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v3.19.3.a.u2

Nature of Operations and Summary of Significant Accounting Policies Direct Financing Leases (Details) | 12 Months Ended
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Dec. 31, 2019
Minimum |
Unguaranteed Residual Percentage Of Cost [Line Items] |
Unguaranteed residual percent of cost | 3.00%
Maximum |
Unguaranteed Residual Percentage Of Cost [Line Items] |
Unguaranteed residual percent of cost | 20.00%

X
- Definition Unguaranteed Residual Percent Of Cost + References No definition available. + Details
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Namespace Prefix: | fbiz_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition [Line Items] for Unguaranteed Residual Percentage Of Cost [Table] + References No definition available. + Details
Name: | fbiz_UnguaranteedResidualPercentageOfCostLineItems
Namespace Prefix: | fbiz_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |