Name:	bmrc_FinancingReceivableModificationsContractsModifiedDuringPeriodRecordedInvestment
Namespace Prefix:	bmrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Number of financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Amount, after troubled debt restructuring, of modified financing receivable.

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount, before troubled debt restructuring, of financing receivable to be modified.

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524