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Investments (Net Investment Income) (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
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned | $ 57,594 | $ 55,826 | $ 58,505 | $ 50,618 | $ 54,109 | $ 52,443 | $ 45,553 | $ 43,231 | $ 222,543 | $ 195,336 | $ 161,882
Fixed Income Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned |  |  |  |  |  |  |  |  | 203,255 | 178,104 | 153,230
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned |  |  |  |  |  |  |  |  | 6,996 | 7,764 | 6,442
Short-term Investments [Member] |  |  |  |  |  |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned |  |  |  |  |  |  |  |  | 6,653 | 3,472 | 1,526
Other Investment Portfolio [Member] |  |  |  |  |  |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned |  |  |  |  |  |  |  |  | 18,778 | 17,799 | 12,871
Investment Expenses [Member] |  |  |  |  |  |  |  |  |  |  |
Statement [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net investment income earned |  |  |  |  |  |  |  |  | $ (13,139) | $ (11,803) | $ (12,187)

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- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 + Details
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