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Segment Information (Income From Continuing Operations, Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Net investment income | $ 57,594 | $ 55,826 | $ 58,505 | $ 50,618 | $ 54,109 | $ 52,443 | $ 45,553 | $ 43,231 | $ 222,543 | $ 195,336 | $ 161,882
Total net realized and unrealized gains (losses) | $ (873) | $ (2,183) | $ 4,027 | $ 13,451 | $ (37,935) | $ (4,787) | $ (1,652) | $ (10,549) | 14,422 | (54,923) | 6,359
Total investment revenues |  |  |  |  |  |  |  |  | 236,965 | 140,413 | 168,241
Tax on investment income |  |  |  |  |  |  |  |  | 45,301 | 19,560 | 45,588
Total investment income, after federal income tax |  |  |  |  |  |  |  |  | 191,664 | 120,853 | 122,653
Standard Commercial Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | 145,990 | 109,104 | 149,514
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ 115,332 | $ 86,192 | $ 97,184
Combined Ratio |  |  |  |  |  |  |  |  | 92.90% | 94.30% | 91.60%
Return on Equity |  |  |  |  |  |  |  |  | 5.80% | 4.90% | 6.10%
Standard Personal Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | $ 8,260 | $ 12,764 | $ 11,104
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ 6,525 | $ 10,084 | $ 7,217
Combined Ratio |  |  |  |  |  |  |  |  | 97.30% | 95.80% | 96.20%
Return on Equity |  |  |  |  |  |  |  |  | 0.30% | 0.60% | 0.40%
E&S Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | $ 9,743 | $ (695) | $ (6,282)
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ 7,697 | $ (549) | $ (4,083)
Combined Ratio |  |  |  |  |  |  |  |  | 95.90% | 100.30% | 103.00%
Return on Equity |  |  |  |  |  |  |  |  | 0.40% | 0.00% | (0.30%)
Investments [Member] |  |  |  |  |  |  |  |  |  |  |
Return on Equity |  |  |  |  |  |  |  |  | 9.60% | 6.90% | 7.50%

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