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Document and Entity Information - shares
 9 Months Ended
Sep. 30, 2015
Oct. 27, 2015
Document and Entity Information [Abstract]    
Entity Registrant Name First Business Financial Services, Inc.  
Entity Central Index Key 0001521951  
Current Fiscal Year End Date --12-31  
Document Type 10-Q  
Document Period End Date Sep. 30, 2015  
Document Fiscal Year Focus 2015  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   8,697,089