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Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Feb. 29, 2024
Jun. 30, 2023
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2023    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-33572    
Entity Registrant Name Bank of Marin Bancorp    
Entity Incorporation, State or Country Code CA    
Entity Tax Identification Number 20-8859754    
Entity Address, Address Line One 504 Redwood Blvd.    
Entity Address, Address Line Two Suite 100    
Entity Address, City or Town Novato    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94947    
City Area Code 415    
Local Phone Number 763-4520    
Title of 12(g) Security Common Stock, No Par Value    
Trading Symbol BMRC    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Smaller Reporting Company false    
Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction Flag false    
Entity Shell Company false    
Entity Public Float     $ 269
Entity Common Stock, Shares Outstanding   16,193,342  
Documents Incorporated by Reference
Portions of the registrant's Proxy Statement for the Annual Meeting of Shareholders to be held on May 14, 2024 are incorporated by reference into Part III.
    
Entity Central Index Key 0001403475    
Document Fiscal Year Focus 2023    
Document Fiscal Period Focus FY    
Amendment Flag false