Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 25, 2022	Jun. 30, 2021
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	FY
Document Fiscal Year Focus	2021
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
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
Title of 12(b) Security	Common Stock
Trading Symbol	MBWM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 466,000,000
Entity Common Stock, Shares Outstanding		15,841,400
Auditor Name	BDO USA, LLP
Auditor Location	Grand Rapids, Michigan
Auditor Firm ID	243
ICFR Auditor Attestation Flag	true