Leases, Summary (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Leases [Abstract]
Operating lease ROU assets	$ 4,050,000.00	$ 4,800,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Operating lease liability	$ 4,133,000	$ 4,920,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]	fmcb:InterestPayableAndOtherLiabilities	fmcb:InterestPayableAndOtherLiabilities
Operating lease cost	$ 739,000	$ 833,000	$ 836,000
Minimum [Member]
Operating Leases [Abstract]
Remaining lease term	1 year
Lease extension option term	5 years
Maximum [Member]
Operating Leases [Abstract]
Remaining lease term	10 years
Lease extension option term	10 years