v3.25.2
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
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)