Note 10 - Fair Values of Financial Instruments (Details Textual)	Oct. 21, 2020
Hastings, Michigan Branch Office [Member] \| Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Deposit Accounts, Premium of Book Balance	5.00%

The premium of book balance of deposit accounts paid by the counter party in a disposal group transaction.

No definition available.

Name:	mbwm_DisposalGroupIncludingDiscontinuedOperationDepositAccountsPremiumOfBookBalance
Namespace Prefix:	mbwm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration