Deposits (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Deposits (Textual) [Abstract]
Out-of-area certificates of deposit obtained through deposit brokers	$ 242.8
Out-of-area certificates of deposit obtained directly from depositors	$ 5.0

Out -of-area certificates of deposit obtained directly from depositors.

No definition available.

Name:	mbwm_OutOfAreaCertificatesOfDepositObtainedDirectlyFromDepositors
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration