Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 4,216,166	$ 5,460,931
Gross Unrealized Losses, Less than 12 Months	48,178	82,882
Fair Value, 12 Months or Greater	6,602,064	7,086,937
Gross Unrealized Losses, 12 Months or Greater	549,864	625,846
Fair Value, Total	10,818,230	12,547,868
Gross Unrealized Losses, Total	598,042	708,728
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	730,275	767,515
Gross Unrealized Losses, Less than 12 Months	5,910	9,637
Fair Value, 12 Months or Greater	576,231	560,260
Gross Unrealized Losses, 12 Months or Greater	22,185	33,226
Fair Value, Total	1,306,506	1,327,775
Gross Unrealized Losses, Total	28,095	42,863
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	238,597	348,116
Gross Unrealized Losses, Less than 12 Months	3,961	8,027
Fair Value, 12 Months or Greater	1,371,842	1,411,761
Gross Unrealized Losses, 12 Months or Greater	61,160	81,430
Fair Value, Total	1,610,439	1,759,877
Gross Unrealized Losses, Total	65,121	89,457
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	925,345	1,541,464
Gross Unrealized Losses, Less than 12 Months	10,699	21,326
Fair Value, 12 Months or Greater	987,497	1,060,823
Gross Unrealized Losses, 12 Months or Greater	149,560	171,734
Fair Value, Total	1,912,842	2,602,287
Gross Unrealized Losses, Total	160,259	193,060
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,110,183	411,763
Gross Unrealized Losses, Less than 12 Months	4,871	4,613
Fair Value, 12 Months or Greater	590,123	626,237
Gross Unrealized Losses, 12 Months or Greater	29,118	36,899
Fair Value, Total	1,700,306	1,038,000
Gross Unrealized Losses, Total	33,989	41,512
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	836,171	1,791,970
Gross Unrealized Losses, Less than 12 Months	8,431	21,346
Fair Value, 12 Months or Greater	2,646,520	2,951,377
Gross Unrealized Losses, 12 Months or Greater	107,914	135,117
Fair Value, Total	3,482,691	4,743,347
Gross Unrealized Losses, Total	116,345	156,463
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	375,595	600,103
Gross Unrealized Losses, Less than 12 Months	14,306	17,933
Fair Value, 12 Months or Greater	429,851	476,479
Gross Unrealized Losses, 12 Months or Greater	179,927	167,440
Fair Value, Total	805,446	1,076,582
Gross Unrealized Losses, Total	$ 194,233	$ 185,373