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Deposits - Schedule of Stratification of Time Deposits (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
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Deposits [Abstract] |  |
Time deposits of less than or equal to $250 thousand | $ 134,068 | $ 145,697
Time deposits of more than $250 thousand | 108,309 | 105,620
Total time deposits | $ 242,377 | $ 251,317

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- Definition The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more. + References No definition available. + Details
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Namespace Prefix: | bmrc_
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Balance Type: | credit
Period Type: | instant

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- Definition Time Deposits, Less Than Or Equal To $250,000 + References No definition available. + Details
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Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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- Definition Amount of time deposit liabilities, including certificates of deposit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 405 -Topic 942 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478353/942-405-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 + Details
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