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Recently Adopted and Issued Accounting Standards (Details) $ in Millions	Sep. 30, 2023 USD ($) contract
Accounting Policies [Abstract]
Number of interest rate swap contracts | contract	4
Derivative, notional amount | $	$ 11.3

X

- Definition

Number Of Interest Rate Swap Contract

+ References

No definition available.

+ Details

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Namespace Prefix:	bmrc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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X

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1A

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