XML 45 R35.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Investment Securities - Unrealized Loss Positions (Details) $ in Thousands | Mar. 31, 2018 USD ($) security | Dec. 31, 2017 USD ($) security
--- | --- | ---
Investments, Debt and Equity Securities [Abstract] |  |
Number of investment securities other-than-temporarily impaired | security | 0 |
Number of investment securities in unrealized loss position | security | 258 | 198
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | $ 42,777 | $ 31,051
Greater than or equal to 12 continuous months | 82,475 | 60,669
Total Securities in a loss position | 125,252 | 91,720
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (1,076) | (205)
Greater than or equal to 12 continuous months | (2,410) | (414)
Held-to-maturity, Gross Unrealized Losses | (3,486) | (619)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 329,365 | 212,675
Available-for-sale, greater than 12 continuous months, Fair value | 43,001 | 40,478
Available-for-sale, Total Securities in a loss position, Fair Value | 372,366 | 253,153
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (6,339) | (1,465)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (1,889) | (927)
Available-for-sale, Total Securities in a loss position, Unrealized loss | (8,228) | (2,392)
Marketable Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Marketable securities, less than 12 continuous months, Fair value | 372,142 | 243,726
Marketable securities, greater than 12 continuous months, Fair value | 125,476 | 101,147
Marketable securities, Total Securities in a loss position, Fair value | 497,618 | 344,873
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Marketable securities, less than 12 continuous months, Unrealized loss | (7,415) | (1,670)
Marketable securities, greater than 12 continuous months, Unrealized loss | (4,299) | (1,341)
Marketable securities, Total Securities in a loss position, Unrealized loss | $ (11,714) | (3,011)
Number of investment securities in unrealized loss position longer than 12 months | security | 61 |
Number of investment securities in unrealized loss position less than 12 months | security | 197 |
Collateralized Mortgage Obligations [Member] |  |
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position less than 12 months | security | 43 |
MBS pass-through securities issued by FHLMC and FNMA |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 71,449 | 32,189
Available-for-sale, greater than 12 continuous months, Fair value | 18,895 | 15,325
Available-for-sale, Total Securities in a loss position, Fair Value | 90,344 | 47,514
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (1,314) | (121)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (594) | (302)
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (1,908) | (423)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position longer than 12 months | security | 21 |
Number of investment securities in unrealized loss position less than 12 months | security | 34 |
SBA-backed securities |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 24,816 | 11,028
Available-for-sale, greater than 12 continuous months, Fair value | 165 | 165
Available-for-sale, Total Securities in a loss position, Fair Value | 24,981 | 11,193
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (277) | (53)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (2) | (2)
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (279) | (55)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position longer than 12 months | security | 1 |
Number of investment securities in unrealized loss position less than 12 months | security | 7 |
CMOs issued by FNMA |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 28,289 | 26,401
Available-for-sale, greater than 12 continuous months, Fair value | 5,061 | 5,440
Available-for-sale, Total Securities in a loss position, Fair Value | 33,350 | 31,841
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (473) | (171)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (133) | (77)
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (606) | (248)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position longer than 12 months | security | 3 |
CMOs issued by FHLMC |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 107,801 | 69,276
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 107,801 | 69,276
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (2,693) | (628)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (2,693) | (628)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position longer than 12 months | security | 4 |
CMOs issued by GNMA |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 15,955 | 14,230
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 15,955 | 14,230
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (528) | (194)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | (528) | (194)
Debentures of government- sponsored agencies |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | 12,330 | 2,984
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 12,330 | 2,984
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (116) | (5)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (116) | (5)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position less than 12 months | security | 5 |
Privately issued CMOs |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 862 | 1,310
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 862 | 1,310
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (2) | (2)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (2) | (2)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position less than 12 months | security | 1 |
Obligations of state and political subdivisions |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 63,831 | 52,197
Available-for-sale, greater than 12 continuous months, Fair value | 18,880 | 19,548
Available-for-sale, Total Securities in a loss position, Fair Value | 82,711 | 71,745
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (920) | (288)
Available-for-sale, greater than 12 continuous months, Unrealized loss | (1,160) | (546)
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (2,080) | (834)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position longer than 12 months | security | 32 |
Number of investment securities in unrealized loss position less than 12 months | security | 101 |
Corporate bonds |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Available-for-sale, less than 12 continuous months, Fair value | $ 4,032 | 3,060
Available-for-sale, greater than 12 continuous months, Fair value | 0 | 0
Available-for-sale, Total Securities in a loss position, Fair Value | 4,032 | 3,060
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Available-for-sale, less than 12 continuous months, Unrealized loss | (16) | (3)
Available-for-sale, greater than 12 continuous months, Unrealized loss | 0 | 0
Available-for-sale, Total Securities in a loss position, Unrealized loss | $ (16) | (3)
Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Number of investment securities in unrealized loss position less than 12 months | security | 6 |
Obligations of state and political subdivisions |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | $ 3,636 | 3,648
Greater than or equal to 12 continuous months | 0 | 0
Total Securities in a loss position | 3,636 | 3,648
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (20) | (31)
Greater than or equal to 12 continuous months | 0 | 0
Held-to-maturity, Gross Unrealized Losses | (20) | (31)
MBS pass-through securities issued by FHLMC and FNMA |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 22,570 | 16,337
Greater than or equal to 12 continuous months | 69,808 | 46,845
Total Securities in a loss position | 92,378 | 63,182
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (611) | (143)
Greater than or equal to 12 continuous months | (1,888) | (371)
Held-to-maturity, Gross Unrealized Losses | (2,499) | (514)
CMOs issued by FHLMC |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] |  |
Less than 12 continuous months | 16,571 | 11,066
Greater than or equal to 12 continuous months | 12,667 | 13,824
Total Securities in a loss position | 29,238 | 24,890
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Less than 12 continuous months | (445) | (31)
Greater than or equal to 12 continuous months | (522) | (43)
Held-to-maturity, Gross Unrealized Losses | $ (967) | $ (74)

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value, Total + References No definition available. + Details
Name: | bmrc_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValueTotal
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value + References No definition available. + Details
Name: | bmrc_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value + References No definition available. + Details
Name: | bmrc_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss + References No definition available. + Details
Name: | bmrc_AvailableforsaleSecuritiesandHeldtomaturitySecuritiesContinuousUnrealizedLossPosition12MonthsorLongerAccumulatedLoss
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss + References No definition available. + Details
Name: | bmrc_AvailableforsaleSecuritiesandHeldtomaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Available-for-sale Securities and Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss + References No definition available. + Details
Name: | bmrc_AvailableforsaleSecuritiesandHeldtomaturitySecuritiesContinuousUnrealizedLossPositionLessthan12MonthsAccumulatedLoss
Namespace Prefix: | bmrc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Marketable Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract] + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract
Namespace Prefix: | bmrc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Marketable Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesContinuousUnrealizedLossPositionFairValueAbstract
Namespace Prefix: | bmrc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Marketable Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Marketable Securities In Unrealized Loss Positions, Qualitative Disclosure, Number Of Positions, Less Than 12 Months + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThan12Months
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Marketable Securities In Unrealized Loss Positions, Qualitative Disclosure, Number Of Positions, Longer Than 12 Months + References No definition available. + Details
Name: | bmrc_MarketableSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLongerThan12Months
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Other than Temporary Impairment Losses, Investments, Number of Positions + References No definition available. + Details
Name: | bmrc_OtherThanTemporaryImpairmentLossesInvestmentsNumberOfPositions
Namespace Prefix: | bmrc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity in a continuous loss position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=bmrc_SmallBusinessAdministrationSBABackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtSecurityAxis=us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |