XML 43 R33.htm IDEA: XBRL DOCUMENT
v3.21.2

Investment Securities - Schedule of Bond Ratings For Held-to-Maturity Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | $ 196,801 | $ 109,036
Obligations of state and political subdivisions |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 22,532 | 1,667
Moody's And/Or Standard & Poor's AAA Rating | Obligations of state and political subdivisions |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 7,455 | 0
Moody's And/Or Standard & Poor's AA Rating | Obligations of state and political subdivisions |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 14,975 | 1,461
Moody's And/Or Standard & Poor's A Rating | Obligations of state and political subdivisions |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | $ 102 | $ 206

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_DebtSecuritiesHeldToMaturityCreditQualityIndicatorLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity). + References No definition available. + Details
Name: | us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | bmrc_CreditRatingMoodysAndOrStandardPoorsAxis=bmrc_MoodysAndOrStandardPoorsAAARatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | bmrc_CreditRatingMoodysAndOrStandardPoorsAxis=bmrc_MoodysAndOrStandardPoorsAARatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | bmrc_CreditRatingMoodysAndOrStandardPoorsAxis=bmrc_MoodysAndOrStandardPoorsARatingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |