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
Jun. 30, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months $ 6,840,347 $ 946,645
Available-for-sale securities, gross unrealized holding losses, less than 12 months (66,368) (4,061)
Available-for-sale securities, estimated fair value, 12 months or longer 5,834,865 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (372,627) (327,375)
Available-for-sale securities, estimated fair value 12,675,212 7,763,106
Available-for-sale securities, gross unrealized holding losses (438,995) (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 2,250,496 197,135
Available-for-sale securities, gross unrealized holding losses, less than 12 months (19,252) (470)
Available-for-sale securities, estimated fair value, 12 months or longer 1,010,529 1,275,453
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (22,555) (13,171)
Available-for-sale securities, estimated fair value 3,261,025 1,472,588
Available-for-sale securities, gross unrealized holding losses (41,807) (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 357,578 108,490
Available-for-sale securities, gross unrealized holding losses, less than 12 months (2,998) (112)
Available-for-sale securities, estimated fair value, 12 months or longer 749,419 802,349
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (66,831) (57,631)
Available-for-sale securities, estimated fair value 1,106,997 910,839
Available-for-sale securities, gross unrealized holding losses (69,829) (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 774,473 184,124
Available-for-sale securities, gross unrealized holding losses, less than 12 months (8,720) (970)
Available-for-sale securities, estimated fair value, 12 months or longer 1,581,088 1,871,154
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (112,652) (104,587)
Available-for-sale securities, estimated fair value 2,355,561 2,055,278
Available-for-sale securities, gross unrealized holding losses (121,372) (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 1,095,865 214,787
Available-for-sale securities, gross unrealized holding losses, less than 12 months (17,396) (1,008)
Available-for-sale securities, estimated fair value, 12 months or longer 995,623 1,181,298
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (84,196) (72,686)
Available-for-sale securities, estimated fair value 2,091,488 1,396,085
Available-for-sale securities, gross unrealized holding losses (101,592) (73,694)
Agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 821,781 156,553
Available-for-sale securities, gross unrealized holding losses, less than 12 months (12,529) (701)
Available-for-sale securities, estimated fair value, 12 months or longer 1,282,216 1,446,048
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (63,875) (58,840)
Available-for-sale securities, estimated fair value 2,103,997 1,602,601
Available-for-sale securities, gross unrealized holding losses (76,404) (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 5,847 5,889
Available-for-sale securities, gross unrealized holding losses, less than 12 months (55) (6)
Available-for-sale securities, estimated fair value, 12 months or longer 41,148 59,869
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (655) (532)
Available-for-sale securities, estimated fair value 46,995 65,758
Available-for-sale securities, gross unrealized holding losses (710) (538)
Corporate and university bonds [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 20,971 20,488
Available-for-sale securities, gross unrealized holding losses, less than 12 months (392) (174)
Available-for-sale securities, estimated fair value, 12 months or longer 174,842 180,290
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (21,863) (19,928)
Available-for-sale securities, estimated fair value 195,813 200,778
Available-for-sale securities, gross unrealized holding losses (22,255) (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 5,327,011 887,466
Available-for-sale securities, gross unrealized holding losses, less than 12 months (61,342) (3,441)
Available-for-sale securities, estimated fair value, 12 months or longer 5,834,865 6,816,461
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (372,627) (327,375)
Available-for-sale securities, estimated fair value 11,161,876 7,703,927
Available-for-sale securities, gross unrealized holding losses (433,969) (330,816)
Short-term investments [Member]    
Debt Securities, Available-for-sale [Line Items]    
Short-term investments, estimated fair value, less than 12 months 1,513,336 59,179
Short-term investments, gross unrealized holding losses, less than 12 months (5,026) (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 1,513,336 59,179
Short-term investments, gross unrealized holding losses $ (5,026) $ (620)