    <SEC-DOCUMENT>0001521951-21-000047-index.html : 20210504
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    <ACCEPTANCE-DATETIME>20210504160703
    ACCESSION NUMBER:		0001521951-21-000047
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		26
    CONFORMED PERIOD OF REPORT:	20210430
    ITEM INFORMATION:		Submission of Matters to a Vote of Security Holders
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20210504
    DATE AS OF CHANGE:		20210504

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			FIRST BUSINESS FINANCIAL SERVICES, INC.
    		CENTRAL INDEX KEY:			0001521951
    		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
    		IRS NUMBER:				391576570
    		STATE OF INCORPORATION:			WI
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	001-34095
    		FILM NUMBER:		21888439

    	BUSINESS ADDRESS:
    		STREET 1:		401 CHARMANY DRIVE
    		CITY:			MADISON
    		STATE:			WI
    		ZIP:			53719
    		BUSINESS PHONE:		608-238-8008

    	MAIL ADDRESS:
    		STREET 1:		401 CHARMANY DRIVE
    		STREET 2:		PO BOX 44961
    		CITY:			MADISON
    		STATE:			WI
    		ZIP:			53744

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	First Business Financial Services, Inc.
    		DATE OF NAME CHANGE:	20110527
    </SEC-HEADER>
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    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>fbiz-20210430.htm
    <DESCRIPTION>8-K
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    <SEQUENCE>2
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    <SEQUENCE>3
    <FILENAME>fbiz-20210430.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
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    <SEQUENCE>24
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    <TYPE>JSON
    <SEQUENCE>26
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