XML 11 R1.htm IDEA: XBRL DOCUMENT v3.19.2
Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2019
Jul. 31, 2019
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 Emerging Growth Company false  
Entity Small Business false  
Entity Common Stock, Shares Outstanding (in shares)   16,424,433
Entity Shell Company false  
Document Type 10-Q  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Title of 12(b) Security Common Stock