Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	$ 1,421,474	$ 2,420,657
Gross Unrealized Losses, Less than 12 Months	30,142	27,496
Fair Value, 12 Months or Greater	8,116,556	11,043,923
Gross Unrealized Losses, 12 Months or Greater	557,767	783,679
Fair Value, Total	9,538,030	13,464,580
Gross Unrealized Losses, Total	587,909	811,175
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	142,850	384,392
Gross Unrealized Losses, Less than 12 Months	3,128	6,655
Fair Value, 12 Months or Greater	586,823	614,623
Gross Unrealized Losses, 12 Months or Greater	32,946	51,014
Fair Value, Total	729,673	999,015
Gross Unrealized Losses, Total	36,074	57,669
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	119,658	264,273
Gross Unrealized Losses, Less than 12 Months	2,875	3,013
Fair Value, 12 Months or Greater	1,636,735	1,680,034
Gross Unrealized Losses, 12 Months or Greater	67,333	119,449
Fair Value, Total	1,756,393	1,944,307
Gross Unrealized Losses, Total	70,208	122,462
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	237,206	278,819
Gross Unrealized Losses, Less than 12 Months	925	2,025
Fair Value, 12 Months or Greater	1,162,601	1,360,748
Gross Unrealized Losses, 12 Months or Greater	132,922	175,131
Fair Value, Total	1,399,807	1,639,567
Gross Unrealized Losses, Total	133,847	177,156
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	471,907	413,511
Gross Unrealized Losses, Less than 12 Months	1,236	2,070
Fair Value, 12 Months or Greater	787,420	2,176,035
Gross Unrealized Losses, 12 Months or Greater	35,541	71,136
Fair Value, Total	1,259,327	2,589,546
Gross Unrealized Losses, Total	36,777	73,206
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	308,606	874,754
Gross Unrealized Losses, Less than 12 Months	4,573	11,975
Fair Value, 12 Months or Greater	3,325,568	4,418,309
Gross Unrealized Losses, 12 Months or Greater	126,794	231,288
Fair Value, Total	3,634,174	5,293,063
Gross Unrealized Losses, Total	131,367	243,263
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair value, Less than 12 months	141,247	204,908
Gross Unrealized Losses, Less than 12 Months	17,405	1,758
Fair Value, 12 Months or Greater	617,409	794,174
Gross Unrealized Losses, 12 Months or Greater	162,231	135,661
Fair Value, Total	758,656	999,082
Gross Unrealized Losses, Total	$ 179,636	$ 137,419