Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 5,444,113	$ 8,843,558
Gross Unrealized Losses, Less than 12 Months	129,539	403,241
Fair Value, 12 Months or Greater	10,536,805	6,763,340
Gross Unrealized Losses, 12 Months or Greater	899,714	719,593
Fair Value, Total	15,980,918	15,606,898
Gross Unrealized Losses, Total	1,029,253	1,122,834
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	450,681	285,391
Gross Unrealized Losses, Less than 12 Months	8,273	10,219
Fair Value, 12 Months or Greater	554,499	453,520
Gross Unrealized Losses, 12 Months or Greater	62,453	58,939
Fair Value, Total	1,005,180	738,911
Gross Unrealized Losses, Total	70,726	69,158
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	813,039	1,720,443
Gross Unrealized Losses, Less than 12 Months	14,144	89,272
Fair Value, 12 Months or Greater	1,397,956	598,797
Gross Unrealized Losses, 12 Months or Greater	130,851	79,320
Fair Value, Total	2,210,995	2,319,240
Gross Unrealized Losses, Total	144,995	168,592
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	616,445	1,099,549
Gross Unrealized Losses, Less than 12 Months	14,056	75,430
Fair Value, 12 Months or Greater	1,136,423	473,318
Gross Unrealized Losses, 12 Months or Greater	175,973	115,528
Fair Value, Total	1,752,868	1,572,867
Gross Unrealized Losses, Total	190,029	190,958
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	779,215	1,569,647
Gross Unrealized Losses, Less than 12 Months	7,721	48,390
Fair Value, 12 Months or Greater	2,627,475	2,176,638
Gross Unrealized Losses, 12 Months or Greater	108,315	103,932
Fair Value, Total	3,406,690	3,746,285
Gross Unrealized Losses, Total	116,036	152,322
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	2,378,238	3,690,856
Gross Unrealized Losses, Less than 12 Months	55,011	150,115
Fair Value, 12 Months or Greater	3,985,296	2,349,281
Gross Unrealized Losses, 12 Months or Greater	323,373	256,631
Fair Value, Total	6,363,534	6,040,137
Gross Unrealized Losses, Total	378,384	406,746
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	406,495	477,672
Gross Unrealized Losses, Less than 12 Months	30,334	29,815
Fair Value, 12 Months or Greater	835,156	711,786
Gross Unrealized Losses, 12 Months or Greater	98,749	105,243
Fair Value, Total	1,241,651	1,189,458
Gross Unrealized Losses, Total	$ 129,083	$ 135,058