XML 10 R1.htm IDEA: XBRL DOCUMENT v3.23.3
Cover Page - shares
9 Months Ended
Sep. 30, 2023
Oct. 20, 2023
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2023  
Document Transition Report false  
Entity File Number 001-34095  
Entity Registrant Name FIRST BUSINESS FINANCIAL SERVICES, INC.  
Entity Incorporation, State or Country Code WI  
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  
Title of 12(b) Security Common Stock, $0.01 par value  
Trading Symbol FBIZ  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   8,314,901
Entity Central Index Key 0001521951  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2023  
Document Fiscal Period Focus Q3  
Amendment Flag false