XML 45 R35.htm IDEA: XBRL DOCUMENT v3.21.1

Investment Securities - Narrative (Details) - security	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Number of investment securities in unrealized loss position	29	10
Number of investment securities in unrealized loss position longer than 12 months	5
Number of investment securities in unrealized loss position less than 12 months	24

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

- References

No definition available.

+ Details

Name:	us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration