Fair Value Measurements, Quantitative Information (Details) $ in Thousands	6 Months Ended
Jun. 30, 2016 USD ($)
Impaired Loan [Member] \| Residential 1st Mortgage [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 317
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Impaired Loan [Member] \| Residential 1st Mortgage [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	0.00%
Impaired Loan [Member] \| Residential 1st Mortgage [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	4.00%
Impaired Loan [Member] \| Residential 1st Mortgage [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Impaired Loan [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 85
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Impaired Loan [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	1.00%
Impaired Loan [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Impaired Loan [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	2.00%
Impaired Loan [Member] \| Agricultural [Member] \| Income Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 298
Unobservable inputs	Capitalization Rate
Impaired Loan [Member] \| Agricultural [Member] \| Income Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Impaired Loan [Member] \| Agricultural [Member] \| Income Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Impaired Loan [Member] \| Agricultural [Member] \| Income Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Impaired Loan [Member] \| Agricultural [Member] \| Collateral Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 211
Unobservable inputs	Collateral Value
Impaired Loan [Member] \| Agricultural [Member] \| Collateral Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Collateral value	10.00%
Impaired Loan [Member] \| Agricultural [Member] \| Collateral Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Collateral value	10.00%
Impaired Loan [Member] \| Agricultural [Member] \| Collateral Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Collateral value	10.00%
Impaired Loan [Member] \| Commercial [Member] \| Income Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 849
Unobservable inputs	Capitalization Rate
Impaired Loan [Member] \| Commercial [Member] \| Income Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Impaired Loan [Member] \| Commercial [Member] \| Income Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Impaired Loan [Member] \| Commercial [Member] \| Income Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Capitalization rate	16.00%
Other Real Estate [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member]
Quantitative Information [Abstract]
Fair value	$ 779
Unobservable inputs	Adjustment for Difference Between Comparable Sales
Other Real Estate [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%
Other Real Estate [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Maximum [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%
Other Real Estate [Member] \| Home Equity Lines and Loans [Member] \| Sales Comparison Approach [Member] \| Weighted Average [Member]
Quantitative Information [Abstract]
Adjustment for difference between comparable sales	10.00%

Percentage of adjustment to the collateral value, used as an input to measure fair value.

No definition available.

Name:	fmcb_FairValueInputsCollateralValue
Namespace Prefix:	fmcb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

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=66048111&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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- 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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- Details

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