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Investments - Securities in an Unrealized Loss Position Segregated by Type and Length of Time in an Unrealized Loss Position (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Fair value |  |
Less than 12 months | $ 382,062 | $ 909,943
12 months and greater | 1,534,269 | 1,633,651
Total Fair Value | 1,916,331 | 2,543,594
Amortized Cost |  |
Amortized cost, less than 12 months | 384,386 | 932,763
12 months and greater | 1,682,313 | 1,835,442
Total Cost or Amortized Cost | 2,066,699 | 2,768,205
Unrealized Loss |  |
Less than 12 months | (2,324) | (22,820)
12 months and greater | (148,044) | (201,791)
Total Unrealized Loss | (150,368) | (224,611)
U.S. government |  |
Fair value |  |
Less than 12 months | 11,055 | 303,226
12 months and greater | 105,375 | 157,418
Total Fair Value | 116,430 | 460,644
Amortized Cost |  |
Amortized cost, less than 12 months | 11,078 | 309,836
12 months and greater | 106,675 | 161,090
Total Cost or Amortized Cost | 117,753 | 470,926
Unrealized Loss |  |
Less than 12 months | (23) | (6,610)
12 months and greater | (1,300) | (3,672)
Total Unrealized Loss | (1,323) | (10,282)
U.S. Agency |  |
Fair value |  |
Less than 12 months |  | 24,024
12 months and greater | 30,621 | 18,330
Total Fair Value | 30,621 | 42,354
Amortized Cost |  |
Amortized cost, less than 12 months |  | 24,910
12 months and greater | 31,256 | 19,288
Total Cost or Amortized Cost | 31,256 | 44,198
Unrealized Loss |  |
Less than 12 months |  | (886)
12 months and greater | (635) | (958)
Total Unrealized Loss | (635) | (1,844)
Non-U.S. government & agency |  |
Fair value |  |
Less than 12 months |  | 4,075
12 months and greater | 4,188 | 3,796
Total Fair Value | 4,188 | 7,871
Amortized Cost |  |
Amortized cost, less than 12 months |  | 4,158
12 months and greater | 4,802 | 4,801
Total Cost or Amortized Cost | 4,802 | 8,959
Unrealized Loss |  |
Less than 12 months |  | (83)
12 months and greater | (614) | (1,005)
Total Unrealized Loss | (614) | (1,088)
Agency MBS |  |
Fair value |  |
Less than 12 months | 149,151 | 108,772
12 months and greater | 273,022 | 233,625
Total Fair Value | 422,173 | 342,397
Amortized Cost |  |
Amortized cost, less than 12 months | 149,737 | 111,674
12 months and greater | 303,901 | 273,972
Total Cost or Amortized Cost | 453,638 | 385,646
Unrealized Loss |  |
Less than 12 months | (586) | (2,902)
12 months and greater | (30,879) | (40,347)
Total Unrealized Loss | (31,465) | (43,249)
ABS/CMBS/MBS |  |
Fair value |  |
Less than 12 months | 72,227 | 43,027
12 months and greater | 149,479 | 164,433
Total Fair Value | 221,706 | 207,460
Amortized Cost |  |
Amortized cost, less than 12 months | 72,333 | 43,395
12 months and greater | 166,162 | 186,990
Total Cost or Amortized Cost | 238,495 | 230,385
Unrealized Loss |  |
Less than 12 months | (106) | (368)
12 months and greater | (16,683) | (22,557)
Total Unrealized Loss | (16,789) | (22,925)
Corporate |  |
Fair value |  |
Less than 12 months | 141,450 | 378,305
12 months and greater | 622,539 | 700,574
Total Fair Value | 763,989 | 1,078,879
Amortized Cost |  |
Amortized cost, less than 12 months | 142,776 | 389,299
12 months and greater | 649,774 | 745,283
Total Cost or Amortized Cost | 792,550 | 1,134,582
Unrealized Loss |  |
Less than 12 months | (1,326) | (10,994)
12 months and greater | (27,235) | (44,709)
Total Unrealized Loss | (28,561) | (55,703)
Municipal |  |
Fair value |  |
Less than 12 months | 8,179 | 48,514
12 months and greater | 349,045 | 355,475
Total Fair Value | 357,224 | 403,989
Amortized Cost |  |
Amortized cost, less than 12 months | 8,462 | 49,491
12 months and greater | 419,743 | 444,018
Total Cost or Amortized Cost | 428,205 | 493,509
Unrealized Loss |  |
Less than 12 months | (283) | (977)
12 months and greater | (70,698) | (88,543)
Total Unrealized Loss | $ (70,981) | $ (89,520)

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