XML 74 R59.htm IDEA: XBRL DOCUMENT
v3.20.4

Loans and Allowance for Credit Losses - Concentrations of Credit Narrative (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Loans, at amortized cost | $ 2,088,556 | $ 1,843,286
Commercial real estate |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Percentage of loans by class to all loans | 61.00% | 68.00%
Commercial real estate | California |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Percentage of loans by class and geographic location | 85.00% | 84.00%
Loans secured by real estate |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Percentage of loans by class to all loans | 77.00% | 88.00%
Commercial and industrial | Commercial |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Loans, at amortized cost | $ 498,408 | $ 246,687
Commercial and industrial | Commercial | Small Business Administration Paycheck Protection Program |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Loans, at amortized cost | $ 291,600 |

X
- Definition Loans and Leases Receivable, Ratio of Class of Loans by Geographic Location of Property + References No definition available. + Details
Name: | bmrc_LoansAndLeasesReceivableRatioOfClassOfLoansByGeographicLocationOfProperty
Namespace Prefix: | bmrc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Loans and Leases Receivable, Ratio of Class to All Loans + References No definition available. + Details
Name: | bmrc_LoansAndLeasesReceivableRatioOfClassToAllLoans
Namespace Prefix: | bmrc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- 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_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, before allowance for credit loss, of financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 80 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448 + Details
Name: | us-gaap_NotesReceivableGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=stpr_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bmrc_CommercialAndIndustrialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnusualOrInfrequentItemAxis=bmrc_SmallBusinessAdministrationPaycheckProtectionProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |