The number of shares that each share of the acquiree is converted into shares of the acquirer.

No definition available.

Name:	mbwm_BusinessAcquisitionConversionOfStockPerShare
Namespace Prefix:	mbwm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of banking branches acquired in a business combination.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbwm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of trusts for which debt assumed in a business combination are payable to.

+ References

No definition available.

+ Details

Name:	mbwm_BusinessCombinationDebtAssumedNumberOfTrusts
Namespace Prefix:	mbwm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	mbwm_Note2BusinessCombinationDetailsLineItems
Namespace Prefix:	mbwm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)(4)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of assets acquired at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

+ References

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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- Details

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- Details

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Note 2 - Business Combination (Details) (USD $)	0 Months Ended
Note 2 - Business Combination (Details) (USD $)	Jun. 01, 2014	Mar. 31, 2015	Dec. 31, 2014
Note 2 - Business Combination (Details) [Line Items]
Goodwill		$ 49,473,000us-gaap_Goodwill	$ 49,473,000us-gaap_Goodwill
Minimum [Member] \| Firstbank Corporation [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Acquired Trusts [Member]
Note 2 - Business Combination (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.27%
Maximum [Member] \| Firstbank Corporation [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Acquired Trusts [Member]
Note 2 - Business Combination (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.99%
Firstbank Corporation [Member]
Note 2 - Business Combination (Details) [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	1,500,000,000
Business Combination, Branches Acquired	46
Business Acquisition, Conversion of Stock Per Share (in Shares)	1
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in Shares)	8,087,272
Goodwill	49,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	36,100,000
Business Combination, Debt Assumed, Number of Trusts	4
Estimate of Fair Value Measurement [Member] \| Firstbank Corporation [Member]
Note 2 - Business Combination (Details) [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	21,100,000