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Segment Information - Reconciliation of Segment Results to Income Before Federal Income Tax (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Investment income | $ 106,214 | $ 94,850
Interest expense | (7,181) | (7,166)
Corporate expenses | (15,498) | (12,108)
Income, before federal income tax | 102,566 | 114,759
Preferred stock dividends | (2,300) | (2,300)
Income available to common stockholders, before federal income tax | 100,266 | 112,459
Standard Commercial Lines |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Underwriting income (loss) | 10,381 | 38,921
Standard Personal Lines |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Underwriting income (loss) | (5,335) | (13,073)
E&S Lines |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Underwriting income (loss) | 13,985 | 13,335
Investments: |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Investment income | 106,214 | 94,850
Operating Segments |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |
Total all segments | $ 125,245 | $ 134,033

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