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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, 2018 | [1] | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | [1] | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Net investment income | $ 54,109 |  | $ 52,443 |  | $ 45,553 |  | $ 43,231 |  | $ 42,587 |  | $ 40,446 |  | $ 41,430 |  | $ 37,419 |  | $ 195,336 | $ 161,882 | $ 130,754
Total net realized and unrealized (losses) gains | $ (37,935) | [2] | $ (4,787) | [2] | $ (1,652) | [2] | $ (10,549) | [2] | $ (1,128) | [2] | $ 6,798 | [2] | $ 1,734 | [2] | $ (1,045) | [2] | (54,923) | 6,359 | (4,937)
Total investment revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 140,413 | 168,241 | 125,817
Tax on investment income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 19,560 | 45,588 | 30,621
Total investment income, after federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 120,853 | $ 122,653 | $ 95,196
Investments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Return on Equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.90% | 7.50% | 6.50%
Standard Commercial Lines [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 109,104 | $ 149,514 | $ 146,435
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 86,192 | $ 97,184 | $ 95,183
Combined Ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 94.30% | 91.60% | 91.20%
Return on Equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.90% | 6.10% | 6.40%
Standard Personal Lines [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12,764 | $ 11,104 | $ 12,419
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,084 | $ 7,217 | $ 8,072
Combined Ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 95.80% | 96.20% | 95.60%
Return on Equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.60% | 0.40% | 0.60%
Excess And Surplus Operations [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (695) | $ (6,282) | $ (6,921)
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (549) | $ (4,083) | $ (4,499)
Combined Ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.30% | 103.00% | 103.40%
Return on Equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.00% | (0.30%) | (0.30%)
[1] | Results for the fourth quarter of 2017 include the impact of the $20.2 million write off of deferred tax assets required with the implementation of Tax Reform. See Note 13. "Federal Income Taxes" above for additional information.
[2] | Effective January 1, 2018, changes in unrealized gains and losses on our equity portfolio are recognized in income through "Net unrealized losses on equity securities" on our Consolidated Statements of Income, as a result of our adoption of ASU 2016-01. See Note 3. "Adoption of Accounting Pronouncements" above.

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