Document and Entity Information	3 Months Ended
	Mar. 31, 2013	May 09, 2013
Document and Entity Information [Abstract]
Entity Registrant Name	MERCANTILE BANK CORPORATION
Entity Central Index Key	0001042729
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Amendment Flag	false
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		8,705,412