<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xml:lang="en-US"
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2022"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="fbiz-20230428.xsd" xlink:type="simple"/>
    <context id="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001521951</identifier>
        </entity>
        <period>
            <startDate>2023-04-28</startDate>
            <endDate>2023-04-28</endDate>
        </period>
    </context>
    <dei:EntityCentralIndexKey
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV80L2ZyYWc6NGE2Mjc1YTRhNzA2NDgzOWIyZjEwZDJiMTcwYjEzZTAvdGFibGU6MGQyZjlkOTRkMTlmNDg3NGFjYzA2NzA0YzU5YTFmOTUvdGFibGVyYW5nZTowZDJmOWQ5NGQxOWY0ODc0YWNjMDY3MDRjNTlhMWY5NV8yLTEtMS0xLTE3NDIwMQ_b9f43a17-44a9-4a9d-9855-ea75170ff5c5">0001521951</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV80L2ZyYWc6NGE2Mjc1YTRhNzA2NDgzOWIyZjEwZDJiMTcwYjEzZTAvdGFibGU6MGQyZjlkOTRkMTlmNDg3NGFjYzA2NzA0YzU5YTFmOTUvdGFibGVyYW5nZTowZDJmOWQ5NGQxOWY0ODc0YWNjMDY3MDRjNTlhMWY5NV81LTEtMS0xLTE3NDIwMQ_159a0163-b3c8-45db-9033-6304022da9c1">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDgy_7593f143-e6b6-4943-bae4-bc55d1b3d16e">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8yMjU_545a82e3-11a7-4480-8313-8e85c34269c0">2023-04-28</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDgz_806fc6e8-a0b7-43e7-ba99-f9c592e6840e">First Business Financial Services, Inc.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6NmU2OGQzYTZlNDEyNGEzMGI0NGE3MzQzMWFlNjc0OGEvdGFibGVyYW5nZTo2ZTY4ZDNhNmU0MTI0YTMwYjQ0YTczNDMxYWU2NzQ4YV8xLTAtMS0xLTE3NDIwMQ_1854117a-7a74-495f-b5d3-662967814d48">WI</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6NmU2OGQzYTZlNDEyNGEzMGI0NGE3MzQzMWFlNjc0OGEvdGFibGVyYW5nZTo2ZTY4ZDNhNmU0MTI0YTMwYjQ0YTczNDMxYWU2NzQ4YV8xLTItMS0xLTE3NDIwMQ_b5542f26-4b5d-46f2-8994-639704971399">1-34095</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6NmU2OGQzYTZlNDEyNGEzMGI0NGE3MzQzMWFlNjc0OGEvdGFibGVyYW5nZTo2ZTY4ZDNhNmU0MTI0YTMwYjQ0YTczNDMxYWU2NzQ4YV8xLTQtMS0xLTE3NDIwMQ_3bf3c78e-9c77-44b9-8e36-d2fcfa1c566d">39-1576570</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDg0_ae5fc42f-cccb-4627-bdd9-dcddbe99d01c">401 Charmany Drive</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDc5_bd4035d7-1206-4e95-b2c1-b038ac43c9a1">Madison</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDg1_37f88271-cfe6-49dd-8fbc-f4e9ec35f1a3">WI</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDg2_6c053de8-9236-4366-9cd1-571b4be79d7b">53719</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDgw_12bd0677-d29b-40e7-bf7f-defb2c3fafba">608</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDg3_c4c9d490-32c2-493a-be27-876a8b818d57">238-8008</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6NmU3YjA2N2VmMjUxNGQxMGFmNTE3ZDFkZDA0Y2IzYWUvdGFibGVyYW5nZTo2ZTdiMDY3ZWYyNTE0ZDEwYWY1MTdkMWRkMDRjYjNhZV8wLTAtMS0xLTE3NDIwMQ_337587f1-bfea-48f5-a740-a76f7d9efb9e">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6NThjZjE4Y2NjMWFiNDMyNDgwNWQ4MDU2MTRmMmQ4ZjUvdGFibGVyYW5nZTo1OGNmMThjY2MxYWI0MzI0ODA1ZDgwNTYxNGYyZDhmNV8wLTAtMS0xLTE3NDIwMQ_ddeeb72e-e337-45b1-b52c-fdc94eb75b23">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6ZWEzM2Q1M2Y5YWVhNGE2YTg0MjY5OWQxYjY5OGY2YmEvdGFibGVyYW5nZTplYTMzZDUzZjlhZWE0YTZhODQyNjk5ZDFiNjk4ZjZiYV8wLTAtMS0xLTE3NDIwMQ_b4b92e8a-63eb-4eb4-81d8-bcd4e2149cdc">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6OThhMDY4NjdhMWE5NDAzNWI3ZTY3ODAzZDI2OWQ2ZDIvdGFibGVyYW5nZTo5OGEwNjg2N2ExYTk0MDM1YjdlNjc4MDNkMjY5ZDZkMl8wLTAtMS0xLTE3NDIwMQ_ee404ecd-5dfc-4431-92fe-bb49379aef62">false</dei:PreCommencementIssuerTenderOffer>
    <dei:EntityEmergingGrowthCompany
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGV4dHJlZ2lvbjowYzI0ODhlZmY3NWU0YmFmYTRjY2JlNTA4YjY2NjE2MV8zMDgx_3967fffa-edf7-4a18-9028-99a6002ba22b">false</dei:EntityEmergingGrowthCompany>
    <dei:Security12bTitle
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6MTVjMWNjYWM3ZmFiNGFkYmFlZDkwZjQzMWY4YWEzODUvdGFibGVyYW5nZToxNWMxY2NhYzdmYWI0YWRiYWVkOTBmNDMxZjhhYTM4NV8xLTAtMS0xLTE3NDIwMQ_1e7ec838-33a4-4739-a754-0b7c978fc71b">Common Stock, $0.01 par value</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6MTVjMWNjYWM3ZmFiNGFkYmFlZDkwZjQzMWY4YWEzODUvdGFibGVyYW5nZToxNWMxY2NhYzdmYWI0YWRiYWVkOTBmNDMxZjhhYTM4NV8xLTItMS0xLTE3NDIwMQ_c0f635d4-90d0-458e-b00d-e3f2ad090764">FBIZ</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="i0bf39d8c7f404500a4ff2a7407d0bf35_D20230428-20230428"
      id="id3VybDovL2RvY3MudjEvZG9jOmE5OThhMjZkNDFkMDQ4MTQ4MzZmOWNlYjA4NGM3N2Q5L3NlYzphOTk4YTI2ZDQxZDA0ODE0ODM2ZjljZWIwODRjNzdkOV8xL2ZyYWc6MGMyNDg4ZWZmNzVlNGJhZmE0Y2NiZTUwOGI2NjYxNjEvdGFibGU6MTVjMWNjYWM3ZmFiNGFkYmFlZDkwZjQzMWY4YWEzODUvdGFibGVyYW5nZToxNWMxY2NhYzdmYWI0YWRiYWVkOTBmNDMxZjhhYTM4NV8xLTQtMS0xLTE3NDIwMQ_a3c99134-5a3e-4526-a910-e9ad71ef68d2">NASDAQ</dei:SecurityExchangeName>
</xbrl>
