Fair Value Measurements, Quantitative Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($)
Residential 1st Mortgages [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 329
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Residential 1st Mortgages [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	1.00%
Residential 1st Mortgages [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	5.00%
Residential 1st Mortgages [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	3.00%
Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 125
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	1.00%
Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	3.00%
Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Agricultural [Member] \| Income Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 298
Unobservable inputs	Capitalization Rate
Agricultural [Member] \| Income Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Agricultural [Member] \| Income Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Agricultural [Member] \| Income Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Commercial [Member] \| Income Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 752
Unobservable inputs	Capitalization Rate
Commercial [Member] \| Income Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Commercial [Member] \| Income Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Commercial [Member] \| Income Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Consumer [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 5
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Consumer [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Consumer [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Consumer [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Real Estate Construction [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 2,441
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Real Estate Construction [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%
Real Estate Construction [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%
Real Estate Construction [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

No definition available.

+ Details

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

- Definition

Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value.

+ References

+ Details

Name:	us-gaap_FairValueInputsComparabilityAdjustments
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Description of the inputs and valuation technique(s) used to measure fair value.

+ References

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
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- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
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Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
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- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=fmcb_AgriculturalPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_IncomeApproachValuationTechniqueMember
Namespace Prefix:
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- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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