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Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Net investment gains (losses) | $ 911,243 | $ 425,653 | $ (770,198) | $ 1,037,844 |
Equity securities | 5,664,247 |  | 5,664,247 |  | $ 7,590,755
Fair value, recurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Fair value, level 1 to level 2 transfers, amount |  |  | 0 | 0 |
Fair value, level 2 to level 1 transfers, amount |  |  | 0 | 0 |
Equity securities | 5,664,247 |  | 5,664,247 |  | $ 7,590,755
Fair value, nonrecurring [Member] |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Assets measured at fair value on a nonrecurring basis | 0 | 0 | 0 | 0 |
Liabilities measured at fair value on a nonrecurring basis | $ 0 | $ 0 | $ 0 | $ 0 |

X
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- Definition The net gains or losses on investments during the period, also including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. + References No definition available. + Details
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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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