XML 15 R1.htm IDEA: XBRL DOCUMENT v3.20.4
Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Feb. 22, 2021
Cover [Abstract]    
Document Type 10-K  
Document Annual Report true  
Document Period End Date Dec. 31, 2020  
Document Transition Report false  
Entity File Number 001-34095  
Entity Registrant Name FIRST BUSINESS FINANCIAL SERVICES, INC.  
Entity Central Index Key 0001521951  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus FY  
Amendment Flag false  
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 Well-known Seasoned Issuer No  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
ICFR Auditor Attestation Flag true  
Entity Shell Company false  
Entity Public Float $ 140.3  
Entity Common Stock, Shares Outstanding   8,511,536
Documents Incorporated by Reference Part III – Portions of the Proxy Statement for the Annual Meeting of Shareholders to be held on April 30, 2021 are incorporated by reference into Part III hereof.