XML 11 R1.htm IDEA: XBRL DOCUMENT v3.5.0.2
Document And Entity Information - shares
9 Months Ended
Sep. 30, 2016
Nov. 04, 2016
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)   16,302,213
Document Type 10-Q  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Amendment Flag false