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

For receivables acquired in a business combination, including certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

No definition available.

+ Details

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

- Definition

For receivables acquired in a business combination, including certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the future interest not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

No definition available.

+ Details

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

- Definition

Amount of expense to write-down the amortized cost basis of loans, before acquisition, to fair value. Expressed as a component of nonaccretable difference.

+ References

No definition available.

+ Details

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

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the unaccreted discount.

+ References

No definition available.

+ Details

Name:	mbwm_BusinessCombinationAcquiredReceivablesUnaccredtedDiscount
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of banking branches acquired in a business combination.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ 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

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ 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 (b)(2)
-URI http://asc.fasb.org/extlink&oid=56956791&loc=d3e4845-128472

+ Details

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

- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e1043-128460

+ Details

Name:	us-gaap_BusinessCombinationAcquisitionRelatedCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 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

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=mbwm_FirstbankCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 2 - Business Combination (Details)		12 Months Ended
Note 2 - Business Combination (Details)	Jun. 01, 2014 USD ($) shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Note 2 - Business Combination (Details) [Line Items]
Goodwill		$ 49,473,000	$ 49,473,000
Business Combination, Acquisition Related Costs		0	5,447,000	$ 1,246,000
Firstbank Corporation [Member]
Note 2 - Business Combination (Details) [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 1,452,880,000	$ 1,500,000,000
Business Combination, Branches Acquired	46	46
Business Acquisition, Conversion of Stock Per Share (in Shares) \| shares	1
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in Shares) \| shares	8,087,272
Goodwill	$ 49,473,000
Business Combination, Acquisition Related Costs			$ 5,400,000	$ 1,200,000
Business Combination, Acquired Receivables and Certain Loans, Estimated Uncollectible Cash Flows	10,400,000
Business Combination Acquired Receivables And Certain Loans Preacquisition Charge-offs	2,800,000
Business Combination Acquired Receivables And Certain Loans Estimated UncollectibleI nterest	3,900,000
Business Combination, Acquired Receivables, Gross Contractual Amount	926,400,000
Business Combination, Acquired Receivables, Unaccredted Discount	$ 8,100,000