v3.26.1
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
Mar. 31, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months $ 4,346,412 $ 946,645
Available-for-sale securities, gross unrealized holding losses, less than 12 months (36,292) (4,061)
Available-for-sale securities, estimated fair value, 12 months or longer 6,410,560 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (367,703) (327,375)
Available-for-sale securities, estimated fair value 10,756,972 7,763,106
Available-for-sale securities, gross unrealized holding losses (403,995) (331,436)
U.S. Treasury securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 1,109,592 197,135
Available-for-sale securities, gross unrealized holding losses, less than 12 months (5,438) (470)
Available-for-sale securities, estimated fair value, 12 months or longer 1,165,863 1,275,453
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (18,415) (13,171)
Available-for-sale securities, estimated fair value 2,275,455 1,472,588
Available-for-sale securities, gross unrealized holding losses (23,853) (13,641)
U.S. government-sponsored enterprises [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 181,210 108,490
Available-for-sale securities, gross unrealized holding losses, less than 12 months (1,027) (112)
Available-for-sale securities, estimated fair value, 12 months or longer 766,475 802,349
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (63,331) (57,631)
Available-for-sale securities, estimated fair value 947,685 910,839
Available-for-sale securities, gross unrealized holding losses (64,358) (57,743)
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 511,759 184,124
Available-for-sale securities, gross unrealized holding losses, less than 12 months (3,887) (970)
Available-for-sale securities, estimated fair value, 12 months or longer 1,762,168 1,871,154
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (107,636) (104,587)
Available-for-sale securities, estimated fair value 2,273,927 2,055,278
Available-for-sale securities, gross unrealized holding losses (111,523) (105,557)
Foreign governments, agencies and supranationals [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 798,190 214,787
Available-for-sale securities, gross unrealized holding losses, less than 12 months (17,276) (1,008)
Available-for-sale securities, estimated fair value, 12 months or longer 1,131,345 1,181,298
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (93,982) (72,686)
Available-for-sale securities, estimated fair value 1,929,535 1,396,085
Available-for-sale securities, gross unrealized holding losses (111,258) (73,694)
Agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 529,219 156,553
Available-for-sale securities, gross unrealized holding losses, less than 12 months (5,626) (701)
Available-for-sale securities, estimated fair value, 12 months or longer 1,359,971 1,446,048
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (61,356) (58,840)
Available-for-sale securities, estimated fair value 1,889,190 1,602,601
Available-for-sale securities, gross unrealized holding losses (66,982) (59,541)
Non-agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 5,857 5,889
Available-for-sale securities, gross unrealized holding losses, less than 12 months (42) (6)
Available-for-sale securities, estimated fair value, 12 months or longer 48,198 59,869
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (659) (532)
Available-for-sale securities, estimated fair value 54,055 65,758
Available-for-sale securities, gross unrealized holding losses (701) (538)
Corporate and university bonds [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 21,097 20,488
Available-for-sale securities, gross unrealized holding losses, less than 12 months (535) (174)
Available-for-sale securities, estimated fair value, 12 months or longer 176,540 180,290
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (22,324) (19,928)
Available-for-sale securities, estimated fair value 197,637 200,778
Available-for-sale securities, gross unrealized holding losses (22,859) (20,102)
Total fixed maturity securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 3,156,924 887,466
Available-for-sale securities, gross unrealized holding losses, less than 12 months (33,831) (3,441)
Available-for-sale securities, estimated fair value, 12 months or longer 6,410,560 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (367,703) (327,375)
Available-for-sale securities, estimated fair value 9,567,484 7,703,927
Available-for-sale securities, gross unrealized holding losses (401,534) (330,816)
Short-term investments [Member]    
Debt Securities, Available-for-sale [Line Items]    
Short-term investments, estimated fair value, less than 12 months 1,189,488 59,179
Short-term investments, gross unrealized holding losses, less than 12 months (2,461) (620)
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 1,189,488 59,179
Short-term investments, gross unrealized holding losses $ (2,461) $ (620)