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Segment Information (Income Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2022 | Mar. 31, 2021
Segment Reporting Information [Line Items] |  |
Net investment income | $ 72,602 | $ 69,716
Net realized and unrealized investment (losses) gains | (40,352) | 5,119
Total investment segment income, before federal income tax | 32,250 | 74,835
Tax on investment income | 5,613 | 14,448
Total investment segment income, after federal income tax | 26,637 | 60,387
Standard Commercial Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income, before federal income tax | 42,384 | 69,499
Underwriting income, after federal income tax | $ 33,483 | $ 54,904
Combined ratio | 93.60% | 88.20%
ROE Contribution | 5.00% | 8.60%
Standard Personal Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income, before federal income tax | $ 6,520 | $ 7,695
Underwriting income, after federal income tax | $ 5,151 | $ 6,079
Combined ratio | 91.00% | 89.60%
ROE Contribution | 0.80% | 1.00%
E&S Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income, before federal income tax | $ 6,925 | $ 516
Underwriting income, after federal income tax | $ 5,471 | $ 408
Combined ratio | 91.10% | 99.20%
ROE Contribution | 0.80% | 0.10%
Investments |  |
Segment Reporting Information [Line Items] |  |
ROE Contribution | 8.70% | 8.90%

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