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Investments (Net Investment Income) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | $ 93,032 | $ 68,185 | $ 246,479 | $ 158,596
Investment Expense | (5,218) | (4,208) | (14,314) | (11,004)
Fixed Income Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 51,683 | 51,285 | 157,114 | 152,617
Commercial Mortgage Loans [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 683 | 245 | 1,892 | 463
Equity Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 2,955 | 1,948 | 8,425 | 5,523
Short-Term Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 64 | 244 | 204 | 1,830
Other Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | 42,865 | 18,671 | 93,158 | 9,167
Alternative Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Net investment income earned | $ 42,800 | $ 18,700 | $ 92,900 | $ 8,900

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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=120400993&loc=SL114874131-224263 + Details
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