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Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) (USD $) | 3 Months Ended |
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Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | $ 15,099,000 us-gaap_LoansAndLeasesReceivableAllowance |  | $ 14,224,000 us-gaap_LoansAndLeasesReceivableAllowance |  |
Provision for loan losses | 0 us-gaap_ProvisionForLoanAndLeaseLosses |  | 150,000 us-gaap_ProvisionForLoanAndLeaseLosses |  |
Charge-offs | (8,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs |  | (261,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs |  |
Recoveries | 65,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts |  | 119,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts |  |
Ending balance | 15,156,000 us-gaap_LoansAndLeasesReceivableAllowance |  | 14,232,000 us-gaap_LoansAndLeasesReceivableAllowance |  |
Ending ALLL related to loans collectively evaluated for impairment | 14,195,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment |  |  | 13,961,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment |
Ending ALLL related to loans individually evaluated for impairment | 954,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 |  |  | 1,131,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 |
Collectively evaluated for impairment | 1,317,883,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment |  |  | 1,334,638,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment |
Individually evaluated for impairment | 23,529,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | [1] |  | 23,521,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment | [2]
Total loans | 1,346,484,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [3] |  | 1,363,351,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [3]
Ratio of allowance for loan losses to total loans | 1.13%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans |  |  | 1.11%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans |
Allowance for loan losses to non-accrual loans | 160.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans |  |  | 161.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans |
PCI loans impaired post-acquisition | 1,600,000 bmrc_CertainLoansAndDebtSecuritiesAcquiredInTransferNetOfRelatedAllowanceForCreditLossesDueToSubsequentImpairment |  |  | 1,700,000 bmrc_CertainLoansAndDebtSecuritiesAcquiredInTransferNetOfRelatedAllowanceForCreditLossesDueToSubsequentImpairment |
Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 7,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 7,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 5,072,000 us-gaap_NotesReceivableNet / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 5,192,000 us-gaap_NotesReceivableNet / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Commercial and industrial |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 2,837,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 3,056,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |
Provision for loan losses | (275,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | (255,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |
Charge-offs | (2,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | (61,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |
Recoveries | 60,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 32,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |
Ending balance | 2,620,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  | 2,772,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 1,968,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |  | 2,143,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Ending ALLL related to loans individually evaluated for impairment | 648,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |  | 690,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Collectively evaluated for impairment | 192,557,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |  | 206,603,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Individually evaluated for impairment | 3,683,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [1] |  | 3,296,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [2]
Total loans | 196,442,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [3] |  | 210,223,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember | [3]
Ratio of allowance for loan losses to total loans | 1.33%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |  | 1.35%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |
Allowance for loan losses to non-accrual loans | 702.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember |  |  |  |
Commercial and industrial | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 4,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 4,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 202,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 324,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialLoanMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Commercial real estate, owner-occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 1,924,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 2,012,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |
Provision for loan losses | 170,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | (27,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |
Recoveries | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |
Ending balance | 2,094,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  | 1,985,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 2,062,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |  | 1,859,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Ending ALLL related to loans individually evaluated for impairment | 32,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |  | 65,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Collectively evaluated for impairment | 225,684,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |  | 220,933,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Individually evaluated for impairment | 7,024,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [1] |  | 7,056,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [2]
Total loans | 235,337,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [3] |  | 230,605,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember | [3]
Ratio of allowance for loan losses to total loans | 0.89%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |  | 0.83%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Allowance for loan losses to non-accrual loans | 149.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |  |  | 137.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember |
Commercial real estate, owner-occupied | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 2,629,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 2,616,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Commercial real estate, investor |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 6,672,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 6,196,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |
Provision for loan losses | (383,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 268,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |
Recoveries | 3,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 5,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |
Ending balance | 6,292,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  | 6,469,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 6,292,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |  | 6,672,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Ending ALLL related to loans individually evaluated for impairment | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Collectively evaluated for impairment | 648,809,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |  | 668,371,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Individually evaluated for impairment | 2,875,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [1] |  | 2,954,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [2]
Total loans | 653,848,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [3] |  | 673,499,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember | [3]
Ratio of allowance for loan losses to total loans | 0.96%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |  | 0.99%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Allowance for loan losses to non-accrual loans | 267.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |  |  | 275.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember |
Commercial real estate, investor | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 2,164,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 2,174,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_CommercialRealEstateInvestorFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Construction |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 839,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 633,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |
Provision for loan losses | (61,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 100,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | (197,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |
Recoveries | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |
Ending balance | 778,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  | 536,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 775,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |  | 836,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Ending ALLL related to loans individually evaluated for impairment | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Collectively evaluated for impairment | 51,383,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |  | 42,718,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Individually evaluated for impairment | 5,657,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [1] |  | 5,684,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [2]
Total loans | 57,050,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [3] |  | 48,413,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember | [3]
Ratio of allowance for loan losses to total loans | 1.36%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |  | 1.73%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Allowance for loan losses to non-accrual loans | 15.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |  |  | 16.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember |
Construction | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 3,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 3,000 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 10,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 11,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConstructionLoansMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Home equity |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 859,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 875,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |
Provision for loan losses | 63,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 11,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |
Recoveries | 1,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 1,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |
Ending balance | 923,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  | 887,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 922,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |  | 859,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Ending ALLL related to loans individually evaluated for impairment | 1,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Collectively evaluated for impairment | 112,649,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |  | 110,028,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Individually evaluated for impairment | 561,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [1] |  | 693,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [2]
Total loans | 113,277,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [3] |  | 110,788,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember | [3]
Ratio of allowance for loan losses to total loans | 0.81%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |  | 0.78%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Allowance for loan losses to non-accrual loans | 556.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |  |  | 307.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember |
Home equity | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 67,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 67,000 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_HomeEquityMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Other residential |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 433,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  | 317,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |
Provision for loan losses | (3,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  | 92,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |
Recoveries | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |
Ending balance | 430,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  | 409,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 345,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |  | 341,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |
Ending ALLL related to loans individually evaluated for impairment | 85,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |  | 92,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |
Collectively evaluated for impairment | 71,339,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |  | 70,990,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |
Individually evaluated for impairment | 2,036,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [1] |  | 2,045,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [2]
Total loans | 73,375,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3],[4] |  | 73,035,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember | [3],[4]
Ratio of allowance for loan losses to total loans | 0.59%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |  |  | 0.59%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember |
Other residential | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = bmrc_OtherResidentialFinancingReceivableMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Installment and other consumer |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 566,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 629,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Provision for loan losses | (99,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | (142,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Charge-offs | (6,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | (3,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Recoveries | 1,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 81,000 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Ending balance | 462,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  | 565,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 274,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |  | 282,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Ending ALLL related to loans individually evaluated for impairment | 188,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |  | 284,000 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Collectively evaluated for impairment | 15,462,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |  | 14,995,000 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Individually evaluated for impairment | 1,693,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [1] |  | 1,793,000 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [2]
Total loans | 17,155,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [3] |  | 16,788,000 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | [3]
Ratio of allowance for loan losses to total loans | 2.69%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |  | 3.37%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToTotalLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Allowance for loan losses to non-accrual loans | 585.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |  | 544.00%bmrc_LoansAndLeasesReceivableRatioOfAllowanceForLoanLossesToNonAccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |
Installment and other consumer | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Unallocated |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Beginning balance | 969,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  | 506,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Provision for loan losses | 588,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  | 103,000 us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Charge-offs | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Recoveries | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  | 0 us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Ending balance | 1,557,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  | 609,000 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Ending ALLL related to loans collectively evaluated for impairment | 1,557,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |  | 969,000 us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |
Ending ALLL related to loans individually evaluated for impairment | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |
Collectively evaluated for impairment | 0 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |  | 0 us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |
Individually evaluated for impairment | 0 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | [1] |  | 0 us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | [2]
Total loans | 0 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |  | 0 us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |
Unallocated | Receivables Acquired with Deteriorated Credit Quality |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Ending ALLL related to purchased credit-impaired loans | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | 0 us-gaap_FinancingReceivableAllowanceForCreditLosses / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
Purchase credit-impaired | $ 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |  |  | $ 0 us-gaap_NotesReceivableNet / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember / us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis = us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember |
[1] | Total excludes $1.6 million of PCI loans that have experienced post-acquisition declines in cash flows expected to be collected. These loans are included in the "purchased credit-impaired" amount in the next line below.
[2] | Total excludes $1.7 million PCI loans that have experienced credit deterioration post-acquisition, which are included in the "purchased credit-impaired" amount in the next line below.
[3] | 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.
[4] | 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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