Troubled Debt Restructuring (Details)	9 Months Ended
Sep. 30, 2020 USD ($) integer	Sep. 30, 2019 USD ($) integer
Total [Member]
Number of contracts \| integer		7
Pre-modification outstanding recorded investment		$ 963,000
Post-modification outstanding recorded investment		$ 963,000
Real Estate [Member]
Number of contracts \| integer		2
Pre-modification outstanding recorded investment		$ 221,000
Post-modification outstanding recorded investment		$ 221,000
Commercial & Industrial - Non-Real Estate
Number of contracts \| integer		1
Pre-modification outstanding recorded investment		$ 20,000
Post-modification outstanding recorded investment		$ 20,000
Real Estate 1 [Member]
Number of contracts \| integer		1
Pre-modification outstanding recorded investment		$ 192,000
Post-modification outstanding recorded investment		$ 192,000
Home Equity
Number of contracts \| integer		1
Pre-modification outstanding recorded investment		$ 718,000
Post-modification outstanding recorded investment		$ 718,000
Consumer
Number of contracts \| integer	4	3
Pre-modification outstanding recorded investment	$ 26,000	$ 224,000
Post-modification outstanding recorded investment	$ 26	$ 3,000
Consumer 1
Number of contracts \| integer		4
Pre-modification outstanding recorded investment		$ 33,000
Post-modification outstanding recorded investment		$ 33,000

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

No definition available.

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Namespace Prefix:	fmbm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ 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=118936363&loc=SL6953676-111524

+ Details

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Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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