Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 30, 2017
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)		16,465,988
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Amendment Flag	false