Loans and Allowance for Loan Losses, Troubled Debt Restructurings (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 Contract Property Loan	Mar. 31, 2014 Contract	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0fbss_ModificationsNumberOfContracts
Troubled debt restructurings, pre-modification outstanding recorded investment	$ 0fbss_PreModificationRecordedInvestment
Number of TDR loans secured by business assets	13
TDR loans value	7,927
Number of TDR loans current and performing	11
TDR loans current and performing	7,402fbss_TdrLoansCurrentAndPerforming
Number of TDR loans not performing in accordance with the modified terms	2
TDR loans not performing in accordance with modified terms	525
Non-performing Assets, Restructured Loans Still Accruing and Loans Contractually Past Due [Abstract]
Number of residential foreclosed properties in possession	0
Mortgage Loans in Process of Foreclosure, Amount	543
Number of residential foreclosures in process	2
Non-accrual loans	1,593	2,002	1,227
Other real estate owned	1,406us-gaap_OtherRealEstate	1,406us-gaap_OtherRealEstate	1,406us-gaap_OtherRealEstate
Non-performing corporate bond investments, at fair value	0	1,861	0
Total non-performing assets	2,999fbss_NonPerformingAssets	5,269fbss_NonPerformingAssets	2,633fbss_NonPerformingAssets
Restructured loans still accruing	7,402fbss_RestructuredLoansStillAccruing	8,598fbss_RestructuredLoansStillAccruing	7,431fbss_RestructuredLoansStillAccruing
Loans past due 90 or more days and still accruing	2,721fbss_StudentLoans90PdStillAccruing	7,017fbss_StudentLoans90PdStillAccruing	4,551fbss_StudentLoans90PdStillAccruing
Loans past due 90 or more days and still accruing	2	358	0
Total non-performing and other risk assets	13,124fbss_NonPerformingAndOtherRiskAssets	21,242fbss_NonPerformingAndOtherRiskAssets	14,615fbss_NonPerformingAndOtherRiskAssets
Allowance for loan losses to total loans (in hundredths)	1.21%	1.49%	1.22%
Non-accrual loans to total loans (in hundredths)	0.36%	0.45%	0.28%
Allowance for loan losses to non-accrual loans (in hundredths)	338.10%	331.22%	439.36%
Total non-accrual loans and restructured loans still accruing to total loans (in hundredths)	2.02%	2.38%	1.97%
Allowance for loan losses to non-accrual loans and restructured loans still accruing (in hundredths)	59.88%	62.56%	62.27%
Total non-performing assets to total assets (in hundredths)	0.50%	0.87%	0.43%
Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	1
Troubled debt restructurings, pre-modification outstanding recorded investment	0	65
Troubled debt restructurings, post-modification outstanding recorded investment	0	65
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Construction and Land [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment		0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment		0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	0	0
Student US Government Guaranteed [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings, number of contracts	0	0
Troubled debt restructurings, pre-modification outstanding recorded investment	0	0
Troubled debt restructurings, post-modification outstanding recorded investment	0	0
Troubled debt restructurings that subsequently defaulted, number of contracts	0	0
Troubled debt restructurings that subsequently defaulted, pre-modification outstanding recorded investment		0
Troubled debt restructurings that subsequently defaulted, post-modification outstanding recorded investment	$ 0	$ 0

The percentage of allowance for loan losses to non-accrual loans and restructured loans still accruing.

No definition available.

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- Definition

The percentage of allowance for loan losses to non-accrual loans.

+ References

No definition available.

+ Details

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- Definition

The percentage of allowance for loan losses to total loans.

+ References

No definition available.

+ Details

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default related to pre-modification recorded investment.

+ References

No definition available.

+ Details

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- Definition

Other loans past due 90 or more days and still accruing

+ References

No definition available.

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

No definition available.

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- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process (2015 taxonomy)

+ References

No definition available.

+ Details

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- Definition

The percentage of non-accrual loans to total loans.

+ References

No definition available.

+ Details

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- Definition

Carrying amount of non-performing and other risk assets.

+ References

No definition available.

+ Details

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- Definition

Carrying amount as of the balance sheet date of non-performing assets, including non-accrual loans, other real estate, foreclosed assets, and non-performing corporate bond investments.

+ References

No definition available.

+ Details

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- Definition

Investment in non-performing corporate bond investments, at fair value.

+ References

No definition available.

+ Details

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- Definition

Number of residential foreclosed properties in possession.

+ References

No definition available.

+ Details

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- Definition

Number of residential foreclosures in process.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of troubled debt restructuring loans that are current and performing in accordance with modified terms.

+ References

No definition available.

+ Details

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Namespace Prefix:	fbss_
Data Type:	xbrli:integerItemType
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- Definition

Represents the number of troubled debt restructuring loans that are not performing in accordance with modified terms.

+ References

No definition available.

+ Details

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- Definition

Represents the number of troubled debt restructuring loans that are secured by business assets.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
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- Definition

Amount of investment in financing receivables (after modification) modified by troubled debt restructurings.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Amount of investment in financing receivables (before modification) modified by troubled debt restructurings.

+ References

No definition available.

+ Details

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Namespace Prefix:	fbss_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Carrying amount of restructured loans still accruing related to troubled debt restructuring.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount of Student Loans (U. S. Government guaranteed past due 90 or more days and still accruing

+ References

No definition available.

+ Details

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Namespace Prefix:	fbss_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Represents the carrying value of troubled debt restructuring loans that are current and performing in accordance with modified terms.

+ References

No definition available.

+ Details

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- Definition

Represents the carrying value of troubled debt restructuring loans that are not performing in accordance with modified terms.

+ References

No definition available.

+ Details

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- Definition

The percentage of total non-accrual loans and restructured loans still accruing to total loans.

+ References

No definition available.

+ Details

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- Definition

The percentage of total non-performing assets to total assets.

+ References

No definition available.

+ Details

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- Details

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

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- Definition

Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10(4))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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