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Note 4 - Loans and Related Allowance for Loan Losses (Details) - Impaired Loans by Class (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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With no related allowance recorded: |  |
Recorded investment, with no related allowance | $ 10,119 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment | $ 9,284 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Unpaid principal balance, with no related allowance | 10,107 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance | 9,472 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
With an allowance recorded: |  |
Recorded investment, with related allowance | 4,249 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment | 9,681 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Unpaid principal balance, with related allowance | 4,246 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance | 9,720 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Related allowance | 1,596 us-gaap_ImpairedFinancingReceivableRelatedAllowance | 1,807 us-gaap_ImpairedFinancingReceivableRelatedAllowance
Total: |  |
Recorded investment | 14,368 us-gaap_ImpairedFinancingReceivableRecordedInvestment | 18,965 us-gaap_ImpairedFinancingReceivableRecordedInvestment
Unpaid principal balance | 14,353 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance | 19,192 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Related allowance | 1,596 us-gaap_ImpairedFinancingReceivableRelatedAllowance | 1,807 us-gaap_ImpairedFinancingReceivableRelatedAllowance
Commercial and Industrial [Member] |  |
With no related allowance recorded: |  |
Recorded investment, with no related allowance | 1,146 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 1,357 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Unpaid principal balance, with no related allowance | 1,145 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 1,357 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
With an allowance recorded: |  |
Recorded investment, with related allowance | 247 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 534 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Unpaid principal balance, with related allowance | 247 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 534 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Related allowance | 83 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 179 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Total: |  |
Recorded investment | 1,393 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 1,891 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Unpaid principal balance | 1,392 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 1,891 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Related allowance | 83 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember | 179 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialAndIndustrialMember
Real Estate Construction [Member] |  |
With no related allowance recorded: |  |
Recorded investment, with no related allowance | 2,707 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 124 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Unpaid principal balance, with no related allowance | 2,705 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 124 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
With an allowance recorded: |  |
Recorded investment, with related allowance | 589 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 3,887 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Unpaid principal balance, with related allowance | 589 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 3,887 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Related allowance | 589 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 210 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Total: |  |
Recorded investment | 3,296 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 4,011 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Unpaid principal balance | 3,294 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 4,011 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Related allowance | 589 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember | 210 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_RealEstateConstructionMember
Residential Real Estate Mortgage [Member] |  |
With no related allowance recorded: |  |
Recorded investment, with no related allowance | 2,202 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 2,704 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Unpaid principal balance, with no related allowance | 2,197 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 2,892 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
With an allowance recorded: |  |
Recorded investment, with related allowance | 2,981 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 3,178 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Unpaid principal balance, with related allowance | 2,978 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 3,217 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Related allowance | 892 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 855 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Total: |  |
Recorded investment | 5,183 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 5,882 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Unpaid principal balance | 5,175 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 6,109 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Related allowance | 892 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember | 855 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ResidentialRealEstateMortgageMember
Commercial Real Estate Mortgage [Member] |  |
With no related allowance recorded: |  |
Recorded investment, with no related allowance | 4,064 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 5,093 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Unpaid principal balance, with no related allowance | 4,060 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 5,093 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
With an allowance recorded: |  |
Recorded investment, with related allowance | 426 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 2,082 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Unpaid principal balance, with related allowance | 426 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 2,082 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Related allowance | 30 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 563 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Total: |  |
Recorded investment | 4,490 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 7,175 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Unpaid principal balance | 4,486 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 7,175 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Related allowance | 30 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember | 563 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_CommercialRealEstateMortgageMember
Consumer Installment [Member] |  |
With no related allowance recorded: |  |
Recorded investment, with no related allowance |  | 6 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember
Unpaid principal balance, with no related allowance |  | 6 us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember
With an allowance recorded: |  |
Recorded investment, with related allowance | 6 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember |
Unpaid principal balance, with related allowance | 6 us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember |
Related allowance | 2 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember |
Total: |  |
Recorded investment | 6 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember | 6 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember
Unpaid principal balance | 6 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember | 6 us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember
Related allowance | $ 2 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = mbcn_ConsumerInstallmentMember |

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- Definition Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 14A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524 + Details
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