Fair value disclosure of loans and lines of credit made to farmers to finance agricultural production.

No definition available.

Name:	fmcb_AgriculturalFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value disclosure of other real estate related to Agricultural Real Estate.

+ References

No definition available.

+ Details

Name:	fmcb_AgriculturalRealEstateOtherRealEstate
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value disclosure of loans and lines of credit made to farmers to finance agricultural real estate.

+ References

No definition available.

+ Details

Name:	fmcb_AgricultureRealEstateFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value disclosure of secured and unsecured loans for purposes such as seasonal working capital needs, inventory financing, equipment purchases and acquisitions.

+ References

No definition available.

+ Details

Name:	fmcb_CommercialLoansFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

Name:	fmcb_CorporateSecuritiesFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unobservable input adjustments applicable to valuation technique.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. Government Agencies Debentures, notes and other debt securities issued by US government agencies, for example but not limited to, Government National Mortgage Association (GNMA or Ginnie Mae) which have been categorized as available-for-sale. Excludes US treasury Securities. Government Sponsored Entities (GESs) Debentures, bonds and other debt securities issued by US government sponsored entities, for example, but not limited to, Federal Home Loan Mortgage Corporation (FHLMC or Freddie Mac), Federal National Mortgage Association (FNMA or Fannie Mae), and the Federal Home Loan Bank (FHLB) which have been categorized as available-for-sale.

+ References

No definition available.

+ Details

Name:	fmcb_GovernmentAgencyGovernmentSponsoredEntitiesFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value disclosure of revolving, open-end loan extended under a line of credit and secured by the borrower's residential property.

+ References

No definition available.

+ Details

Name:	fmcb_HomeEquitiesLinesAndLoansFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents impaired loan receivable as presented on the statement of financial position which may include mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts, or any other loans which are due the Company as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	fmcb_ImpairedLoansFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

Name:	fmcb_ObligationOfStatesAndPoliticalSubdivisionsFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

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

- Definition

Fair value disclosure of other real estate related to construction.

+ References

No definition available.

+ Details

Name:	fmcb_RealEstateConstructionsFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value disclosure of loans to purchase or refinance residential real estate for example, but not limited to a home, in which the real estate itself serves as collateral for the loan.

+ References

No definition available.

+ Details

Name:	fmcb_Residential1StMortgageFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total fair value disclosure of other real estate assets.

+ References

No definition available.

+ Details

Name:	fmcb_TotalOtherRealEstateFairValueDisclosure
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

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

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ 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=25499696&loc=d3e19207-110258

+ Details

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

- Definition

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

+ References

+ Details

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

- Details

Name:	us-gaap_LoanAndLeaseReceivablesImpairedAbstract
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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Mortgage-Backed Securities

-URI http://asc.fasb.org/extlink&oid=6517959

+ Details

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

- Definition

Fair value portion of other assets.

+ References

No definition available.

+ Details

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

Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified				6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Jun. 30, 2014 Residential 1st Mortgages [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Residential 1st Mortgages [Member] Minimum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Residential 1st Mortgages [Member] Maximum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Residential 1st Mortgages [Member] Weighted Average [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Home Equity Lines and Loans [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Home Equity Lines and Loans [Member] Minimum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Home Equity Lines and Loans [Member] Maximum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Home Equity Lines and Loans [Member] Weighted Average [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Agricultural [Member] Income Approach [Member]	Jun. 30, 2014 Agricultural [Member] Minimum [Member] Income Approach [Member]	Jun. 30, 2014 Agricultural [Member] Maximum [Member] Income Approach [Member]	Jun. 30, 2014 Agricultural [Member] Weighted Average [Member] Income Approach [Member]	Jun. 30, 2014 Commercial [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Commercial [Member] Minimum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Commercial [Member] Maximum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Commercial [Member] Weighted Average [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Real Estate Construction [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Real Estate Construction [Member] Minimum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Real Estate Construction [Member] Maximum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Real Estate Construction [Member] Weighted Average [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Agricultural Real Estate [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Agricultural Real Estate [Member] Minimum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Agricultural Real Estate [Member] Maximum [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Agricultural Real Estate [Member] Weighted Average [Member] Sales Comparison Approach [Member]	Jun. 30, 2014 Recurring [Member]	Dec. 31, 2013 Recurring [Member]	Jun. 30, 2013 Recurring [Member]	Jun. 30, 2014 Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2013 Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2013 Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2014 Recurring [Member] Other Observable Inputs (Level 2) [Member]	Dec. 31, 2013 Recurring [Member] Other Observable Inputs (Level 2) [Member]	Jun. 30, 2013 Recurring [Member] Other Observable Inputs (Level 2) [Member]	Jun. 30, 2014 Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2013 Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Jun. 30, 2013 Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Jun. 30, 2014 Nonrecurring [Member]	Dec. 31, 2013 Nonrecurring [Member]	Jun. 30, 2013 Nonrecurring [Member]	Jun. 30, 2014 Nonrecurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2013 Nonrecurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2013 Nonrecurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2014 Nonrecurring [Member] Other Observable Inputs (Level 2) [Member]	Dec. 31, 2013 Nonrecurring [Member] Other Observable Inputs (Level 2) [Member]	Jun. 30, 2013 Nonrecurring [Member] Other Observable Inputs (Level 2) [Member]	Jun. 30, 2014 Nonrecurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2013 Nonrecurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Jun. 30, 2013 Nonrecurring [Member] Significant Unobservable Inputs (Level 3) [Member]
Available-for-Sale Securities [Abstract]
Government Agency & Government-Sponsored Entities																												$ 18,424	$ 28,436	$ 26,482	$ 13,412	$ 23,394	$ 21,416	$ 5,012	$ 5,042	$ 5,066	$ 0	$ 0	$ 0
Obligations of States and Political Subdivisions																														5,612			0			0			5,612
Mortgage Backed Securities																												326,335	324,929	392,574	0	0	0	326,335	324,929	392,574	0	0	0
Corporate Securities																												54,661	49,380	49,560	8,982	8,191	8,122	45,679	41,189	41,438	0	0	0
Other																												2,312	1,894	1,186	2,002	1,584	876	310	310	310	0	0	0
Fair/Book Value, Total	401,732	404,639	475,414																									401,732	404,639	475,414	24,396	33,169	30,414	377,336	371,470	439,388	0	0	5,612
Impaired Loans [Abstract]
Agriculture Real Estate																																										1,143			0			0			1,143
Residential 1st Mortgages																																								354	614	283	0	0	0	0	0	0	354	614	283
Home Equity Lines and Loans																																								729	551	184	0	0	0	0	0	0	729	551	184
Agricultural																																								354	366	672	0	0	0	0	0	0	354	366	672
Commercial																																								807	820	216	0	0	0	0	0	0	807	820	216
Total Impaired Loans																																								2,244	2,351	2,498	0	0	0	0	0	0	2,244	2,351	2,498
Other Real Estate [Abstract]
Real Estate Construction																																								2,441	2,399	2,399	0	0	0	0	0	0	2,441	2,399	2,399
Agricultural Real Estate																																								853	2,212		0	0		0	0		853	2,212
Total Other Real Estate																																								3,294	4,611	2,399	0	0	0	0	0	0	3,294	4,611	2,399
Total Assets Measured at Fair Value On a Non-Recurring Basis				354				729				354				807				2,441				853																5,538	6,962	4,897	0	0	0	0	0	0	5,538	6,962	4,897
Quantitative Information [Abstract]
Fair Value				$ 354				$ 729				$ 354				$ 807				$ 2,441				$ 853																$ 5,538	$ 6,962	$ 4,897	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5,538	$ 6,962	$ 4,897
Valuation Technique				Sales Comparison Approach				Sales Comparison Approach				Income Approach				Sales Comparison Approach				Sales Comparison Approach				Sales Comparison Approach
Unobservable Inputs				Adjustment for Difference Between Comparable Sales				Adjustment for Difference Between Comparable Sales				Capitalization Rate				Adjustment for Difference Between Comparable Sales				Adjustment for Difference Between Comparable Sales				Adjustment for Difference Between Comparable Sales
Range, Weighted Avg. (in hundredths)					11.00%	21.00%	14.00%		2.00%	14.00%	11.00%		14.00%	14.00%	14.00%		13.00%	13.00%	13.00%		10.00%	10.00%	10.00%		10.00%	10.00%	10.00%