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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | $ 52,443 | $ 40,446 | $ 141,227 | $ 119,295
Fixed Income Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 45,088 | 38,865 | 130,903 | 113,424
Equity Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 2,079 | 1,605 | 5,876 | 4,492
Short-Term Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 867 | 396 | 2,001 | 1,023
Other Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 7,211 | 2,659 | 10,868 | 9,493
Investment Expenses [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | $ (2,802) | $ (3,079) | $ (8,421) | $ (9,137)

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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=114873790&loc=SL114874131-224263 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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