XML 71 R59.htm IDEA: XBRL DOCUMENT v3.7.0.1

Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Period of maturity as classifies as short-term borrowings	90 days
Loans held for sale | Nonrecurring basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Non recurring fair value adjustments on loans held for sale	$ 0	$ 0
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Period under consideration for valuation of real estate collateral	12 months
Period under consideration for valuation of business equipment	1 year
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Period under consideration for valuation of house or building in the process of construction	1 year

X

- Definition

Period of appraisal of property to consider different method to measure fair value.

+ References

No definition available.

+ Details

Name:	fxnc_PeriodOfAppraisalOfPropertyToConsiderDifferentMethodToMeasureFairValue
Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Period of maturity as classifies as short term borrowing.

+ References

No definition available.

+ Details

Name:	fxnc_PeriodOfMaturityAsClassifiesAsShortTermBorrowing
Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Period used to determine value of business equipment.

+ References

No definition available.

+ Details

Name:	fxnc_PeriodUsedToDetermineValueOfBusinessEquipment
Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Maximum period used to determine value of real estate collateral.

+ References

No definition available.

+ Details

Name:	fxnc_PeriodUsedToDetermineValueOfRealEstateCollateral
Namespace Prefix:	fxnc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

+ Details

Name:	us-gaap_AssetsFairValueAdjustment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_InvestmentTypeAxis=fxnc_LoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: