XML 124 R109.htm IDEA: XBRL DOCUMENT
v3.20.4

Note 17 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale, Total | $ 387,347,000 | $ 334,655,000
Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
US Government Agencies Debt Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 242,141,000 | 186,410,000
Collateralized Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 24,890,000 | 42,470,000
Municipal General Obligation Bonds [Member] |  |
Debt Securities, Available-for-sale, Total | 107,824,000 | 101,079,000
Municipal Revenue Bonds [Member] |  |
Debt Securities, Available-for-sale, Total | 11,992,000 | 4,196,000
Other Debt and Equity Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 500,000 | 500,000
Fair Value, Recurring [Member] |  |
Debt Securities, Available-for-sale, Total | 387,347,000 | 334,655,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 386,581,000 | 332,605,000
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | 766,000 | 2,050,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 242,141,000 | 186,410,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 242,141,000 | 186,410,000
Fair Value, Recurring [Member] | US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 24,890,000 | 42,470,000
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 24,890,000 | 42,470,000
Fair Value, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] |  |
Debt Securities, Available-for-sale, Total | 107,824,000 | 101,079,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 107,058,000 | 99,029,000
Fair Value, Recurring [Member] | Municipal General Obligation Bonds [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | 766,000 | 2,050,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] |  |
Debt Securities, Available-for-sale, Total | 11,992,000 | 4,196,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 11,992,000 | 4,196,000
Fair Value, Recurring [Member] | Municipal Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] |  |
Debt Securities, Available-for-sale, Total | 500,000 | 500,000
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Debt Securities, Available-for-sale, Total | 0 | 0
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Debt Securities, Available-for-sale, Total | 500,000 | 500,000
Fair Value, Recurring [Member] | Other Debt and Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Debt Securities, Available-for-sale, Total | $ 0 | $ 0

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=mbwm_MunicipalGeneralObligationBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=mbwm_MunicipalRevenueBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=mbwm_OtherDebtAndEquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |