XML 11 R39.htm IDEA: XBRL DOCUMENT v2.4.1.9
Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance $ 15,099,000us-gaap_LoansAndLeasesReceivableAllowance $ 14,224,000us-gaap_LoansAndLeasesReceivableAllowance  
Provision for loan losses 0us-gaap_ProvisionForLoanAndLeaseLosses 150,000us-gaap_ProvisionForLoanAndLeaseLosses  
Charge-offs (8,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs (261,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs  
Recoveries 65,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts 119,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts  
Ending balance 15,156,000us-gaap_LoansAndLeasesReceivableAllowance 14,232,000us-gaap_LoansAndLeasesReceivableAllowance  
Ending ALLL related to loans collectively evaluated for impairment 14,195,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment   13,961,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Ending ALLL related to loans individually evaluated for impairment 954,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1   1,131,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Collectively evaluated for impairment 1,317,883,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment   1,334,638,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Individually evaluated for impairment 23,529,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment [1]   23,521,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment [2]
Total loans 1,346,484,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome [3]   1,363,351,000us-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 1,600,000bmrc_CertainLoansAndDebtSecuritiesAcquiredInTransferNetOfRelatedAllowanceForCreditLossesDueToSubsequentImpairment   1,700,000bmrc_CertainLoansAndDebtSecuritiesAcquiredInTransferNetOfRelatedAllowanceForCreditLossesDueToSubsequentImpairment
Receivables Acquired with Deteriorated Credit Quality      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Ending ALLL related to purchased credit-impaired loans 7,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  7,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 5,072,000us-gaap_NotesReceivableNet
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  5,192,000us-gaap_NotesReceivableNet
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Commercial and industrial      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 2,837,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
3,056,000us-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 60,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
32,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
 
Ending balance 2,620,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
2,772,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
 
Ending ALLL related to loans collectively evaluated for impairment 1,968,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
  2,143,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Ending ALLL related to loans individually evaluated for impairment 648,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
  690,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Collectively evaluated for impairment 192,557,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
  206,603,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
Individually evaluated for impairment 3,683,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
[1]   3,296,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
[2]
Total loans 196,442,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
[3]   210,223,000us-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 4,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  4,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 202,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialLoanMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  324,000us-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 1,924,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
2,012,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
 
Provision for loan losses 170,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
(27,000)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
 
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
 
Ending balance 2,094,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
1,985,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
 
Ending ALLL related to loans collectively evaluated for impairment 2,062,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
  1,859,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Ending ALLL related to loans individually evaluated for impairment 32,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
  65,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Collectively evaluated for impairment 225,684,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
  220,933,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
Individually evaluated for impairment 7,024,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
[1]   7,056,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
[2]
Total loans 235,337,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
[3]   230,605,000us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 2,629,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateOwnerOccupiedFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  2,616,000us-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 6,672,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
6,196,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
 
Provision for loan losses (383,000)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
268,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
 
Recoveries 3,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
5,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
 
Ending balance 6,292,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
6,469,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
 
Ending ALLL related to loans collectively evaluated for impairment 6,292,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
  6,672,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
Ending ALLL related to loans individually evaluated for impairment 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
Collectively evaluated for impairment 648,809,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
  668,371,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
Individually evaluated for impairment 2,875,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
[1]   2,954,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
[2]
Total loans 653,848,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
[3]   673,499,000us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 2,164,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  2,174,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_CommercialRealEstateInvestorFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Construction      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 839,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
633,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
 
Provision for loan losses (61,000)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
100,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
(197,000)us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
 
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
 
Ending balance 778,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
536,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
 
Ending ALLL related to loans collectively evaluated for impairment 775,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
  836,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
Ending ALLL related to loans individually evaluated for impairment 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
Collectively evaluated for impairment 51,383,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
  42,718,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
Individually evaluated for impairment 5,657,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
[1]   5,684,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
[2]
Total loans 57,050,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
[3]   48,413,000us-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 3,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  3,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 10,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConstructionLoansMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  11,000us-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 859,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
875,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Provision for loan losses 63,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
11,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Recoveries 1,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Ending balance 923,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
887,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Ending ALLL related to loans collectively evaluated for impairment 922,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
  859,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Ending ALLL related to loans individually evaluated for impairment 1,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Collectively evaluated for impairment 112,649,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
  110,028,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Individually evaluated for impairment 561,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
[1]   693,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
[2]
Total loans 113,277,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
[3]   110,788,000us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 67,000us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  67,000us-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 433,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
317,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
 
Provision for loan losses (3,000)us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
92,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
 
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
 
Ending balance 430,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
409,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
 
Ending ALLL related to loans collectively evaluated for impairment 345,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
  341,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
Ending ALLL related to loans individually evaluated for impairment 85,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
  92,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
Collectively evaluated for impairment 71,339,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
  70,990,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
Individually evaluated for impairment 2,036,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[1]   2,045,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[2]
Total loans 73,375,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
[3],[4]   73,035,000us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 0us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= bmrc_OtherResidentialFinancingReceivableMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-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 566,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
629,000us-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 1,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
81,000us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Ending balance 462,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
565,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Ending ALLL related to loans collectively evaluated for impairment 274,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  282,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending ALLL related to loans individually evaluated for impairment 188,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  284,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Collectively evaluated for impairment 15,462,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  14,995,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Individually evaluated for impairment 1,693,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
[1]   1,793,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
[2]
Total loans 17,155,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
[3]   16,788,000us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired 0us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-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 969,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
506,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Provision for loan losses 588,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
103,000us-gaap_ProvisionForLoanAndLeaseLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Charge-offs 0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
0us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Recoveries 0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
0us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Ending balance 1,557,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
609,000us-gaap_LoansAndLeasesReceivableAllowance
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Ending ALLL related to loans collectively evaluated for impairment 1,557,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
  969,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Ending ALLL related to loans individually evaluated for impairment 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Collectively evaluated for impairment 0us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
  0us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Individually evaluated for impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
[1]   0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
[2]
Total loans 0us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
  0us-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 0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  0us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Purchase credit-impaired $ 0us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
/ us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis
= us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
  $ 0us-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.