XML 53 R43.htm IDEA: XBRL DOCUMENT
v3.21.2

Loans and Allowance for Credit Losses on Loans - Outstanding and Aging Analysis (Details) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2021 USD ($) loan | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | $ 2,317,019,000 |  | $ 2,088,556,000
Non-accrual loans with no allowance | 8,423,000 |  | 9,233,000
Loans past due more than 90 days still accruing | 0 |  | 0
Financing receivable, nonaccrual, earning interest on cash basis | 0 |  | 0
Financing receivable, nonaccrual, interest income | $ 0 | $ 0 |
Financing receivable, number of loans placed on nonaccrual status | loan | 0 |  |
Financing receivable, accrued interest, writeoff |  | $ 20,000 |
Commercial loans | Commercial and industrial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | $ 377,965,000 |  | 498,408,000
Non-accrual loans with no allowance | 0 |  | 0
Commercial real estate loans | American River Bank (ARB) |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 118,000 |  |
Commercial real estate loans | Commercial owner-occupied |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 398,543,000 |  | 304,963,000
Non-accrual loans with no allowance | 7,273,000 |  | 7,147,000
Commercial real estate loans | Commercial investor-owned |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,157,344,000 |  | 961,208,000
Non-accrual loans with no allowance | 709,000 |  | 1,610,000
Commercial real estate loans | Construction |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 125,060,000 |  | 73,046,000
Non-accrual loans with no allowance | 0 |  | 0
Residential loans | Home equity |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 92,396,000 |  | 104,813,000
Non-accrual loans with no allowance | 441,000 |  | 459,000
Residential loans | Other residential |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 117,778,000 |  | 123,395,000
Non-accrual loans with no allowance | 0 |  | 0
Consumer loans | Installment and other consumer loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 47,933,000 |  | 22,723,000
Non-accrual loans with no allowance | 0 |  | 17,000
Financial asset, other than financial asset acquired with credit deterioration |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 2,317,019,000 |  | 2,088,556,000
Non-accrual | 8,423,000 |  |
Financial asset, other than financial asset acquired with credit deterioration | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 397,000 |  | 2,083,000
Non-accrual |  |  | 9,233,000
Financial asset, other than financial asset acquired with credit deterioration | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,046,000 |  | 622,000
Financial asset, other than financial asset acquired with credit deterioration | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,443,000 |  | 2,705,000
Financial asset, other than financial asset acquired with credit deterioration | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 2,315,576,000 |  | 2,085,851,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 377,965,000 |  | 498,408,000
Non-accrual | 0 |  |
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 181,000 |  | 0
Non-accrual |  |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 924,000 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,105,000 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial loans | Commercial and industrial | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 376,860,000 |  | 498,408,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 398,543,000 |  | 304,963,000
Non-accrual | 7,273,000 |  |
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Non-accrual |  |  | 7,147,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial owner-occupied | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 398,543,000 |  | 304,963,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,157,344,000 |  | 961,208,000
Non-accrual | 709,000 |  |
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 1,673,000
Non-accrual |  |  | 1,610,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost |  |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 1,673,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Commercial investor-owned | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,157,344,000 |  | 959,535,000
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 125,060,000 |  | 73,046,000
Non-accrual | 0 |  |
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Non-accrual |  |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Commercial real estate loans | Construction | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 125,060,000 |  | 73,046,000
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 92,396,000 |  | 104,813,000
Non-accrual | 441,000 |  |
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 143,000 |  | 274,000
Non-accrual |  |  | 459,000
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 121,000 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 264,000 |  | 274,000
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Home equity | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 92,132,000 |  | 104,539,000
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 117,778,000 |  | 123,395,000
Non-accrual | 0 |  |
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Non-accrual |  |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Residential loans | Other residential | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 117,778,000 |  | 123,395,000
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 47,933,000 |  | 22,723,000
Non-accrual | 0 |  |
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans | 30-59 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 73,000 |  | 136,000
Non-accrual |  |  | 17,000
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans | 60-89 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 1,000 |  | 622,000
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans | 90 days or more past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 0 |  | 0
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans | Total past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | 74,000 |  | 758,000
Financial asset, other than financial asset acquired with credit deterioration | Consumer loans | Installment and other consumer loans | Current |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans at amortized cost | $ 47,859,000 |  | $ 21,965,000

X
- Definition Financing Receivable, Nonaccrual, Earning Interest On Cash Basis + References No definition available. + Details
Name: | bmrc_FinancingReceivableNonaccrualEarningInterestOnCashBasis
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Financing Receivable, Number Of Loans Placed On Nonaccrual Status + References No definition available. + Details
Name: | bmrc_FinancingReceivableNumberOfLoansPlacedOnNonaccrualStatus
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Amount of writeoff of accrued interest on financing receivable recognized by reversing interest income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3D -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267969-210447 + Details
Name: | us-gaap_FinancingReceivableAccruedInterestWriteoff
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount excluding accrued interest, before allowance for credit loss, of financing receivable. + References Reference 1: 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=124255953&loc=SL82919230-210447 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 + Details
Name: | us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of interest income on financing receivable on nonaccrual status. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 16 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447 + Details
Name: | us-gaap_FinancingReceivableNonaccrualInterestIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of financing receivable on nonaccrual status with no allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 16 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447 + Details
Name: | us-gaap_FinancingReceivableNonaccrualNoAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of financing receivable 90 days or more past due and still accruing. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 16 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524 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=124267575&loc=SL82922355-210448 + Details
Name: | us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of financing receivable on nonaccrual status. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 16 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (3) Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph (a) -Subparagraph (2) + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=bmrc_AmericanRiverBankARBMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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

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

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

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

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

X
- Details
Name: | us-gaap_CreditLossStatusAxis=us-gaap_FinancialAssetOtherThanFinancialAssetAcquiredWithCreditDeteriorationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables30To59DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables60To89DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetNotPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |