Subsequent Events (Details) - Bank of Rio Vista [Member] - Subsequent Event [Member]	Feb. 27, 2018 USD ($) shares
Subsequent Event [Line Items]
Number of additional shares acquired (in shares)	8
Value of additional shares acquired \| $	$ 95,200
Total ownership of shares (in shares)	1,586
Percentage of ownership of common shares outstanding	39.65%

Number of additional shares acquired under business acquisition.

No definition available.

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Namespace Prefix:	fmcb_
Data Type:	xbrli:sharesItemType
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- Definition

Total number of shares of equity of the acquired entity owned by the acquiring entity after acquisition.

+ References

No definition available.

+ Details

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

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- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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- Details

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- Details

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