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Segment Information (Reconciliation of Segment Results to Income from Continuing Operations, before Federal Income Tax) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total investment revenues | $ 385,098 | $ 173,347 | $ 344,188
Interest expense | (28,799) | (28,847) | (29,165)
Corporate expenses | (30,686) | (31,116) | (28,305)
Income before federal income tax | 458,412 | 280,186 | 505,310
Preferred stock dividends | (9,200) | (9,200) | (9,353)
Income available to common stockholders, before federal income tax | 449,212 | 270,986 | 495,957
Standard Commercial Lines [Member] |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Underwriting income (loss), before federal income tax | 157,306 | 143,696 | 198,596
Standard Personal Lines |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Underwriting income (loss), before federal income tax | (79,263) | (7,193) | 3,966
E&S Lines [Member] |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Underwriting income (loss), before federal income tax | 54,756 | 30,299 | 16,030
Operating Segments [Member] |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Total all segments | $ 517,897 | $ 340,149 | $ 562,780

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