Financing receivable amount of loans authorized.

No definition available.

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Namespace Prefix:	fbss_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Financing receivable number of loans authorized.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Number of foreclosed properties in possession or in the process of foreclosure.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

The number of troubled debt restructuring loans outstanding in the portfolio.

+ References

No definition available.

+ Details

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

- 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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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953682-111524

+ Details

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

- References

No definition available.

+ Details

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Period Type:	duration

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=fbss_SmallBusinessAdministrationCARESActPaycheckProtectionProgramMember
Namespace Prefix:
Data Type:	na
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Loans and Allowance for Loan Losses - Additional Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) Loan Property	Jun. 30, 2019 Loan Property	Jun. 30, 2020 USD ($) Loan Property	Jun. 30, 2019 Loan Property	Dec. 31, 2019 USD ($) Loan
Troubled Debt Restructurings [Abstract]
Number of Contracts		0		0
Number of TDR loans in the portfolio	6		6		5
TDR loans in the portfolio \| $	$ 8.6		$ 8.6		$ 2.5
Number of TDR loans current and performing	6		6		5
Number of TDRs with defaults occurring within 12 months of modification	0	0	0	0
Less Than 30 Days Past Due [Member]
Troubled Debt Restructurings [Abstract]
Number of TDR loans in the portfolio	194		194
TDR loans in the portfolio \| $	$ 92.8		$ 92.8
Residential Real Estate [Member]
Troubled Debt Restructurings [Abstract]
Number of foreclosed properties in possession or in process of foreclosure \| Property	0	0	0	0
Small Business Administration (SBA) CARES Act, Paycheck Protection Program [Member]
Financing Receivable Impaired [Line Items]
Financing receivable number of loans authorized	543		543
Financing receivable amount of loans authorized \| $	$ 52.8		$ 52.8