Name:	mbwm_FederalHomeLoanBankAdvanceMaturityAfterYearFour
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480876/942-470-45-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 10
-Topic 470
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481544/470-10-50-1

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromOneToTwoYearsOfBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromThreeToFourYearsOfBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueFromTwoToThreeYearsOfBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in remainder of current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

No definition available.

Name:	us-gaap_FederalHomeLoanBankAdvancesMaturitiesSummaryDueInRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of advance from Federal Home Loan Bank (FHLBank) maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).