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Investments (Narrative) (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Investments [Line Items] |  |  |
Credit-related net investment impairment losses | $ 0 | $ 0 | $ 500,000
Other that temporary impairment credit losses recognized in earnings | 1,600,000 |  |
nongovernmentalissuerover10%ofequity | $ 0 | 0 |
Maximum |  |  |
Schedule of Investments [Line Items] |  |  |
Regional community bank stocks, percent of average trading volumes | 0.20% |  |
First National Corporation (FXNC) [Domain] | Maximum |  |  |
Schedule of Investments [Line Items] |  |  |
Equity ownership positions in the community bank holding companies | 4.00% |  |
Eagle Financial Services, Inc. (EFSI) [Domain] | Maximum |  |  |
Schedule of Investments [Line Items] |  |  |
Equity ownership positions in the community bank holding companies | 1.50% |  |
Asset Pledged as Collateral [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Debt Securities, Available-for-sale, Restricted | $ 510,000,000 | $ 429,000,000 |

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