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Investments (Investments Held in a Loss Position) (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Fair value |  |
Fair Value | $ 2,942,293 | $ 2,934,215
Less than 12 months, Fair Value | 958,097 | 293,116
12 months or longer, Fair Value | 1,984,196 | 2,641,099
Unrealized Loss |  |
Unrealized Loss | 275,926 | 274,690
Less than 12 months, Unrealized Loss | 75,300 | 21,226
12 months or longer, Unrealized Loss | 200,626 | 253,464
U.S. Treasury obligations |  |
Fair value |  |
Fair Value | 226,103 | 213,634
Less than 12 months, Fair Value | 40,747 | 32,925
12 months or longer, Fair Value | 185,356 | 180,709
Unrealized Loss |  |
Unrealized Loss | 17,597 | 16,474
Less than 12 months, Unrealized Loss | 1,412 | 1,364
12 months or longer, Unrealized Loss | 16,185 | 15,110
U.S. Government-sponsored enterprise obligations |  |
Fair value |  |
Fair Value | 18,928 | 18,428
Less than 12 months, Fair Value | 10,631 | 4,128
12 months or longer, Fair Value | 8,297 | 14,300
Unrealized Loss |  |
Unrealized Loss | 1,030 | 1,030
Less than 12 months, Unrealized Loss | 486 | 242
12 months or longer, Unrealized Loss | 544 | 788
State and municipal bonds |  |
Fair value |  |
Fair Value | 389,539 | 378,313
Less than 12 months, Fair Value | 98,395 | 48,960
12 months or longer, Fair Value | 291,144 | 329,353
Unrealized Loss |  |
Unrealized Loss | 30,020 | 29,871
Less than 12 months, Unrealized Loss | 5,941 | 2,287
12 months or longer, Unrealized Loss | 24,079 | 27,584
Corporate debt |  |
Fair value |  |
Fair Value | 1,498,062 | 1,524,940
Less than 12 months, Fair Value | 459,157 | 84,221
12 months or longer, Fair Value | 1,038,905 | 1,440,719
Unrealized Loss |  |
Unrealized Loss | 136,791 | 136,759
Less than 12 months, Unrealized Loss | 38,451 | 5,054
12 months or longer, Unrealized Loss | 98,340 | 131,705
Residential mortgage-backed securities |  |
Fair value |  |
Fair Value | 335,297 | 313,082
Less than 12 months, Fair Value | 130,058 | 74,463
12 months or longer, Fair Value | 205,239 | 238,619
Unrealized Loss |  |
Unrealized Loss | 59,073 | 53,795
Less than 12 months, Unrealized Loss | 16,800 | 10,271
12 months or longer, Unrealized Loss | 42,273 | 43,524
Agency commercial mortgage-backed securities |  |
Fair value |  |
Fair Value | 7,950 | 7,955
Less than 12 months, Fair Value | 2,652 | 212
12 months or longer, Fair Value | 5,298 | 7,743
Unrealized Loss |  |
Unrealized Loss | 1,014 | 987
Less than 12 months, Unrealized Loss | 344 | 1
12 months or longer, Unrealized Loss | 670 | 986
Other commercial mortgage-backed securities |  |
Fair value |  |
Fair Value | 214,030 | 184,416
Less than 12 months, Fair Value | 90,586 | 18,092
12 months or longer, Fair Value | 123,444 | 166,324
Unrealized Loss |  |
Unrealized Loss | 19,948 | 20,904
Less than 12 months, Unrealized Loss | 8,120 | 1,140
12 months or longer, Unrealized Loss | 11,828 | 19,764
Other asset-backed securities |  |
Fair value |  |
Fair Value | 252,384 | 293,447
Less than 12 months, Fair Value | 125,871 | 30,115
12 months or longer, Fair Value | 126,513 | 263,332
Unrealized Loss |  |
Unrealized Loss | 10,453 | 14,870
Less than 12 months, Unrealized Loss | 3,746 | 867
12 months or longer, Unrealized Loss | $ 6,707 | $ 14,003

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