Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 06, 2018
Document Information [Line Items]
Entity Registrant Name	MERCANTILE BANK CORPORATION
Entity Central Index Key	0001042729
Trading Symbol	mbwm
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		16,610,434
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Amendment Flag	false