Investment Securities, Proceeds From Sales (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Proceeds from sales and calls of securities [Abstract]
Proceeds	$ 2,988	$ 45,259
Gains	3	749
Losses	$ 0	$ 14

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