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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
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans past due $ 10,431,000us-gaap_FinancingReceivableRecordedInvestmentPastDue $ 10,359,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
Current 1,336,053,000us-gaap_FinancingReceivableRecordedInvestmentCurrent 1,352,992,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
Total loans 1,346,484,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome [1] 1,363,351,000us-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 1,400,000bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceNonaccrualStatus 1,400,000bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceNonaccrualStatus
Purchased Credit-impaired (PCI) loans accreting interest 3,700,000bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceAccrualStatus 3,800,000bmrc_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalanceAccrualStatus
Number of accruing loans past due more than ninety days 0bmrc_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruingNumberOfLoans 0bmrc_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruingNumberOfLoans
Deferred loan fees 651,000us-gaap_LoansAndLeasesReceivableDeferredIncome 487,000us-gaap_LoansAndLeasesReceivableDeferredIncome
Unaccreted purchase discounts on non-PCI loans 4,200,000bmrc_CertainLoansAcquiredInTransferWithoutEvidenceOfDeterioriatedCreditUnaccretedPurchaseDiscounts 4,400,000bmrc_CertainLoansAcquiredInTransferWithoutEvidenceOfDeterioriatedCreditUnaccretedPurchaseDiscounts
30-59 days past due    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans past due 653,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
1,009,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
60-89 days past due    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans past due 296,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 9,482,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 9,350,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2]
Commercial and industrial    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans past due 682,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
183,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Current 195,760,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
210,040,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Total loans 196,442,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
[1] 210,223,000us-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 13,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
183,000us-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 296,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 373,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 0us-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 1,403,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
1,403,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Current 233,934,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
229,202,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Total loans 235,337,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
[1] 230,605,000us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
0us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 1,403,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 1,403,000us-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 2,354,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
2,429,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
Current 651,494,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
671,070,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
Total loans 653,848,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
[1] 673,499,000us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
0us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 2,354,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 2,429,000us-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 5,107,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
5,134,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
Current 51,943,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
43,279,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
Total loans 57,050,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
[1] 48,413,000us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
0us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 5,107,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 5,134,000us-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 461,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
926,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Current 112,816,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
109,862,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Total loans 113,277,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
[1] 110,788,000us-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 295,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
646,000us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 166,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] 280,000us-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 161,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[3] 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[3]
Current 73,214,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[3] 73,035,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[3]
Total loans 73,375,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[1],[3] 73,035,000us-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 161,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
[3] 0us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
[3] 0us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2],[3] 0us-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 263,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
284,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Current 16,892,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
16,504,000us-gaap_FinancingReceivableRecordedInvestmentCurrent
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Total loans 17,155,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
[1] 16,788,000us-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 184,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables30To59DaysPastDueMember
180,000us-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 0us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivables60To89DaysPastDueMember
0us-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 $ 79,000us-gaap_FinancingReceivableRecordedInvestmentPastDue
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_FinancingReceivablesPeriodPastDueAxis
= us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
[2] $ 104,000us-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.