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, 2023	Dec. 31, 2022
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 384,392	$ 285,391
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	6,655	10,219
Available-for-sale Securities, 12 Months or Greater, Fair Value	614,623	453,520
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	51,014	58,939
Available-for-sale Securities, Fair Value	999,015	738,911
Available For Sale Securities, Gross Unrealized Losses	57,669	69,158
State and municipal
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	264,273	1,720,443
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	3,013	89,272
Available-for-sale Securities, 12 Months or Greater, Fair Value	1,680,034	598,797
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	119,449	79,320
Available-for-sale Securities, Fair Value	1,944,307	2,319,240
Available For Sale Securities, Gross Unrealized Losses	122,462	168,592
Mortgage- Backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	278,819	1,099,549
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	2,025	75,430
Available-for-sale Securities, 12 Months or Greater, Fair Value	1,360,748	473,318
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	175,131	115,528
Available-for-sale Securities, Fair Value	1,639,567	1,572,867
Available For Sale Securities, Gross Unrealized Losses	177,156	190,958
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	413,511	1,569,647
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	2,070	48,390
Available-for-sale Securities, 12 Months or Greater, Fair Value	2,176,035	2,176,638
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	71,136	103,932
Available-for-sale Securities, Fair Value	2,589,546	3,746,285
Available For Sale Securities, Gross Unrealized Losses	73,206	152,322
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	874,754	3,690,856
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	11,975	150,115
Available-for-sale Securities, 12 Months or Greater, Fair Value	4,418,309	2,349,281
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	231,288	256,631
Available-for-sale Securities, Fair Value	5,293,063	6,040,137
Available For Sale Securities, Gross Unrealized Losses	243,263	406,746
Foreign government
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	204,908	477,672
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	1,758	29,815
Available-for-sale Securities, 12 Months or Greater, Fair Value	794,174	711,786
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	135,661	105,243
Available-for-sale Securities, Fair Value	999,082	1,189,458
Available For Sale Securities, Gross Unrealized Losses	137,419	135,058
Debt Securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Less Than 12 Months, Fair Value	2,420,657	8,843,558
Available-for-sale Securities, Less Than 12 Months, Gross Unrealized Losses	27,496	403,241
Available-for-sale Securities, 12 Months or Greater, Fair Value	11,043,923	6,763,340
Available-for-sale Securities, 12 Months or Greater, Gross Unrealized Losses	783,679	719,593
Available-for-sale Securities, Fair Value	13,464,580	15,606,898
Available For Sale Securities, Gross Unrealized Losses	$ 811,175	$ 1,122,834