XML 63 R50.htm IDEA: XBRL DOCUMENT
v3.19.1

Investment Securities - Non-marketable Securities (Details) |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Nov. 27, 2018 | Oct. 31, 2018 USD ($) shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) shares | Feb. 21, 2019
Marketable Securities [Line Items] |  |  |  |  |
Federal Home Loan Bank stock, par value (usd per share) | $ / shares |  |  | $ 100 |  |
Stock split ratio | 2 |  |  |  |
Investments in low income housing tax credit funds |  |  | $ 4,600,000 | $ 2,100,000 |
Low income housing tax credits and other tax benefits |  |  | 597,000 |  |
Low income housing amortization expense |  |  | 507,000 |  |
Unfunded commitments for low income housing tax credit funds |  |  | 3,100,000 |  |
Catch-up amortization expense due to tax reduction |  |  |  | 67,000 |
Other assets |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Federal Home Loan Bank stock |  |  | $ 11,100,000 | $ 11,100,000 |
Visa Inc. Class B Common Stock |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Number of shares of securities carried at cost (in shares) | shares |  |  | 10,439 | 16,939 |
Fair value of Class B common stock |  |  | $ 0 |  |
Equity securities |  |  | $ 2,200,000 | $ 3,200,000 |
Shares of Visa Inc. Class B restricted common stock (in shares) | shares |  | 6,500 |  |  |
Gain from sale of Visa Inc. Class B restricted common stock |  | $ 956,000 |  |  |
Visa Inc. | Visa Inc. Class B common stock |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Stock split ratio |  |  | 1.6298 | 1.6483 |
Subsequent event |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Federal Home Loan Bank, dividend rate percentage |  |  |  |  | 7.00%

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 Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Amount + References No definition available. + Details
Name: | bmrc_EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActOf2017Amount
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Equity Securities FV NI, Number Of Shares Sold + References No definition available. + Details
Name: | bmrc_EquitySecuritiesFVNINumberOfSharesSold
Namespace Prefix: | bmrc_
Data Type: | xbrli:sharesItemType
Balance Type: | na
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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 740 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=114775393&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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 740 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=114775393&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 of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
Name: | us-gaap_EquitySecuritiesFvNi
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value. + References No definition available. + Details
Name: | us-gaap_EquitySecuritiesFvNiCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714 + Details
Name: | us-gaap_EquitySecuritiesFvNiRealizedGain
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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://fasb.org/us-gaap/role/ref/legacyRef -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 4: http://fasb.org/us-gaap/role/ref/legacyRef -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
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_MarketableSecuritiesLineItems
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://fasb.org/us-gaap/role/ref/legacyRef -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: | us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
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: |