Investments - Schedule of Unrealized Investment Losses by Class of Investment (Details) - USD ($)
$ in Thousands |
Mar. 31, 2026 |
Dec. 31, 2025 |
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
$ 3,225,281
|
$ 2,062,574
|
| Unrealized Loss, Less than Twelve Months |
(119,846)
|
(67,283)
|
| Fair Value, Twelve Months or Longer |
8,076,228
|
8,439,128
|
| Unrealized Loss, Twelve Months or Longer |
(1,726,699)
|
(1,570,524)
|
| Fair Value |
11,301,509
|
10,501,702
|
| Unrealized Loss |
(1,846,545)
|
(1,637,807)
|
| Investment grade securities: |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
3,154,838
|
2,015,800
|
| Unrealized Loss, Less than Twelve Months |
(113,343)
|
(60,556)
|
| Fair Value, Twelve Months or Longer |
7,822,071
|
8,156,383
|
| Unrealized Loss, Twelve Months or Longer |
(1,663,180)
|
(1,520,289)
|
| Fair Value |
10,976,909
|
10,172,183
|
| Unrealized Loss |
(1,776,523)
|
(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 |
12,947
|
4,894
|
| Unrealized Loss, Less than Twelve Months |
(185)
|
(454)
|
| Fair Value, Twelve Months or Longer |
366,139
|
368,750
|
| Unrealized Loss, Twelve Months or Longer |
(28,193)
|
(25,024)
|
| Fair Value |
379,086
|
373,644
|
| Unrealized Loss |
(28,378)
|
(25,478)
|
| Investment grade securities: | States, municipalities, and political subdivisions |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
420,682
|
535,186
|
| Unrealized Loss, Less than Twelve Months |
(9,520)
|
(12,491)
|
| Fair Value, Twelve Months or Longer |
1,647,106
|
1,731,104
|
| Unrealized Loss, Twelve Months or Longer |
(536,830)
|
(519,061)
|
| Fair Value |
2,067,788
|
2,266,290
|
| Unrealized Loss |
(546,350)
|
(531,552)
|
| Investment grade securities: | Foreign governments |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
11,087
|
5,616
|
| Unrealized Loss, Less than Twelve Months |
(227)
|
(26)
|
| Fair Value, Twelve Months or Longer |
24,784
|
25,370
|
| Unrealized Loss, Twelve Months or Longer |
(9,008)
|
(8,014)
|
| Fair Value |
35,871
|
30,986
|
| Unrealized Loss |
(9,235)
|
(8,040)
|
| Investment grade securities: | Corporates |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
2,681,753
|
1,451,887
|
| Unrealized Loss, Less than Twelve Months |
(103,229)
|
(47,523)
|
| Fair Value, Twelve Months or Longer |
5,782,731
|
6,029,780
|
| Unrealized Loss, Twelve Months or Longer |
(1,089,092)
|
(968,140)
|
| Fair Value |
8,464,484
|
7,481,667
|
| Unrealized Loss |
(1,192,321)
|
(1,015,663)
|
| Investment grade securities: | Corporates | Industrials |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
1,232,612
|
680,126
|
| Unrealized Loss, Less than Twelve Months |
(40,881)
|
(14,131)
|
| Fair Value, Twelve Months or Longer |
3,461,668
|
3,667,956
|
| Unrealized Loss, Twelve Months or Longer |
(660,477)
|
(591,006)
|
| Fair Value |
4,694,280
|
4,348,082
|
| Unrealized Loss |
(701,358)
|
(605,137)
|
| Investment grade securities: | Corporates | Financial |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
953,591
|
469,436
|
| Unrealized Loss, Less than Twelve Months |
(47,721)
|
(29,118)
|
| Fair Value, Twelve Months or Longer |
1,774,944
|
1,806,739
|
| Unrealized Loss, Twelve Months or Longer |
(335,824)
|
(294,440)
|
| Fair Value |
2,728,535
|
2,276,175
|
| Unrealized Loss |
(383,545)
|
(323,558)
|
| Investment grade securities: | Corporates | Utilities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
495,550
|
302,325
|
| Unrealized Loss, Less than Twelve Months |
(14,627)
|
(4,274)
|
| Fair Value, Twelve Months or Longer |
546,119
|
555,085
|
| Unrealized Loss, Twelve Months or Longer |
(92,791)
|
(82,694)
|
| Fair Value |
1,041,669
|
857,410
|
| Unrealized Loss |
(107,418)
|
(86,968)
|
| Investment grade securities: | Other asset-backed securities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
28,369
|
18,217
|
| Unrealized Loss, Less than Twelve Months |
(182)
|
(62)
|
| Fair Value, Twelve Months or Longer |
1,311
|
1,379
|
| Unrealized Loss, Twelve Months or Longer |
(57)
|
(50)
|
| Fair Value |
29,680
|
19,596
|
| Unrealized Loss |
(239)
|
(112)
|
| Below investment grade securities: |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
70,443
|
46,774
|
| Unrealized Loss, Less than Twelve Months |
(6,503)
|
(6,727)
|
| Fair Value, Twelve Months or Longer |
254,157
|
282,745
|
| Unrealized Loss, Twelve Months or Longer |
(63,519)
|
(50,235)
|
| Fair Value |
324,600
|
329,519
|
| Unrealized Loss |
(70,022)
|
(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 |
1,709
|
1,751
|
| Unrealized Loss, Twelve Months or Longer |
(251)
|
(210)
|
| Fair Value |
1,709
|
1,751
|
| Unrealized Loss |
(251)
|
(210)
|
| Below investment grade securities: | Corporates |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
56,870
|
46,774
|
| Unrealized Loss, Less than Twelve Months |
(6,475)
|
(6,727)
|
| Fair Value, Twelve Months or Longer |
252,448
|
280,994
|
| Unrealized Loss, Twelve Months or Longer |
(63,268)
|
(50,025)
|
| Fair Value |
309,318
|
327,768
|
| Unrealized Loss |
(69,743)
|
(56,752)
|
| Below investment grade securities: | Corporates | Industrials |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
31,189
|
35,564
|
| Unrealized Loss, Less than Twelve Months |
(6,090)
|
(6,631)
|
| Fair Value, Twelve Months or Longer |
129,820
|
141,446
|
| Unrealized Loss, Twelve Months or Longer |
(39,928)
|
(33,595)
|
| Fair Value |
161,009
|
177,010
|
| Unrealized Loss |
(46,018)
|
(40,226)
|
| Below investment grade securities: | Corporates | Financial |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
11,943
|
6,185
|
| Unrealized Loss, Less than Twelve Months |
(102)
|
(36)
|
| Fair Value, Twelve Months or Longer |
84,670
|
101,427
|
| Unrealized Loss, Twelve Months or Longer |
(17,118)
|
(10,372)
|
| Fair Value |
96,613
|
107,612
|
| Unrealized Loss |
(17,220)
|
(10,408)
|
| Below investment grade securities: | Corporates | Utilities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
13,738
|
5,025
|
| Unrealized Loss, Less than Twelve Months |
(283)
|
(60)
|
| Fair Value, Twelve Months or Longer |
37,958
|
38,121
|
| Unrealized Loss, Twelve Months or Longer |
(6,222)
|
(6,058)
|
| Fair Value |
51,696
|
43,146
|
| Unrealized Loss |
(6,505)
|
(6,118)
|
| Below investment grade securities: | Other asset-backed securities |
|
|
| Debt Securities, Available-for-sale [Line Items] |
|
|
| Fair Value, Less than Twelve Months |
13,573
|
0
|
| Unrealized Loss, Less than Twelve Months |
(28)
|
0
|
| Fair Value, Twelve Months or Longer |
0
|
0
|
| Unrealized Loss, Twelve Months or Longer |
0
|
0
|
| Fair Value |
13,573
|
0
|
| Unrealized Loss |
$ (28)
|
$ 0
|