Investment Securities, Proceeds from Sales (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Proceeds from sales and calls of securities [Abstract]
Proceeds	$ 4,060	$ 6,969	$ 4,535	$ 9,917
Gains	5	31	6	34
Losses	$ 0	$ 0	$ 0	$ 0

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