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CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	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