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Commitments and Contingencies Commitments and Contingencies (SBA Recourse Reserve) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract] |  |  |
Beginning Balance | $ 2,849 | $ 1,750 |
SBA recourse provision | 1,913 | 2,240 | $ 2,068
SBA Loan Charge Offs, Net | (1,806) | (1,141) |
Ending Balance | $ 2,956 | $ 2,849 | $ 1,750

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- Definition SBA Loan Charge Offs, Net + References No definition available. + Details
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- Definition SBA Recourse (Benefit) Provision + References No definition available. + Details
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Namespace Prefix: | fbiz_
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- Definition SBA Recourse Reserve + References No definition available. + Details
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Namespace Prefix: | fbiz_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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