Deposits (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Certificates of deposit [Abstract]
Certificates of deposit less than or equal to $250,000	$ 323,918	$ 330,475
Certificates of deposit greater than $250,000	385,984	385,072
Total certificates of deposit	709,902	715,547
Maturities for Certificates of Deposit [Abstract]
2025	621,710
2026	83,838
2027	3,102
2028	956
2029	220
2030	76
Total certificates of deposit	709,902	715,547
Overdrawn deposit balances classified as consumer loans	$ 138	$ 156

Amount of overdrawn time deposit liabilities classified as consumer loans.

No definition available.

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- Definition

The amount of time deposit liabilities, including certificates of deposit in denominations of $250,000 or more.

+ References

No definition available.

+ Details

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- Definition

The amount of time deposit liabilities, including certificates of deposit in denominations of less than or equal to $250,000.

+ References

No definition available.

+ Details

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Namespace Prefix:	fmcb_
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Period Type:	instant

- References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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- Definition

Amount of time deposit maturing in remainder of current fiscal year. Time deposit includes, but is not limited to, certificate of deposit.

+ References

No definition available.

+ Details

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- Definition

Amount of time deposit maturing in fifth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 10
-Topic 470
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481544/470-10-50-1

+ Details

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- Definition

Amount of time deposit maturing in fourth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Period Type:	instant

- Definition

Amount of time deposit maturing in next fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Period Type:	instant

- Definition

Amount of time deposit maturing in third fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Period Type:	instant

- Definition

Amount of time deposit maturing in second fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

- Definition

Amount of time deposit liabilities, including certificates of deposit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 405
-Topic 942
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478353/942-405-50-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(12))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

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