Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 5,621,577	$ 8,843,558
Gross Unrealized Losses, Less than 12 Months	120,273	403,241
Fair Value, 12 Months or Greater	11,676,271	6,763,340
Gross Unrealized Losses, 12 Months or Greater	1,047,729	719,593
Fair Value, Total	17,297,848	15,606,898
Gross Unrealized Losses, Total	1,168,002	1,122,834
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	605,944	285,391
Gross Unrealized Losses, Less than 12 Months	17,390	10,219
Fair Value, 12 Months or Greater	592,215	453,520
Gross Unrealized Losses, 12 Months or Greater	64,377	58,939
Fair Value, Total	1,198,159	738,911
Gross Unrealized Losses, Total	81,767	69,158
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	645,642	1,720,443
Gross Unrealized Losses, Less than 12 Months	15,255	89,272
Fair Value, 12 Months or Greater	1,728,892	598,797
Gross Unrealized Losses, 12 Months or Greater	167,938	79,320
Fair Value, Total	2,374,534	2,319,240
Gross Unrealized Losses, Total	183,193	168,592
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	688,848	1,099,549
Gross Unrealized Losses, Less than 12 Months	17,058	75,430
Fair Value, 12 Months or Greater	1,296,384	473,318
Gross Unrealized Losses, 12 Months or Greater	217,712	115,528
Fair Value, Total	1,985,232	1,572,867
Gross Unrealized Losses, Total	234,770	190,958
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,025,656	1,569,647
Gross Unrealized Losses, Less than 12 Months	8,774	48,390
Fair Value, 12 Months or Greater	2,584,224	2,176,638
Gross Unrealized Losses, 12 Months or Greater	100,251	103,932
Fair Value, Total	3,609,880	3,746,285
Gross Unrealized Losses, Total	109,025	152,322
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	2,091,830	3,690,856
Gross Unrealized Losses, Less than 12 Months	46,758	150,115
Fair Value, 12 Months or Greater	4,695,101	2,349,281
Gross Unrealized Losses, 12 Months or Greater	362,901	256,631
Fair Value, Total	6,786,931	6,040,137
Gross Unrealized Losses, Total	409,659	406,746
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	563,657	477,672
Gross Unrealized Losses, Less than 12 Months	15,038	29,815
Fair Value, 12 Months or Greater	779,455	711,786
Gross Unrealized Losses, 12 Months or Greater	134,550	105,243
Fair Value, Total	1,343,112	1,189,458
Gross Unrealized Losses, Total	$ 149,588	$ 135,058