XML 58 R43.htm IDEA: XBRL DOCUMENT
v3.20.4

Summary of Significant Accounting Policies - Financing Receivable Narrative (Details) | 12 Months Ended
--- | ---
Dec. 31, 2020 payment
Accounting Policies [Abstract] |
Threshold period a past due loan is charged off | 90 days
Number of consecutive payments considered sustained repayment performance | 6
Threshold period a past due overdraft account is charged off | 60 days

X
- Definition Loans and Leases Receivable, Nonperforming, Number Of Consecutive Payments Considered Sustained Repayment Performance + References No definition available. + Details
Name: | bmrc_LoansandLeasesReceivableNonperformingNumberOfConsecutivePaymentsConsideredSustainedRepaymentPerformance
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Threshold Period Past Due For Write-Off Of Deposit Liabilities Reclassified As Loans Receivable + References No definition available. + Details
Name: | bmrc_ThresholdPeriodPastDueForWriteOffOfDepositLiabilitiesReclassifiedAsLoansReceivable
Namespace Prefix: | bmrc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447 + Details
Name: | us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant