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CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($)
Statement of Stockholders' Equity [Abstract] |
Fractional shares issued in acquisition, payment | $ 14

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- Definition Stockholders' Equity, Shares Issued For Acquisition, Fractional Shares, Value + References No definition available. + Details
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Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration