | 1,133,275
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (5,135) | (21,242)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,994,681 | 2,024,298
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (131,149) | (178,278)
Available-for-sale securities, estimated fair value | 2,488,779 | 3,157,573
Available-for-sale securities, gross unrealized holding losses | (136,284) | (199,520)
Foreign governments, agencies and supranationals [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 137,638 | 1,056,877
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (1,344) | (29,890)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,176,691 | 1,246,215
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (72,442) | (177,412)
Available-for-sale securities, estimated fair value | 1,314,329 | 2,303,092
Available-for-sale securities, gross unrealized holding losses | (73,786) | (207,302)
Agency mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 218,371 | 757,562
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (2,544) | (13,880)
Available-for-sale securities, estimated fair value, 12 months or longer | 1,493,447 | 1,710,436
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (76,614) | (109,992)
Available-for-sale securities, estimated fair value | 1,711,818 | 2,467,998
Available-for-sale securities, gross unrealized holding losses | (79,158) | (123,872)
Non-agency mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 0 | 0
Available-for-sale securities, gross unrealized holding losses, less than 12 months | 0 | 0
Available-for-sale securities, estimated fair value, 12 months or longer | 70,357 | 118,030
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (1,264) | (4,343)
Available-for-sale securities, estimated fair value | 70,357 | 118,030
Available-for-sale securities, gross unrealized holding losses | (1,264) | (4,343)
Corporate and university bonds [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 0 | 2,107
Available-for-sale securities, gross unrealized holding losses, less than 12 months | 0 | (137)
Available-for-sale securities, estimated fair value, 12 months or longer | 186,421 | 212,404
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (22,402) | (30,870)
Available-for-sale securities, estimated fair value | 186,421 | 214,511
Available-for-sale securities, gross unrealized holding losses | (22,402) | (31,007)
Total fixed maturity securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 1,616,954 | 4,958,865
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (15,452) | (103,300)
Available-for-sale securities, estimated fair value, 12 months or longer | 6,940,018 | 7,448,033
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (390,598) | (633,124)
Available-for-sale securities, estimated fair value | 8,556,972 | 12,406,898
Available-for-sale securities, gross unrealized holding losses | (406,050) | (736,424)
Short-term investments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Short-term investments, estimated fair value, less than 12 months | 1,167,109 | 163,503
Short-term investments, gross unrealized holding losses, less than 12 months | (253) | (6,579)
Short-term investments, estimated fair value, 12 months or longer | 0 | 0
Short-term investments, gross unrealized holding losses, 12 months or longer | 0 | 0
Short-term investments, estimated fair value | 1,167,109 | 163,503
Short-term investments, gross unrealized holding losses | $ (253) | $ (6,579)

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