Investment Securities, Proceeds From Sales (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Proceeds from sales and calls of securities [Abstract]
Proceeds	$ 6,969	$ 4,356	$ 9,917	$ 49,615
Gains	31	154	34	903
Losses	$ 0	$ 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