Summary of Significant Accounting Policies, Nature of Operations and Basis of Consolidation (Details)	Dec. 31, 2023 Office ATMs
Nature of Operations and Basis of Consolidation [Abstract]
Number of banking offices \| Office	29
Number of ATMs \| ATMs	3

Number of banking offices operating by the entity.

No definition available.

Name:	fmcb_NumberOfOperatingBankingOffices
Namespace Prefix:	fmcb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant