Deposits - Composition of Network Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Reciprocal [Abstract]
CDARS	$ 5,011	$ 7,661
ICS	56,681	44,123
DDM	41,636	22,687
Total network deposits	103,328	74,471
One Way [Abstract]
CDARS	7,453	10,428
ICS	27,220	4,808
DDM	0	0
Total network deposits	$ 34,673	$ 15,236

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