Cover - shares	6 Months Ended
	Jun. 30, 2025	Jul. 31, 2025
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Amendment Flag	false
Document Period End Date	Jun. 30, 2025
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	Q2
Entity Information [Line Items]
Entity Registrant Name	FARMERS & MERCHANTS BANCORP
Entity Central Index Key	0001085913
Entity File Number	000-26099
Entity Tax Identification Number	94-3327828
Entity Incorporation, State or Country Code	DE
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Contact Personnel [Line Items]
Entity Address, Address Line One	111 W. Pine Street
Entity Address, City or Town	Lodi
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95240
Entity Phone Fax Numbers [Line Items]
City Area Code	209
Local Phone Number	367-2300
Entity Listings [Line Items]
Entity Common Stock, Shares Outstanding		722,351