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Cover Page Cover Page
Sep. 09, 2021
Aug. 04, 2021
Cover [Abstract]    
Document Type 8-K  
Document Period End Date Sep. 09, 2021  
Entity Registrant Name First Business Financial Services, Inc.  
Entity Incorporation, State or Country Code WI  
Entity File Number 1-34095  
Entity Tax Identification Number 39-1576570  
Entity Address, Address Line One 401 Charmany Drive  
Entity Address, City or Town Madison  
Entity Address, State or Province WI  
Entity Address, Postal Zip Code 53719  
City Area Code 608  
Local Phone Number 238-8008  
Written Communications false  
Soliciting Material false  
Pre-commencement Tender Offer false  
Pre-commencement Issuer Tender Offer false  
Entity Emerging Growth Company false  
Title of 12(b) Security Common Stock, $0.01 par value  
Trading Symbol FBIZ  
Security Exchange Name NASDAQ  
Entity Central Index Key   0001521951
Amendment Flag   false