    <SEC-DOCUMENT>0001521951-21-000096-index.html : 20211118
    <SEC-HEADER>0001521951-21-000096.hdr.sgml : 20211118
    <ACCEPTANCE-DATETIME>20211118164203
    ACCESSION NUMBER:		0001521951-21-000096
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		18
    CONFORMED PERIOD OF REPORT:	20211118
    ITEM INFORMATION:		Regulation FD Disclosure
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20211118
    DATE AS OF CHANGE:		20211118

    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:		211424953

    	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-20211118.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: fbiz-20211118.htm

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    <TYPE>EX-99.1
    <SEQUENCE>2
    <FILENAME>ceoreport-q32021finalfil.htm
    <DESCRIPTION>EX-99.1
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    Document 2 - file: ceoreport-q32021finalfil.htm

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    <SEQUENCE>3
    <FILENAME>fbiz-20211118.xsd
    <DESCRIPTION>XBRL TAXONOMY EXTENSION SCHEMA DOCUMENT
    <TEXT>
    Document 3 - file: fbiz-20211118.xsd

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    <SEQUENCE>4
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    <FILENAME>ceoreport-q32021finalfil005.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
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    <DOCUMENT>
    <TYPE>XML
    <SEQUENCE>11
    <FILENAME>fbiz-20211118_htm.xml
    <DESCRIPTION>IDEA: XBRL DOCUMENT
    <TEXT>
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    Document 11 - RAW XML: fbiz-20211118_htm.xml

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    <TYPE>XML
    <SEQUENCE>12
    <FILENAME>R1.htm
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    <TEXT>
    Document 12 - file: R1.htm

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    <TYPE>EXCEL
    <SEQUENCE>13
    <FILENAME>Financial_Report.xlsx
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    <SEQUENCE>14
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    <SEQUENCE>15
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    <TEXT>
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    <TYPE>XML
    <SEQUENCE>16
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    <TYPE>JSON
    <SEQUENCE>18
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    <TYPE>ZIP
    <SEQUENCE>19
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