Investment Securities, Proceeds From Sales (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Proceeds from sales and calls of securities [Abstract]
Proceeds	$ 475	$ 2,988
Gains	1fmcb_SecuritiesGrossRealizedGains	3fmcb_SecuritiesGrossRealizedGains
Losses	$ 0fmcb_SecuritiesGrossRealizedLosses	$ 0fmcb_SecuritiesGrossRealizedLosses

This item represents the gross profit realized on the sales and calls of debt or equity securities.

No definition available.

Name:	fmcb_SecuritiesGrossRealizedGains
Namespace Prefix:	fmcb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration