XML 15 R33.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Investment Securities - Non-Marketable Securities (Details) (USD $) | 3 Months Ended | 0 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2015 | Jan. 28, 2015 | Dec. 31, 2014 | Apr. 29, 2015
Schedule of Cost-method Investments [Line Items] |  |  |  |
Federal Home Loan Bank stock, par value | $ 100 bmrc_FederalHomeLoanBankStockParValue |  |  |
Investments in low income housing tax credit funds | $ 2,800,000 us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments |  | $ 1,800,000 us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments |
Low income housing tax credits and other tax benefits | 72,000 bmrc_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsTaxCredits |  |  |
Low income housing amortization expense | 56,000 us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization |  |  |
Unfunded commitments for low income housing tax credit funds | 2,200,000 bmrc_AffordableHousingProgramUnfundedCommitments |  |  |
Visa Inc. | Visa Inc. Class A common stock |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |
Stockholders' Equity Note, Stock Split, Conversion Ratio |  | 4 us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 / dei_LegalEntityAxis = bmrc_VisaIncMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassAMember |  |
Visa Inc. | Visa Inc. Class B common stock |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |
Stockholders' Equity Note, Stock Split, Conversion Ratio | 1.6483 us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 / dei_LegalEntityAxis = bmrc_VisaIncMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonClassBMember |  |  |
Visa Inc. Class B common stock |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |
Number of shares of securities carried at cost | 16,939 us-gaap_InvestmentOwnedBalanceShares / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bmrc_VisaInc.ClassBCommonStockMember |  |  |
Carrying value of securities carried at cost | 0 us-gaap_CostMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bmrc_VisaInc.ClassBCommonStockMember |  |  |
Fair value of Class B common stock | 1,800,000 us-gaap_CostMethodInvestmentsFairValueDisclosure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bmrc_VisaInc.ClassBCommonStockMember |  | 1,800,000 us-gaap_CostMethodInvestmentsFairValueDisclosure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = bmrc_VisaInc.ClassBCommonStockMember |
Subsequent event |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |
Federal Home Loan Bank, dividend rate percentage |  |  |  | 7.67%bmrc_FederalHomeLoanBankDividendRatePercentage / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Other assets |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |
Federal Home Loan Bank stock | $ 8,200,000 us-gaap_FederalHomeLoanBankStock / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherAssetsMember |  | $ 8,200,000 us-gaap_FederalHomeLoanBankStock / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherAssetsMember |

X
- Definition Affordable Housing Program, Unfunded Commitments + References No definition available. + Details
Name: | bmrc_AffordableHousingProgramUnfundedCommitments
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amortization Method Qualified Affordable Housing Project Investments, Tax Credits + References No definition available. + Details
Name: | bmrc_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsTaxCredits
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Federal Home Loan Bank, Dividend Rate, Percentage + References No definition available. + Details
Name: | bmrc_FederalHomeLoanBankDividendRatePercentage
Namespace Prefix: | bmrc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Federal Home Loan Bank Stock, Par Value + References No definition available. + Details
Name: | bmrc_FederalHomeLoanBankStockParValue
Namespace Prefix: | bmrc_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of investment in qualified affordable housing projects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 740 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=49127445&loc=SL49122993-202985 + Details
Name: | us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of amortization expense of investment in qualified affordable housing projects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 740 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=49127445&loc=SL49122993-202985 + Details
Name: | us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=29638308&loc=d3e40346-111594 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6872867&loc=d3e40691-111596 + Details
Name: | us-gaap_CostMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value portion of investments accounted under the cost method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=29638263&loc=d3e39828-111592 + Details
Name: | us-gaap_CostMethodInvestmentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809 + Details
Name: | us-gaap_FederalHomeLoanBankStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Balance held at close of period in number of shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010 + Details
Name: | us-gaap_InvestmentOwnedBalanceShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfCostMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Stock Split -URI http://asc.fasb.org/extlink&oid=6525746 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB TOPIC 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 + Details
Name: | us-gaap_StockholdersEquityNoteStockSplitConversionRatio1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=bmrc_VisaIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bmrc_VisaInc.ClassBCommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |