v3.19.2
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 26, 2019
Document and Entity Information [Abstract]    
Entity Current Reporting Status Yes  
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2019  
Entity Registrant Name BankFinancial CORP  
Entity Central Index Key 0001303942  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Emerging Growth Company false  
Entity Small Business true  
Entity Common Stock, Shares Outstanding   15,373,964
Entity Shell Company false