Deposits - Composition of Network Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Reciprocal [Abstract]
CDARS	$ 11,031	$ 21,413
ICS	100,749	0
DDM	62,219	52,365
Total network deposits	173,999	73,778
One Way [Abstract]
CDARS	2,162	2,160
ICS	0	110,900
DDM	0	60,000
Total network deposits	$ 2,162	$ 173,060

Certificate of Deposit Account Registry Service, a special type of certificate of deposit whereby the participating bank accepts deposits in excess of the FDIC insured maximum and places the deposits through a network to member banks in the CDARS(R) network in increments of less than the FDIC insured maximum to provide the depositor full FDIC insurance coverage.

No definition available.

Name:	bmrc_TimeDepositsCertificateOfDepositAccountRegistryServiceCDARS
Namespace Prefix:	bmrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant