Name:	fmcb_TimeDepositMaturitiesYearFourAndBeyond
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The amount of time deposit liabilities, including certificates of deposit in denominations of $250,000 or more.

No definition available.

Name:	fmcb_TimeDeposits250000OrMore
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Data Type:	xbrli:monetaryItemType
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The amount of time deposit liabilities, including certificates of deposit in denominations of less than or equal to $250,000.

No definition available.

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Data Type:	xbrli:monetaryItemType
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- References

No definition available.

Name:	us-gaap_DepositsByTypeAbstract
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- References

No definition available.

Name:	us-gaap_MaturitiesOfTimeDepositsAbstract
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Data Type:	xbrli:stringItemType
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Amount of time deposit maturing in remainder of current fiscal year. Time deposit includes, but is not limited to, certificate of deposit.

No definition available.

Name:	us-gaap_TimeDepositMaturitiesRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of time deposit maturing in next fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601

Name:	us-gaap_TimeDepositMaturitiesYearOne
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Amount of time deposit maturing in third fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Name:	us-gaap_TimeDepositMaturitiesYearThree
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of time deposit maturing in second fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Name:	us-gaap_TimeDepositMaturitiesYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of time deposit liabilities, including certificates of deposit.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878