XML 42 R32.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Note 1 - Significant Accounting Policies (Details Textual) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 USD ($) shares | Jun. 30, 2017 shares | Jun. 30, 2018 USD ($) shares | Jun. 30, 2017 shares | Dec. 31, 2018 | Dec. 31, 2017 USD ($)
Number of Unconsolidated Business Trusts Formed to Issue Trust Preferred Securities | 5 |  | 5 |  |  |
Interest Income on Commercial and Mortgage Loans Discontinued Period |  |  | 90 days |  |  |
Maximum Delinquency Period for Consumer and Credit Card Loans to be Charged Off |  |  | 120 days |  |  |
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage | $ | $ 3.1 |  | $ 3.1 |  |  | $ 2.6
Servicing Asset, Total | $ | $ 610.0 |  | $ 610.0 |  |  |
Adjustments for New Accounting Principle, Early Adoption [Member] |  |  |  |  |  |
Reclassification from AOCI to Retained Earnings, Current Period | $ |  |  |  |  |  | $ 0.9
Scenario, Forecast [Member] |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent |  |  |  |  | 21.00% |
Core Deposits [Member] |  |  |  |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  |  | 10 years |  |  |
Restricted Stock [Member] |  |  |  |  |  |
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights | shares | 234,000 | 220,000 | 234,000 | 220,000 |  |
Employee Stock Option [Member] |  |  |  |  |  |
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights | shares | 17,000 | 34,000 | 17,000 | 34,000 |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares | 7,000 | 7,000 | 7,000 | 7,000 |  |

X
- Definition Number of days past due when interest income on commercial and mortgage loans is discontinued unless the loans are well-secured and in process of collection. + References No definition available. + Details
Name: | mbwm_InterestIncomeOnCommercialAndMortgageLoansDiscontinuedPeriod
Namespace Prefix: | mbwm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum number of days delinquent for consumer and credit card loans to be charged off. + References No definition available. + Details
Name: | mbwm_MaximumDelinquencyPeriodForConsumerAndCreditCardLoansToBeChargedOff
Namespace Prefix: | mbwm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of unconsolidated business trusts formed to issue trust preferred securities. + References No definition available. + Details
Name: | mbwm_NumberOfUnconsolidatedBusinessTrustsFormedToIssueTrustPreferredSecurities
Namespace Prefix: | mbwm_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of reclassification from AOCI to retained earnings during the current period. + References No definition available. + Details
Name: | mbwm_ReclassificationFromAOCIToRetainedEarningsCurrentPeriod
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
Name: | us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319 + Details
Name: | us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 61A -URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780137-109256 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 60B -URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780133-109256 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 68B -URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5498026-109256 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 59A -URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780131-109256 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 60A -URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780132-109256 + Details
Name: | us-gaap_IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after allowance for bad debt, of mortgage loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
Name: | us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroupMortgage
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745 + Details
Name: | us-gaap_ServicingAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AdjustmentsForNewAccountingPrincipleEarlyAdoptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |