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v3.19.1

Recently Adopted and Issued Accounting Standards (Details) - Accounting Standards Update 2016-02 $ in Millions | Jan. 01, 2019 USD ($)
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New Accounting Pronouncements or Change in Accounting Principle [Line Items] |
Operating lease and finance lease, right-of-use asset | $ 13.4
Operating lease and finance lease, liability | $ 15.4

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- Definition Operating Lease And Finance Lease, Liability + References No definition available. + Details
Name: | bmrc_OperatingLeaseAndFinanceLeaseLiability
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Operating Lease And Finance Lease, Right-Of-Use Asset + References No definition available. + Details
Name: | bmrc_OperatingLeaseAndFinanceLeaseRightOfUseAsset
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition 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. + References No definition available. + Details
Name: | us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |