XML 42 R33.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Investment Securities - Narrative (Details) | 1 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2022 USD ($) | Sep. 30, 2022 USD ($) security | Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items] |  |  |
Held-to-maturity, allowance for credit Loss |  | $ 0 | $ 0
Transfer of securities from available-for-sale to held-to-maturity at fair value | $ 357,500,000 |  |
Net unrealized pre-tax loss |  | $ 98,990,000 | $ 13,026,000
Number of investment securities in unrealized loss position | security |  | 409 | 217
Number of investment securities in unrealized loss position longer than 12 months | security |  | 173 |
Number of investment securities in unrealized loss position less than 12 months | security |  | 236 |
Debt securities, available-for-sale unrealized loss position, allowance for credit loss |  | $ 0 |
Accumulated Other Comprehensive Income (Loss), Net of Tax |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Net unrealized pre-tax loss | $ 14,800,000 |  |

X
- Definition Debt Securities, Available-For-Sale Unrealized Loss Position, Allowance For Credit Loss + References No definition available. + Details
Name: | bmrc_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAllowanceForCreditLoss
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Marketable Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Marketable Securities In Unrealized Loss Positions, Qualitative Disclosure, Number Of Positions, Less Than 12 Months + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThan12Months
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Marketable Securities In Unrealized Loss Positions, Qualitative Disclosure, Number Of Positions, Longer Than 12 Months + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLongerThan12Months
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of credit loss expense on investment in debt security measured at amortized cost (held-to-maturity) transferred into held-to-maturity out of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8B -URI https://asc.fasb.org/extlink&oid=124260329&loc=SL120268709-111562 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleTransferToHeldToMaturityAllowanceForCreditLossExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
Name: | us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=bmrc_AccumulatedOtherComprehensiveIncomeLossNetOfTaxMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |