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Segment Information (Reconciliation of Segment Results to Income Before Federal Income Tax (Details)) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
Investment income | $ 93,788 | $ 47,093 | $ 168,623 | $ 58,394
Interest expense | (7,366) | (7,928) | (14,725) | (15,529)
Corporate expenses | (9,112) | (6,345) | (18,666) | (15,405)
Income before federal income tax | 153,198 | 42,693 | 288,830 | 58,690
Preferred stock dividends | (2,300) | 0 | (4,753) | 0
Income available to common stockholders, before tax | 150,898 | 42,693 | 284,077 | 58,690
Standard Commercial Lines |  |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | $ 67,938 | $ 16,730 | $ 137,437 | $ 33,856
ROE Contribution | 8.20% | 2.40% | 8.30% | 2.40%
Standard Personal Lines |  |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | $ 5,644 | $ (6,325) | $ 13,339 | $ (5,938)
ROE Contribution | 0.70% | (0.90%) | 0.80% | (0.40%)
E&S Lines |  |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | $ 2,306 | $ (532) | $ 2,822 | $ 3,312
ROE Contribution | 0.30% | (0.10%) | 0.20% | 0.20%
Investments |  |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
ROE Contribution | 10.30% | 5.20% | 9.50% | 6.60%
Operating Segments |  |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |  |
Total income, before federal income tax all segments | $ 169,676 | $ 56,966 | $ 322,221 | $ 89,624

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