XML 11 R1.htm IDEA: XBRL DOCUMENT v3.10.0.1
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