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3fbss_AdditionalSafeHarborContributionByEmployerPercentfbss_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsetruefalse00falsefalsefalse2falsetruefalse00falsefalsefalse3truetruefalse0.060.06falsefalsefalse4falsetruefalse00falsefalsefalse5falsetruefalse00falsefalsefalsenum:percentItemTypepureThe percentage of additional safe harbor contribution made by employer.No definition available.false0Additional safe harbor contribution by employer, percent (in hundredths)9false 3us-gaap_DefinedContributionPlanCostRecognizedus-gaap_truedebitdurationfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse180000180USD$falsetruefalse2truefalsefalse188000188USD$falsetruefalse3truefalsefalse341000341USD$falsetruefalse4truefalsefalse359000359USD$falsetruefalse5falsefalsefalse00falsefalsefalsexbrli:monetaryItemTypemonetaryThe amount of the cost recognized during the period for defined contribution plans.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB 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This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 30 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 6, 7 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Deferred compensation expense14false 3us-gaap_CashSurrenderValueOfLifeInsuranceus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse11940001194USD$falsetruefalse2falsefalsefalse00falsefalsefalse3truefalsefalse11940001194USD$falsetruefalse4falsefalsefalse00falsefalsefalse5truefalsefalse11800001180USD$falsetruefalsexbrli:monetaryItemTypemonetaryCarrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6812-107765 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Technical Bulletin (FTB) -Number 85-4 -Paragraph 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false2Cash surrender value of life insurancefalseEmployee Benefit Plans (Details) (USD $)ThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://fauquierbank.com/role/EmployeeBenefitPlansDetails514