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Segment Information (Income Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Segment Reporting Information [Line Items] |  |  |  |
Net investment income | $ 93,032 | $ 68,185 | $ 246,479 | $ 158,596
Net realized and unrealized investment gains (losses) | 177 | 7,721 | 15,353 | (24,296)
Total investment segment income, before federal income tax | 93,209 | 75,906 | 261,832 | 134,300
Tax on investment income | 18,379 | 14,676 | 51,229 | 24,338
Total investment segment income, after federal income tax | 74,830 | 61,230 | 210,603 | 109,962
Standard Commercial Lines |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | 17,413 | 42,718 | 154,850 | 76,574
Underwriting gain (loss), after federal income tax | $ 13,756 | $ 33,746 | $ 122,332 | $ 60,493
Combined ratio | 97.20% | 92.30% | 91.40% | 95.10%
ROE Contribution | 2.10% | 5.70% | 6.20% | 3.50%
Standard Personal Lines |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | $ (11,146) | $ (14,404) | $ 2,193 | $ (20,342)
Underwriting gain (loss), after federal income tax | $ (8,805) | $ (11,379) | $ 1,732 | $ (16,070)
Combined ratio | 115.20% | 119.00% | 99.00% | 109.10%
ROE Contribution | (1.30%) | (1.90%) | 0.10% | (0.90%)
E&S Lines |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Underwriting gain (loss), before federal income tax | $ 4,672 | $ (7,277) | $ 7,494 | $ (3,965)
Underwriting gain (loss), after federal income tax | $ 3,691 | $ (5,748) | $ 5,920 | $ (3,132)
Combined ratio | 93.70% | 112.00% | 96.30% | 102.20%
ROE Contribution | 0.50% | (1.00%) | 0.30% | (0.20%)
Investments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
ROE Contribution | 11.00% | 9.40% | 10.10% | 7.50%

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