Business Combinations, Number of Debt Instruments Acquired

No definition available.

Name:	bmrc_BusinessCombinationsNumberofDebtInstrumentsAcquired
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- Definition

This element represents the disclosures for fair value estimates for financial instruments required in the footnote disclosures to the financial statements. Carrying amount reprsents accrued interest payable on all forms of debt, including deposit liabilities, that has been incurred and is unpaid for time value of money. The carrying value may approximate fair value due to the short-term nature of their settlement dates.

+ References

No definition available.

+ Details

Name:	bmrc_InterestPayableFairValueDisclosure
Namespace Prefix:	bmrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the disclosures for fair value estimates for financial instruments required in the footnote disclosures to the financial statements. Carrying amount reprsents interest earned but not received from loan borrowers, investment security issuers and on other forms of short-term investment for time value of money. The carrying value may approximate fair value due to the short-term nature of their settlement dates.

+ References

No definition available.

+ Details

Name:	bmrc_InterestReceivableFairValueDisclosure
Namespace Prefix:	bmrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

Name:	us-gaap_DepositsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

+ Details

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a),(b)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_FederalHomeLoanBankBorrowingsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_SubordinatedLongtermDebtCurrentAndNoncurrentAbstract
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Period Type:	duration

- Details

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- Details

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- Details

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Fair Value of Assets and Liabilities - Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	3 Months Ended
	Nov. 29, 2013	Mar. 31, 2015	Dec. 31, 2014
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		109,785	$ 118,643
Subordinated Debt [Abstract]
Number of subordinated debentures acquired	2
Fair value of loan commitments and standby letters of credit		811	1,000
Subordinated debenture
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Subordinated debentures	4,950
Subordinated Debt [Abstract]
Number of subordinated debentures acquired	2
NorCal Community Bancorp Trust I \| Subordinated debenture
Subordinated Debt [Abstract]
Basis spread on subordinated debentures	3.05%	3.05%
NorCal Community Bancorp Trust II \| Subordinated debenture
Subordinated Debt [Abstract]
Basis spread on subordinated debentures	1.40%	1.40%
Carrying Value \| Fair Value Hierarchy, Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents		103,164	41,367
Carrying Value \| Fair Value Hierarchy, Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		107,476	116,437
Interest receivable		5,453	5,909
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits		1,585,120	1,551,619
Federal Home Loan Bank borrowings		15,000	15,000
Interest payable		208	213
Carrying Value \| Fair Value Hierarchy, Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Loans, net		1,331,328	1,348,252
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Subordinated debentures		5,238	5,185
Fair Value \| Fair Value Hierarchy, Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents		103,164	41,367
Fair Value \| Fair Value Hierarchy, Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Investment securities held to maturity		109,785	118,643
Interest receivable		5,453	5,909
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits		1,585,907	1,552,446
Federal Home Loan Bank borrowings		15,514	15,484
Interest payable		208	213
Fair Value \| Fair Value Hierarchy, Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Loans, net		1,341,118	1,361,244
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Subordinated debentures		5,274	$ 5,290