v3.25.1
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, 2025
Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months $ 4,153,208 $ 5,122,368
Available-for-sale securities, gross unrealized holding losses, less than 12 months (32,678) (109,879)
Available-for-sale securities, estimated fair value, 12 months or longer 7,244,968 7,448,033
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (514,200) (633,124)
Available-for-sale securities, estimated fair value 11,398,176 12,570,401
Available-for-sale securities, gross unrealized holding losses (546,878) (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 683,847 1,593,711
Available-for-sale securities, gross unrealized holding losses, less than 12 months (4,986) (27,213)
Available-for-sale securities, estimated fair value, 12 months or longer 1,277,393 1,444,869
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (28,576) (41,256)
Available-for-sale securities, estimated fair value 1,961,240 3,038,580
Available-for-sale securities, gross unrealized holding losses (33,562) (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 243,333 415,333
Available-for-sale securities, gross unrealized holding losses, less than 12 months (3,966) (10,938)
Available-for-sale securities, estimated fair value, 12 months or longer 713,889 691,781
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (73,587) (90,973)
Available-for-sale securities, estimated fair value 957,222 1,107,114
Available-for-sale securities, gross unrealized holding losses (77,553) (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 598,623 1,133,275
Available-for-sale securities, gross unrealized holding losses, less than 12 months (6,410) (21,242)
Available-for-sale securities, estimated fair value, 12 months or longer 2,050,569 2,024,298
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (147,577) (178,278)
Available-for-sale securities, estimated fair value 2,649,192 3,157,573
Available-for-sale securities, gross unrealized holding losses (153,987) (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 585,664 1,056,877
Available-for-sale securities, gross unrealized holding losses, less than 12 months (11,664) (29,890)
Available-for-sale securities, estimated fair value, 12 months or longer 1,268,147 1,246,215
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (149,136) (177,412)
Available-for-sale securities, estimated fair value 1,853,811 2,303,092
Available-for-sale securities, gross unrealized holding losses (160,800) (207,302)
Agency mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, estimated fair value, less than 12 months 162,695 757,562
Available-for-sale securities, gross unrealized holding losses, less than 12 months (3,264) (13,880)
Available-for-sale securities, estimated fair value, 12 months or longer 1,631,014 1,710,436
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (87,733) (109,992)
Available-for-sale securities, estimated fair value 1,793,709 2,467,998
Available-for-sale securities, gross unrealized holding losses (90,997) (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 101,954 118,030
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (2,783) (4,343)
Available-for-sale securities, estimated fair value 101,954 118,030
Available-for-sale securities, gross unrealized holding losses (2,783) (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 202,002 212,404
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (24,808) (30,870)
Available-for-sale securities, estimated fair value 202,002 214,511
Available-for-sale securities, gross unrealized holding losses (24,808) (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 2,274,162 4,958,865
Available-for-sale securities, gross unrealized holding losses, less than 12 months (30,290) (103,300)
Available-for-sale securities, estimated fair value, 12 months or longer 7,244,968 7,448,033
Available-for-sale securities, gross unrealized holding losses, 12 months or longer (514,200) (633,124)
Available-for-sale securities, estimated fair value 9,519,130 12,406,898
Available-for-sale securities, gross unrealized holding losses (544,490) (736,424)
Short-term investments [Member]    
Debt Securities, Available-for-sale [Line Items]    
Short-term investments, estimated fair value, less than 12 months 1,879,046 163,503
Short-term investments, gross unrealized holding losses, less than 12 months (2,388) (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 1,879,046 163,503
Short-term investments, gross unrealized holding losses $ (2,388) $ (6,579)