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Loans and Allowance for Loan Losses - Loans Outstanding and Aging Analysis (Details) (USD $) | Mar. 31, 2015 loans | Dec. 31, 2014 loans
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Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | $ 10,431,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue |  | $ 10,359,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue |
Current | 1,336,053,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent |  | 1,352,992,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent |
Total loans | 1,346,484,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1] | 1,363,351,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1]
Non-accrual loans to total loans | 0.70%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans |  | 0.70%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans |
Purchased Credit Impaired (PCI) loans no longer accreting interest | 1,400,000 bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceNonaccrualStatus |  | 1,400,000 bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceNonaccrualStatus |
Purchased Credit-impaired (PCI) loans accreting interest | 3,700,000 bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceAccrualStatus |  | 3,800,000 bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceAccrualStatus |
Number of accruing loans past due more than ninety days | 0 bmrc_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruingNumberOfLoans |  | 0 bmrc_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruingNumberOfLoans |
Deferred loan fees | 651,000 us-gaap_LoansAndLeasesReceivableDeferredIncome |  | 487,000 us-gaap_LoansAndLeasesReceivableDeferredIncome |
Unaccreted purchase discounts on non-PCI loans | 4,200,000 bmrc_CertainLoansAcquiredInTransferWithoutEvidenceOfDeterioriatedCreditUnaccretedPurchaseDiscounts |  | 4,400,000 bmrc_CertainLoansAcquiredInTransferWithoutEvidenceOfDeterioriatedCreditUnaccretedPurchaseDiscounts |
30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 653,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 1,009,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 296,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 9,482,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 9,350,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Commercial and industrial |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 682,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 183,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Current | 195,760,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 210,040,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Total loans | 196,442,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [1] | 210,223,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [1]
Non-accrual loans to total loans | 0.20%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 0.00%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Commercial and industrial | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 13,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 183,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Commercial and industrial | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 296,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Commercial and industrial | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 373,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Commercial real estate, owner-occupied |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 1,403,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 1,403,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Current | 233,934,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 229,202,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Total loans | 235,337,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [1] | 230,605,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [1]
Non-accrual loans to total loans | 0.60%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 0.60%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Commercial real estate, owner-occupied | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Commercial real estate, owner-occupied | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Commercial real estate, owner-occupied | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 1,403,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 1,403,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Commercial real estate, investor |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 2,354,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 2,429,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Current | 651,494,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 671,070,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Total loans | 653,848,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [1] | 673,499,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [1]
Non-accrual loans to total loans | 0.40%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 0.40%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Commercial real estate, investor | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Commercial real estate, investor | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Commercial real estate, investor | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 2,354,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 2,429,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Construction |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 5,107,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 5,134,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Current | 51,943,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 43,279,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Total loans | 57,050,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [1] | 48,413,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [1]
Non-accrual loans to total loans | 9.00%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 10.60%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Construction | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Construction | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Construction | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 5,107,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 5,134,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Home equity |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 461,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 926,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Current | 112,816,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 109,862,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Total loans | 113,277,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [1] | 110,788,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [1]
Non-accrual loans to total loans | 0.10%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 0.30%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Home equity | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 295,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 646,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Home equity | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Home equity | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 166,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | 280,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
Other residential |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 161,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3] | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3]
Current | 73,214,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3] | 73,035,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3]
Total loans | 73,375,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [1],[3] | 73,035,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [1],[3]
Non-accrual loans to total loans | 0.00%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3] | 0.00%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3]
Other residential | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 161,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember | [3] | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember | [3]
Other residential | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember | [3] | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember | [3]
Other residential | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2],[3] | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2],[3]
Installment and other consumer |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 263,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 284,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Current | 16,892,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 16,504,000 us-gaap_FinancingReceivableRecordedInvestmentCurrent / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Total loans | 17,155,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [1] | 16,788,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [1]
Non-accrual loans to total loans | 0.50%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 0.60%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Installment and other consumer | 30-59 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 184,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |  | 180,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables30To59DaysPastDueMember |
Installment and other consumer | 60-89 days past due |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |  | 0 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivables60To89DaysPastDueMember |
Installment and other consumer | Greater than 90 days past due (non-accrual) 2 |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Loans past due | $ 79,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2] | $ 104,000 us-gaap_FinancingReceivableRecordedInvestmentPastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_FinancingReceivablesPeriodPastDueAxis = us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember | [2]
[1] | Amounts include net deferred loan costs of $651 thousand and $487 thousand at March 31, 2015 and December 31, 2014, respectively. Amounts are also net of unaccreted purchase discounts on non-PCI loans of $4.2 million and $4.4 million at March 31, 2015 and December 31, 2014, respectively.
[2] | Amounts include $1.4 million of Purchased Credit Impaired ("PCI") loans that have stopped accreting interest at both March 31, 2015 and December 31, 2014. Amounts exclude accreting PCI loans of $3.7 million and $3.8 million at March 31, 2015 and December 31, 2014, respectively, as we have a reasonable expectation about future cash flows to be collected and we continue to recognize accretable yield on these loans in interest income. There were no accruing loans past due more than ninety days at March 31, 2015 or December 31, 2014.
[3] | Our residential loan portfolio does not include sub-prime loans, nor is it our practice to underwrite loans commonly referred to as "Alt-A mortgages", the characteristics of which are loans lacking full documentation, borrowers having low FICO scores or higher loan-to-value ratios.

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