No definition available.

Name:	fmcb_ExecutiveRetirementPlanLifeInsuranceArrangementsAndSeniorManagementRetentionPlanAbstract
Namespace Prefix:	fmcb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Net investment Gain (Loss) on Non-Qualified Deferred Compensation balance held in a rabbi trust recorded in non-interest income. This line item is offset by an identical entry to non-interest expense resulting in no impact to net income.

+ References

No definition available.

+ Details

Name:	fmcb_NetGainLossNonQualifiedDeferredCompensationPlanInvestmentsNonInterestIncome
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Element presents the period after the termination of plan for the account balances to be liquidated and paid out to each participant, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	fmcb_PeriodForAccountBalancesToBeLiquidatedAndPaidOutToEachParticipant
Namespace Prefix:	fmcb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of common stock issued to a trust (for example, but not limited to, rabbi trust) set up specifically to accumulate stock for the sole purpose of distribution to participating employees.

+ References

No definition available.

+ Details

Name:	us-gaap_CommonStockSharesHeldInEmployeeTrust
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 25
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480637/718-40-25-12

+ Details

Name:	us-gaap_CommonStockSharesHeldInEmployeeTrustShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 710
-SubTopic 10
-Name Accounting Standards Codification
-Section 30
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483043/710-10-30-1

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualRecordedLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_TitleOfIndividualAxis=srt_ExecutiveOfficerMember
Namespace Prefix:
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- Details

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- Details

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Namespace Prefix:
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- Details

Name:	srt_TitleOfIndividualAxis=srt_ManagementMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationShareBasedPaymentsMember
Namespace Prefix:
Data Type:	na
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Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
Employee Benefit Plans (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Net gain on deferred compensation benefits	$ 833	$ 1,158
Executive Officers [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Employer contribution	0	2,200
Carrying value of liability	$ 60,800		$ 61,400
Common stock held as investments in Rabbi Trust of ERP (in shares)	48,892		48,877
Common stock held as investments in Rabbi Trust of ERP, historical cost basis amount	$ 31,600		$ 31,800
Net gain on deferred compensation benefits	$ 600	1,000
Executive Officers [Member] \| Minimum [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Period for account balances to be liquidated and paid out to each participant	12 months
Executive Officers [Member] \| Maximum [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Period for account balances to be liquidated and paid out to each participant	24 months
Senior Level Employees [Member] \| Senior Management Retention Plan [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Employer contribution	$ 0	1,100
Carrying value of liability	$ 20,800		$ 21,200
Common stock held as investments in Rabbi Trust of ERP (in shares)	18,474		19,647
Common stock held as investments in Rabbi Trust of ERP, historical cost basis amount	$ 14,200		$ 14,600
Net gain on deferred compensation benefits	$ 200	$ 200
Senior Level Employees [Member] \| Minimum [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Period for account balances to be liquidated and paid out to each participant	12 months
Senior Level Employees [Member] \| Maximum [Member]
Executive Retirement Plan, Life Insurance Arrangements and Senior Management Retention Plan [Abstract]
Period for account balances to be liquidated and paid out to each participant	24 months