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Investments - Assets Measured at Fair Value (Details) - USD ($) $ in Thousands | Mar. 31, 2026 | Dec. 31, 2025
--- | --- | ---
Assets measured at Fair Value |  |
Available-for-sale fixed income | $ 3,528,692 | $ 3,533,336
Equity securities | 864,912 | 898,876
U.S. government |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 307,140 | 335,223
U.S. Agency |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 27,288 | 37,927
Non-U.S. government & agency |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 16,286 | 13,547
Agency MBS |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 600,802 | 610,675
ABS/CMBS/MBS |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 710,301 | 672,984
Corporate |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 1,504,405 | 1,491,506
Municipal |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 362,470 | 371,474
Fair Value Measured on Recurring Basis |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 3,528,692 | 3,533,336
Equity securities | 864,912 | 898,876
Total assets at fair value | 4,393,604 | 4,432,212
Fair Value Measured on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Assets measured at Fair Value |  |
Equity securities | 856,689 | 890,622
Total assets at fair value | 856,689 | 890,622
Fair Value Measured on Recurring Basis | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 3,404,934 | 3,423,029
Total assets at fair value | 3,404,934 | 3,423,029
Fair Value Measured on Recurring Basis | Significant Unobservable Inputs (Level 3) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 123,758 | 110,307
Equity securities | 8,223 | 8,254
Total assets at fair value | 131,981 | 118,561
Fair Value Measured on Recurring Basis | U.S. government |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 307,140 | 335,223
Fair Value Measured on Recurring Basis | U.S. government | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 307,140 | 335,223
Fair Value Measured on Recurring Basis | U.S. Agency |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 27,288 | 37,927
Fair Value Measured on Recurring Basis | U.S. Agency | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 27,288 | 37,927
Fair Value Measured on Recurring Basis | Non-U.S. government & agency |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 16,286 | 13,547
Fair Value Measured on Recurring Basis | Non-U.S. government & agency | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 14,191 | 11,417
Fair Value Measured on Recurring Basis | Non-U.S. government & agency | Significant Unobservable Inputs (Level 3) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 2,095 | 2,130
Fair Value Measured on Recurring Basis | Agency MBS |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 600,802 | 610,675
Fair Value Measured on Recurring Basis | Agency MBS | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 600,802 | 610,675
Fair Value Measured on Recurring Basis | ABS/CMBS/MBS |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 710,301 | 672,984
Fair Value Measured on Recurring Basis | ABS/CMBS/MBS | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 710,301 | 672,984
Fair Value Measured on Recurring Basis | Corporate |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 1,504,405 | 1,491,506
Fair Value Measured on Recurring Basis | Corporate | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 1,382,742 | 1,383,329
Fair Value Measured on Recurring Basis | Corporate | Significant Unobservable Inputs (Level 3) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 121,663 | 108,177
Fair Value Measured on Recurring Basis | Municipal |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | 362,470 | 371,474
Fair Value Measured on Recurring Basis | Municipal | Significant Other Observable Inputs (Level 2) |  |
Assets measured at Fair Value |  |
Available-for-sale fixed income | $ 362,470 | $ 371,474

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