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Investments in Fixed Maturity Securities (Investments in Fixed Maturity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Amortized Cost	$ 44,437	$ 53,415
Held-to-maturity, allowance for credit loss	(25)	(43)	$ (114)
Total held to maturity, Gross Unrealized Gains	1,561	3,239
Total held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	45,973	56,611
Carrying Value	44,412	53,372
Fixed maturity securities available for sale at cost	22,966,462	20,861,830
Cumulative effect adjustment resulting from changes in accounting principles	(646)	(36,708)	(37,352)
Total available for sale, Gross Unrealized Gains	96,365	110,989
Total available for sale, Gross Unrealized Losses	(708,728)	(811,175)
Total available for sale, Fair Value	22,353,453	20,124,936
Total available for sale, Carrying Value	22,353,453	20,124,936
Fixed maturity securities, amortized cost	23,010,899	20,915,245
Total investments in fixed maturity securities, Gross Unrealized Gains	97,926	114,228
Total investments in fixed maturity securities, Gross Unrealized Losses	(708,728)	(811,175)
Total investments in fixed maturity securities, Fair Value	22,399,426	20,181,547
Total investments in fixed maturity securities, carrying value	22,397,865	20,178,308
Fixed maturity securities, allowance for credit loss	(671)	(36,751)
State and municipal
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Amortized Cost	42,145	50,547
Held-to-maturity, allowance for credit loss	(25)	(43)
Total held to maturity, Gross Unrealized Gains	1,492	3,132
Total held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	43,612	53,636
Carrying Value	42,120	50,504
Fixed maturity securities available for sale at cost	2,376,541	2,742,922
Cumulative effect adjustment resulting from changes in accounting principles	0	(757)	0
Total available for sale, Gross Unrealized Gains	7,560	14,719
Total available for sale, Gross Unrealized Losses	(89,457)	(122,462)
Total available for sale, Fair Value	2,294,644	2,634,422
Total available for sale, Carrying Value	2,294,644	2,634,422
Residential mortgage-backed
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Amortized Cost	2,292	2,868
Held-to-maturity, allowance for credit loss	0	0
Total held to maturity, Gross Unrealized Gains	69	107
Total held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	2,361	2,975
Carrying Value	2,292	2,868
Fixed maturity securities available for sale at cost	3,411,796	1,773,206
Cumulative effect adjustment resulting from changes in accounting principles	(5)	0
Total available for sale, Gross Unrealized Gains	11,047	12,780
Total available for sale, Gross Unrealized Losses	(189,630)	(163,844)
Total available for sale, Fair Value	3,233,208	1,622,142
Total available for sale, Carrying Value	3,233,208	1,622,142
U.S. government and government agency
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	2,268,596	1,762,997
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	9,608	11,403
Total available for sale, Gross Unrealized Losses	(42,863)	(57,669)
Total available for sale, Fair Value	2,235,341	1,716,731
Total available for sale, Carrying Value	2,235,341	1,716,731
Special Revenue
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	1,581,778	1,682,550
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	3,521	5,651
Total available for sale, Gross Unrealized Losses	(67,591)	(82,006)
Total available for sale, Fair Value	1,517,708	1,606,195
Total available for sale, Carrying Value	1,517,708	1,606,195
Debt, State Government
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	272,936	394,429
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	1,439	3,550
Total available for sale, Gross Unrealized Losses	(8,981)	(16,405)
Total available for sale, Fair Value	265,394	381,574
Total available for sale, Carrying Value	265,394	381,574
Revenue Subject to Refund
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	85,340	103,029
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	599	1,634
Total available for sale, Gross Unrealized Losses	(347)	(185)
Total available for sale, Fair Value	85,592	104,478
Total available for sale, Carrying Value	85,592	104,478
Corporation
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	158,322	166,873
Cumulative effect adjustment resulting from changes in accounting principles	0	(757)
Total available for sale, Gross Unrealized Gains	1,079	696
Total available for sale, Gross Unrealized Losses	(5,827)	(11,973)
Total available for sale, Fair Value	153,574	154,839
Total available for sale, Carrying Value	153,574	154,839
Debt, Local Government
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	278,165	396,041
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	922	3,188
Total available for sale, Gross Unrealized Losses	(6,711)	(11,893)
Total available for sale, Fair Value	272,376	387,336
Total available for sale, Carrying Value	272,376	387,336
Commercial Mortgage Backed Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	534,936	657,157
Cumulative effect adjustment resulting from changes in accounting principles	(425)	(158)
Total available for sale, Gross Unrealized Gains	1,201	626
Total available for sale, Gross Unrealized Losses	(3,430)	(13,312)
Total available for sale, Fair Value	532,282	644,313
Total available for sale, Carrying Value	532,282	644,313
Mortgage- Backed
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	3,946,732	2,430,363
Cumulative effect adjustment resulting from changes in accounting principles	(430)	(158)	(18)
Total available for sale, Gross Unrealized Gains	12,248	13,406
Total available for sale, Gross Unrealized Losses	(193,060)	(177,156)
Total available for sale, Fair Value	3,765,490	2,266,455
Total available for sale, Carrying Value	3,765,490	2,266,455
Asset-backed Securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	3,910,363	4,252,883
Cumulative effect adjustment resulting from changes in accounting principles	0	(1,164)	0
Total available for sale, Gross Unrealized Gains	16,161	8,527
Total available for sale, Gross Unrealized Losses	(41,512)	(73,206)
Total available for sale, Fair Value	3,885,012	4,187,040
Total available for sale, Carrying Value	3,885,012	4,187,040
Industrial Property
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	3,746,501	3,679,219
Cumulative effect adjustment resulting from changes in accounting principles	0	(40)
Total available for sale, Gross Unrealized Gains	14,518	24,312
Total available for sale, Gross Unrealized Losses	(93,820)	(143,936)
Total available for sale, Fair Value	3,667,199	3,559,555
Total available for sale, Carrying Value	3,667,199	3,559,555
Debt Security, Corporate, US
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	3,339,718	2,838,220
Cumulative effect adjustment resulting from changes in accounting principles	0	(4,986)
Total available for sale, Gross Unrealized Gains	18,871	14,681
Total available for sale, Gross Unrealized Losses	(38,076)	(68,681)
Total available for sale, Fair Value	3,320,513	2,779,234
Total available for sale, Carrying Value	3,320,513	2,779,234
Public Utility, Bonds
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	795,839	701,865
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	2,970	6,471
Total available for sale, Gross Unrealized Losses	(20,115)	(23,412)
Total available for sale, Fair Value	778,694	684,924
Total available for sale, Carrying Value	778,694	684,924
Other Security Investments
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	653,194	635,975
Cumulative effect adjustment resulting from changes in accounting principles	0	0
Total available for sale, Gross Unrealized Gains	2,493	1,605
Total available for sale, Gross Unrealized Losses	(4,452)	(7,234)
Total available for sale, Fair Value	651,235	630,346
Total available for sale, Carrying Value	651,235	630,346
Corporate
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	8,535,252	7,855,279
Cumulative effect adjustment resulting from changes in accounting principles	0	(5,026)	(4,701)
Total available for sale, Gross Unrealized Gains	38,852	47,069
Total available for sale, Gross Unrealized Losses	(156,463)	(243,263)
Total available for sale, Fair Value	8,417,641	7,654,059
Total available for sale, Carrying Value	8,417,641	7,654,059
Foreign government
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Fixed maturity securities available for sale at cost	1,928,978	1,817,386
Cumulative effect adjustment resulting from changes in accounting principles	(216)	(29,603)	$ (32,633)
Total available for sale, Gross Unrealized Gains	11,936	15,865
Total available for sale, Gross Unrealized Losses	(185,373)	(137,419)
Total available for sale, Fair Value	1,755,325	1,666,229
Total available for sale, Carrying Value	$ 1,755,325	$ 1,666,229

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