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Note 8 - Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Disclosure Text Block [Abstract]
Time Deposits, More Than $250,000	$ 180.4	$ 223.0

X

- Definition

Amount of time deposit liabilities, including certificates of deposit, in denominations of $250,000 or more.

+ References

No definition available.

+ Details

Name:	mbwm_TimeDepositsMoreThan250000
Namespace Prefix:	mbwm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_DisclosureTextBlockAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration