Note 7 - Federal Home Loan Bank of Indianapolis Advances (Details Textual) - USD ($)	Jun. 30, 2022	Dec. 31, 2021
Long-Term Federal Home Loan Bank Advances, Total	$ 362,263,000	$ 374,000,000
Line of Credit Facility, Maximum Borrowing Capacity	932,000,000
Line of Credit Facility, Remaining Borrowing Capacity	564,000,000
Federal Home Loan Bank of Indianapolis [Member] \| Bullet Advances [member]
Long-Term Federal Home Loan Bank Advances, Total	$ 334,000,000	$ 374,000,000
Federal Home Loan Bank of Indianapolis [Member] \| Bullet Advances [member] \| Minimum [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End	0.55%	0.55%
Federal Home Loan Bank of Indianapolis [Member] \| Bullet Advances [member] \| Maximum [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End	3.18%	3.18%
Federal Home Loan Bank of Indianapolis [Member] \| Bullet Advances [member] \| Weighted Average [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End	1.96%	2.00%
Federal Home Loan Bank of Indianapolis [Member] \| Amortizing Advances [Member]
Long-Term Federal Home Loan Bank Advances, Total	$ 28,300,000	$ 0
Federal Home Loan Bank of Indianapolis [Member] \| Amortizing Advances [Member] \| Weighted Average [Member]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End	2.52%

States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=123599511&loc=d3e64702-112823

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfIndianapolisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mbwm_BulletAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mbwm_AmortizingAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: