Investments - Schedule of Unrealized Investment Losses by Class of Investment (Details) - USD ($)
$ in Thousands |
Jun. 30, 2026 |
Dec. 31, 2025 |
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
$ 2,886,787
|
$ 2,062,574
|
| Unrealized Loss, Less than Twelve Months |
(95,987)
|
(67,283)
|
| Fair Value, Twelve Months or Longer |
8,162,572
|
8,439,128
|
| Unrealized Loss, Twelve Months or Longer |
(1,579,114)
|
(1,570,524)
|
| Fair Value |
11,049,359
|
10,501,702
|
| Unrealized Loss |
(1,675,101)
|
(1,637,807)
|
| Investment grade securities: |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
2,792,200
|
2,015,800
|
| Unrealized Loss, Less than Twelve Months |
(90,355)
|
(60,556)
|
| Fair Value, Twelve Months or Longer |
7,905,981
|
8,156,383
|
| Unrealized Loss, Twelve Months or Longer |
(1,519,647)
|
(1,520,289)
|
| Fair Value |
10,698,181
|
10,172,183
|
| Unrealized Loss |
(1,610,002)
|
(1,580,845)
|
| Investment grade securities: | U.S. Government direct, guaranteed, and government-sponsored enterprises |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
22,492
|
4,894
|
| Unrealized Loss, Less than Twelve Months |
(290)
|
(454)
|
| Fair Value, Twelve Months or Longer |
361,770
|
368,750
|
| Unrealized Loss, Twelve Months or Longer |
(30,807)
|
(25,024)
|
| Fair Value |
384,262
|
373,644
|
| Unrealized Loss |
(31,097)
|
(25,478)
|
| Investment grade securities: | States, municipalities, and political subdivisions |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
577,998
|
535,186
|
| Unrealized Loss, Less than Twelve Months |
(13,249)
|
(12,491)
|
| Fair Value, Twelve Months or Longer |
1,729,875
|
1,731,104
|
| Unrealized Loss, Twelve Months or Longer |
(466,467)
|
(519,061)
|
| Fair Value |
2,307,873
|
2,266,290
|
| Unrealized Loss |
(479,716)
|
(531,552)
|
| Investment grade securities: | Foreign governments |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
0
|
5,616
|
| Unrealized Loss, Less than Twelve Months |
0
|
(26)
|
| Fair Value, Twelve Months or Longer |
24,893
|
25,370
|
| Unrealized Loss, Twelve Months or Longer |
(7,699)
|
(8,014)
|
| Fair Value |
24,893
|
30,986
|
| Unrealized Loss |
(7,699)
|
(8,040)
|
| Investment grade securities: | Corporates |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
2,176,916
|
1,451,887
|
| Unrealized Loss, Less than Twelve Months |
(76,709)
|
(47,523)
|
| Fair Value, Twelve Months or Longer |
5,788,196
|
6,029,780
|
| Unrealized Loss, Twelve Months or Longer |
(1,014,613)
|
(968,140)
|
| Fair Value |
7,965,112
|
7,481,667
|
| Unrealized Loss |
(1,091,322)
|
(1,015,663)
|
| Investment grade securities: | Corporates | Industrials |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
1,019,521
|
680,126
|
| Unrealized Loss, Less than Twelve Months |
(27,839)
|
(14,131)
|
| Fair Value, Twelve Months or Longer |
3,460,943
|
3,667,956
|
| Unrealized Loss, Twelve Months or Longer |
(614,025)
|
(591,006)
|
| Fair Value |
4,480,464
|
4,348,082
|
| Unrealized Loss |
(641,864)
|
(605,137)
|
| Investment grade securities: | Corporates | Financial |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
716,497
|
469,436
|
| Unrealized Loss, Less than Twelve Months |
(39,257)
|
(29,118)
|
| Fair Value, Twelve Months or Longer |
1,780,569
|
1,806,739
|
| Unrealized Loss, Twelve Months or Longer |
(313,186)
|
(294,440)
|
| Fair Value |
2,497,066
|
2,276,175
|
| Unrealized Loss |
(352,443)
|
(323,558)
|
| Investment grade securities: | Corporates | Utilities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
440,898
|
302,325
|
| Unrealized Loss, Less than Twelve Months |
(9,613)
|
(4,274)
|
| Fair Value, Twelve Months or Longer |
546,684
|
555,085
|
| Unrealized Loss, Twelve Months or Longer |
(87,402)
|
(82,694)
|
| Fair Value |
987,582
|
857,410
|
| Unrealized Loss |
(97,015)
|
(86,968)
|
| Investment grade securities: | Other asset-backed securities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
14,794
|
18,217
|
| Unrealized Loss, Less than Twelve Months |
(107)
|
(62)
|
| Fair Value, Twelve Months or Longer |
1,247
|
1,379
|
| Unrealized Loss, Twelve Months or Longer |
(61)
|
(50)
|
| Fair Value |
16,041
|
19,596
|
| Unrealized Loss |
(168)
|
(112)
|
| Below investment grade securities: |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
94,587
|
46,774
|
| Unrealized Loss, Less than Twelve Months |
(5,632)
|
(6,727)
|
| Fair Value, Twelve Months or Longer |
256,591
|
282,745
|
| Unrealized Loss, Twelve Months or Longer |
(59,467)
|
(50,235)
|
| Fair Value |
351,178
|
329,519
|
| Unrealized Loss |
(65,099)
|
(56,962)
|
| Below investment grade securities: | States, municipalities, and political subdivisions |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
0
|
0
|
| Unrealized Loss, Less than Twelve Months |
0
|
0
|
| Fair Value, Twelve Months or Longer |
1,796
|
1,751
|
| Unrealized Loss, Twelve Months or Longer |
(163)
|
(210)
|
| Fair Value |
1,796
|
1,751
|
| Unrealized Loss |
(163)
|
(210)
|
| Below investment grade securities: | Corporates |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
94,105
|
46,774
|
| Unrealized Loss, Less than Twelve Months |
(5,632)
|
(6,727)
|
| Fair Value, Twelve Months or Longer |
254,795
|
280,994
|
| Unrealized Loss, Twelve Months or Longer |
(59,304)
|
(50,025)
|
| Fair Value |
348,900
|
327,768
|
| Unrealized Loss |
(64,936)
|
(56,752)
|
| Below investment grade securities: | Corporates | Industrials |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
61,696
|
35,564
|
| Unrealized Loss, Less than Twelve Months |
(5,007)
|
(6,631)
|
| Fair Value, Twelve Months or Longer |
130,832
|
141,446
|
| Unrealized Loss, Twelve Months or Longer |
(38,127)
|
(33,595)
|
| Fair Value |
192,528
|
177,010
|
| Unrealized Loss |
(43,134)
|
(40,226)
|
| Below investment grade securities: | Corporates | Financial |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
18,636
|
6,185
|
| Unrealized Loss, Less than Twelve Months |
(377)
|
(36)
|
| Fair Value, Twelve Months or Longer |
87,111
|
101,427
|
| Unrealized Loss, Twelve Months or Longer |
(14,666)
|
(10,372)
|
| Fair Value |
105,747
|
107,612
|
| Unrealized Loss |
(15,043)
|
(10,408)
|
| Below investment grade securities: | Corporates | Utilities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
13,773
|
5,025
|
| Unrealized Loss, Less than Twelve Months |
(248)
|
(60)
|
| Fair Value, Twelve Months or Longer |
36,852
|
38,121
|
| Unrealized Loss, Twelve Months or Longer |
(6,511)
|
(6,058)
|
| Fair Value |
50,625
|
43,146
|
| Unrealized Loss |
(6,759)
|
(6,118)
|
| Below investment grade securities: | Other asset-backed securities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
482
|
0
|
| Unrealized Loss, Less than Twelve Months |
0
|
0
|
| Fair Value, Twelve Months or Longer |
0
|
0
|
| Unrealized Loss, Twelve Months or Longer |
0
|
0
|
| Fair Value |
482
|
0
|
| Unrealized Loss |
$ 0
|
$ 0
|