Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Nov. 06, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	MERCANTILE BANK CORPORATION
Trading Symbol	mbwm
Document Type	10-Q
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		16,265,996
Amendment Flag	false
Entity Central Index Key	0001042729
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Well-known Seasoned Issuer	No
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3