Deposits - Composition of Network Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Reciprocal [Abstract]
CDARS	$ 21,413	$ 7,622
ICS	0	0
DDM	52,365	30,544
Total network deposits	73,778	38,166
One Way [Abstract]
CDARS	2,160	2,434
ICS	110,900	110,929
DDM	60,000	60,000
Total network deposits	$ 173,060	$ 173,363

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