Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 3,946,235	$ 2,420,657
Gross Unrealized Losses, Less than 12 Months	40,721	27,496
Fair Value, 12 Months or Greater	10,214,690	11,043,923
Gross Unrealized Losses, 12 Months or Greater	820,320	783,679
Fair Value, Total	14,160,925	13,464,580
Gross Unrealized Losses, Total	861,041	811,175
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	439,699	384,392
Gross Unrealized Losses, Less than 12 Months	6,725	6,655
Fair Value, 12 Months or Greater	666,947	614,623
Gross Unrealized Losses, 12 Months or Greater	48,531	51,014
Fair Value, Total	1,106,646	999,015
Gross Unrealized Losses, Total	55,256	57,669
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	308,609	264,273
Gross Unrealized Losses, Less than 12 Months	3,376	3,013
Fair Value, 12 Months or Greater	1,764,296	1,680,034
Gross Unrealized Losses, 12 Months or Greater	120,513	119,449
Fair Value, Total	2,072,905	1,944,307
Gross Unrealized Losses, Total	123,889	122,462
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	288,696	278,819
Gross Unrealized Losses, Less than 12 Months	5,023	2,025
Fair Value, 12 Months or Greater	1,374,227	1,360,748
Gross Unrealized Losses, 12 Months or Greater	189,936	175,131
Fair Value, Total	1,662,923	1,639,567
Gross Unrealized Losses, Total	194,959	177,156
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,055,695	413,511
Gross Unrealized Losses, Less than 12 Months	3,765	2,070
Fair Value, 12 Months or Greater	1,282,145	2,176,035
Gross Unrealized Losses, 12 Months or Greater	60,820	71,136
Fair Value, Total	2,337,840	2,589,546
Gross Unrealized Losses, Total	64,585	73,206
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,532,300	874,754
Gross Unrealized Losses, Less than 12 Months	16,754	11,975
Fair Value, 12 Months or Greater	4,372,753	4,418,309
Gross Unrealized Losses, 12 Months or Greater	231,251	231,288
Fair Value, Total	5,905,053	5,293,063
Gross Unrealized Losses, Total	248,005	243,263
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	321,236	204,908
Gross Unrealized Losses, Less than 12 Months	5,078	1,758
Fair Value, 12 Months or Greater	754,322	794,174
Gross Unrealized Losses, 12 Months or Greater	169,269	135,661
Fair Value, Total	1,075,558	999,082
Gross Unrealized Losses, Total	$ 174,347	$ 137,419