v3.26.1
Cover - shares
 6 Months Ended
Jun. 30, 2026
Jul. 31, 2026
Document Information Line Items    
Entity Central Index Key 0001085913  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Transition Report false  
Entity File Number 000-26099  
Entity Registrant Name FARMERS & MERCHANTS BANCORP  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 94-3327828  
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  
City Area Code 209  
Local Phone Number 367-2300  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   691,944
Amendment Flag false  
Document Fiscal Period Focus Q2  
Current Fiscal Year End Date --12-31