Fixed Maturity Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - External Credit Rating, Investment Grade - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 767,515	$ 384,392
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	9,637	6,655
Available-for-sale Securities, 12 Months or Greater, Fair Value	560,260	614,623
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	33,226	51,014
Available-for-sale Securities, Fair Value	1,327,775	999,015
Available For Sale Securities, Gross Unrealized Losses	42,863	57,669
State and municipal
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	348,116	264,273
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	8,027	3,013
Available-for-sale Securities, 12 Months or Greater, Fair Value	1,411,761	1,680,034
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	81,430	119,449
Available-for-sale Securities, Fair Value	1,759,877	1,944,307
Available For Sale Securities, Gross Unrealized Losses	89,457	122,462
Mortgage- Backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,541,464	278,819
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	21,326	2,025
Available-for-sale Securities, 12 Months or Greater, Fair Value	1,060,823	1,360,748
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	171,734	175,131
Available-for-sale Securities, Fair Value	2,602,287	1,639,567
Available For Sale Securities, Gross Unrealized Losses	193,060	177,156
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	411,763	413,511
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	4,613	2,070
Available-for-sale Securities, 12 Months or Greater, Fair Value	626,237	2,176,035
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	36,899	71,136
Available-for-sale Securities, Fair Value	1,038,000	2,589,546
Available For Sale Securities, Gross Unrealized Losses	41,512	73,206
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	1,791,970	874,754
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	21,346	11,975
Available-for-sale Securities, 12 Months or Greater, Fair Value	2,951,377	4,418,309
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	135,117	231,288
Available-for-sale Securities, Fair Value	4,743,347	5,293,063
Available For Sale Securities, Gross Unrealized Losses	156,463	243,263
Foreign government
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	600,103	204,908
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	17,933	1,758
Available-for-sale Securities, 12 Months or Greater, Fair Value	476,479	794,174
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	167,440	135,661
Available-for-sale Securities, Fair Value	1,076,582	999,082
Available For Sale Securities, Gross Unrealized Losses	185,373	137,419
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	5,460,931	2,420,657
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	82,882	27,496
Available-for-sale Securities, 12 Months or Greater, Fair Value	7,086,937	11,043,923
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	625,846	783,679
Available-for-sale Securities, Fair Value	12,547,868	13,464,580
Available For Sale Securities, Gross Unrealized Losses	$ 708,728	$ 811,175