Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2022	Apr. 29, 2022
Document Information [Line Items]
Entity Central Index Key	0001042729
Entity Registrant Name	MERCANTILE BANK CORPORATION
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2022
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2022
Document Transition Report	false
Entity File Number	000-26719
Entity Incorporation, State or Country Code	MI
Entity Tax Identification Number	38-3360865
Entity Address, Address Line One	310 Leonard Street, NW
Entity Address, City or Town	Grand Rapids
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	49504
City Area Code	616
Local Phone Number	406-3000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock
Trading Symbol	MBWM
Security Exchange Name	NASDAQ
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		15,843,442