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Investments - Impairment Losses on Held-to-maturity Security - Narrative (Details) | 6 Months Ended
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Jun. 30, 2018 USD ($)
Investments Debt And Equity Securities [Abstract] |
Cumulative impairment loss held-to-maturity security | $ 0

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- Definition Amount, before tax, of other-than-temporary impairment (OTTI) on investment in debt security measured at amortized cost (held-to-maturity), recognized in earnings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562 + Details
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