Note 3 - Debt Securities (Details Textual) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Number of Securities in Unrealized Loss Position	6	17
Percentage of Combined Depreciation of Combined Reported Value of Aggregate Securities Portfolio	0.12%	0.10%
Number of Securities in Unrealized Loss Position, Greater than or Equal to One Year	1
Security Owned and Pledged as Collateral, Fair Value, Total	$ 36,560	$ 27,870

Represents the number of securities in unrealized loss position.

No definition available.

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Namespace Prefix:	fcbc_
Data Type:	xbrli:integerItemType
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Period Type:	instant

- Definition

Number of investment positions that have been in a continuous unrealized loss position for greater than or equal to a year.

+ References

No definition available.

+ Details

Name:	fcbc_NumberOfSecuritiesInUnrealizedLossPositionGreaterThanOrEqualToOneYear
Namespace Prefix:	fcbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of combined depreciation of combined reported value of aggregate securities portfolio.

+ References

No definition available.

+ Details

Name:	fcbc_PercentageOfCombinedDepreciationOfCombinedReportedValueOfAggregateSecuritiesPortfolio
Namespace Prefix:	fcbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

+ Details

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