XML 131 R117.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Note 21 - Regulatory Matters (Details Textual) - USD ($) |  |  |  |  |  |  |  |  |  |  |  | 9 Months Ended | 12 Months Ended | 23 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 22, 2017 | Jan. 12, 2017 | Dec. 21, 2016 | Oct. 13, 2016 | Sep. 21, 2016 | Jul. 14, 2016 | Jun. 23, 2016 | Apr. 14, 2016 | Mar. 23, 2016 | Jan. 26, 2016 | Jan. 14, 2016 | Sep. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2016 | Jan. 01, 2019 | Apr. 19, 2016 | Jan. 30, 2015 | Feb. 29, 2012 | Dec. 31, 2009
Capital Conservation Buffer |  |  |  |  |  |  |  |  |  |  |  |  | 2.50% |  |  | 2.50% |  |  |  |  |
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval |  |  |  |  |  |  |  |  |  |  |  |  | $ 54,600,000 |  |  | $ 54,600,000 |  |  |  |  |
Common Stock, Dividends, Per Share, Declared |  |  |  | $ 0.17 |  | $ 0.17 |  | $ 0.16 |  |  | $ 0.16 |  |  |  |  |  |  |  |  |  |
Stock Repurchase Program, Authorized Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 20,000,000 |  |
Stock Repurchase Program Additional Authorized Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 15,000,000 |  |  |
Stock Repurchased During Period, Shares |  |  |  |  |  |  |  |  |  |  |  |  | 167,878 |  |  | 956,419 |  |  |  |  |
Stock Repurchased During Period, Value |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,700,000 |  |  | $ 19,500,000 |  |  |  |  |
Treasury Stock Acquired, Average Cost Per Share |  |  |  |  |  |  |  |  |  |  |  |  | $ 22.23 |  |  | $ 20.38 |  |  |  |  |
Trust Preferred Securities Included in Tier One Capital |  |  |  |  |  |  |  |  |  |  |  |  | $ 42,800,000 | $ 53,100,000 |  | $ 42,800,000 |  |  |  |  |
Maximum Restricted Core Element Allowed in Tier One Capital Percent |  |  |  |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |
Maximum Level of Consolidated Aggregate Assets Allowing for Inclusion of Trust Preferred Securities in Tier OneC apital |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 15,000,000,000
Preferred Securities of Subsidiary Trust |  |  |  |  |  |  |  |  |  |  |  |  | 42,800,000 | 53,100,000 |  | 42,800,000 |  |  |  |  |
Payments for Repurchase of Trust Preferred Securities |  |  |  |  |  |  |  |  |  |  |  |  | 8,030,000 | 0 | $ 0 |  |  |  |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust |  |  |  |  |  |  |  |  |  |  |  |  | 44,835,000 | 55,154,000 |  | 44,835,000 |  |  |  | $ 32,000,000 |
Gain (Loss) on Repurchase of Trust Preferred Securities |  |  |  |  |  |  |  |  |  |  |  |  | 2,970,000 | $ 0 | $ 0 |  |  |  |  |  |
Increase (Decrease) in Tangible Equity to Tangible Assets Ratio Basis Point |  |  |  |  |  |  |  |  |  | 0.09% |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Tangible Book Value Per Share |  |  |  |  |  |  |  |  |  | $ 0.11 |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Tier One Capital and Total Risk Based Capital Ratio Basis Point |  |  |  |  |  |  |  |  |  | (0.35%) |  |  |  |  |  |  |  |  |  |  |
Dividends, Cash |  |  |  |  |  |  |  |  |  | $ 9,100,000 |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Capital Ratio Basis Point |  |  |  |  |  |  |  |  |  | (0.35%) |  |  |  |  |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Cash Paid |  |  |  |  | $ 0.17 |  | $ 0.16 |  | $ 0.16 |  |  |  |  |  |  |  |  |  |  |  |
Mercantile Bank Capital Trust I [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Securities of Subsidiary Trust |  |  |  |  |  |  |  |  |  | $ 32,000,000 |  |  | $ 21,000,000 |  |  | $ 21,000,000 |  |  |  |  |
Payments for Repurchase of Trust Preferred Securities |  |  |  |  |  |  |  |  |  | 11,000,000 |  |  |  |  |  |  |  |  |  |  |
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust |  |  |  |  |  |  |  |  |  | $ 21,000,000 |  |  |  |  |  |  |  |  |  |  |
Percentage of Trust Preferred Securities Face Amount Paid |  |  |  |  |  |  |  |  |  | 73.00% |  |  |  |  |  |  |  |  |  |  |
Discount Rate of Trust Preferred Securities |  |  |  |  |  |  |  |  |  | 27.00% |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Repurchase of Trust Preferred Securities |  |  |  |  |  |  |  |  |  | $ 1,800,000 |  |  |  |  |  |  |  |  |  |  |
Gain (Loss) on Repurchase of Trust Preferred Securities Per Diluted Share |  |  |  |  |  |  |  |  |  | $ 0.11 |  |  |  |  |  |  |  |  |  |  |
Fund [Member] | Mercantile Bank Capital Trust I [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Securities of Subsidiary Trust |  |  |  |  |  |  |  |  |  | $ 11,000,000 |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Declared |  | $ 0.18 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Special Dividends [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Declared |  |  |  | $ 0.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Cash Paid |  |  | $ 0.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Equity Tier 1 Risk Based Capital Required For Capital Adequacy to Risk Weighted Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.00% |  |  |  |
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.50% |  |  |  |
Capital Required for Capital Adequacy to Risk Weighted Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.50% |  |  |  |
Common Stock, Dividends, Per Share, Cash Paid | $ 0.18 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition An additional amount held in risk-based capital designed to ensure that banks build up capital buffers outside periods of stress which can be drawn down as losses are incurred. The requirement is based on simple capital conservation rules designed to avoid breaches of minimum capital requirements. + References No definition available. + Details
Name: | mbwm_CapitalConservationBuffer
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The minimum common equity tier one capital ratio (common equity tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References No definition available. + Details
Name: | mbwm_CommonEquityTier1RiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The discount rate of trust preferred securities that represents the percentage of the face amount are discounted. + References No definition available. + Details
Name: | mbwm_DiscountRateOfTrustPreferredSecurities
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of gain (loss), from the difference between the repurchase price of the trust preferred securities initially issued by the entity or its subsidiaries and the net carrying amount of the debt at the time of its repurchase. + References No definition available. + Details
Name: | mbwm_GainLossOnRepurchaseOfTrustPreferredSecurities
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the gain per diluted share on repurchase of trust preferred securities. + References No definition available. + Details
Name: | mbwm_GainLossOnRepurchaseOfTrustPreferredSecuritiesPerDilutedShare
Namespace Prefix: | mbwm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The base point increase or decrease in capital ratio. + References No definition available. + Details
Name: | mbwm_IncreaseDecreaseInCapitalRatioBasisPoint
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The increase or decrease in the company's tangible book value per share. + References No definition available. + Details
Name: | mbwm_IncreaseDecreaseInTangibleBookValuePerShare
Namespace Prefix: | mbwm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The basis point increase or decrease in our tangible equity to tangible assets ratio. + References No definition available. + Details
Name: | mbwm_IncreaseDecreaseInTangibleEquityToTangibleAssetsRatioBasisPoint
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The basis point increase or decrease in the company's regulatory tier 1 capital and total risk-based capital ratios. + References No definition available. + Details
Name: | mbwm_IncreaseDecreaseInTierOneCapitalAndTotalRiskBasedCapitalRatioBasisPoint
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maximum level of consolidated aggregate assets allowing for inclusion of trust preferred securities in Tier 1 Capital under the Dodd-Frank Act. + References No definition available. + Details
Name: | mbwm_MaximumLevelOfConsolidatedAggregateAssetsAllowingForInclusionOfTrustPreferredSecuritiesInTierOnecApital
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The maximum amount of restricted core elements allowed in tier one capital expressed as a percent. + References No definition available. + Details
Name: | mbwm_MaximumRestrictedCoreElementAllowedInTierOneCapitalPercent
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of trust preferred securities face amount to be paid. + References No definition available. + Details
Name: | mbwm_PercentageOfTrustPreferredSecuritiesFaceAmountPaid
Namespace Prefix: | mbwm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Trust preferred securities possesses characteristics of both equity and debt issues and are generally issued by bank holding companies. + References No definition available. + Details
Name: | mbwm_PreferredSecuritiesOfSubsidiaryTrust
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Additional amount of stock repurchase plan authorized. + References No definition available. + Details
Name: | mbwm_StockRepurchaseProgramAdditionalAuthorizedAmount
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Trust preferred securities held by the trust that are included in Tier One Capital and subject to certain limitations. + References No definition available. + Details
Name: | mbwm_TrustPreferredSecuritiesIncludedInTierOneCapital
Namespace Prefix: | mbwm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 + Details
Name: | us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
Name: | us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of paid and unpaid cash dividends declared for classes of stock, for example, but not limited to, common and preferred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 405 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817 + Details
Name: | us-gaap_DividendsCash
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash outflow to reacquire preferred stocks issued by a business trust or other special purpose entity, mainly established by a bank holding entity, to third party investors. The trust's assets are deeply subordinated debentures of the bank holding entity. Most trust preferred securities are subject to a mandatory redemption upon the repayment of the debentures. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3291-108585 + Details
Name: | us-gaap_PaymentsForRepurchaseOfTrustPreferredSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of dividends that can be declared or paid without approval of regulatory agency. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(e)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
Name: | us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 + Details
Name: | us-gaap_StockRepurchasedDuringPeriodShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_StockRepurchasedDuringPeriodValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826 + Details
Name: | us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
Name: | us-gaap_TreasuryStockAcquiredAverageCostPerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SubordinatedBorrowingAxis=mbwm_MercantileBankCapitalTrustIMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=mbwm_FundMember
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: |

X
- Details
Name: | us-gaap_DividendsAxis=mbwm_SpecialDividendsMember
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: |