Fair Value, Assets, Level 1 to Level 2 Transfers, Amount1

No definition available.

Name:	fbiz_FairValueAssetsLevel1toLevel2TransfersAmount1
Namespace Prefix:	fbiz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Assets, Level 2 to Level 1 Transfers, Amount1

+ References

No definition available.

+ Details

Name:	fbiz_FairValueAssetsLevel2toLevel1TransfersAmount1
Namespace Prefix:	fbiz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount1

+ References

No definition available.

+ Details

Name:	fbiz_FairValueLiabilitiesLevel1toLevel2TransfersAmount1
Namespace Prefix:	fbiz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount1

+ References

No definition available.

+ Details

Name:	fbiz_FairValueLiabilitiesLevel2toLevel1TransfersAmount1
Namespace Prefix:	fbiz_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Quantification of unobservable inputs for Level 3 values for impaired loans

+ References

No definition available.

+ Details

Name:	fbiz_QuantificationOfUnobservableInputsForLevel3ValuesForImpairedLoans
Namespace Prefix:	fbiz_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_AssetsFairValueDisclosureNonrecurring
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=fbiz_ImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=fbiz_ForeclosedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Disclosures (Narrative Disclosures) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information
Fair value, assets, level 1 to level 2 transfers	$ 0	$ 0
Fair value, assets, level 2 to Level 1 transfers	0	0
Fair value, assets, transfers into level 3	0	0
Fair value, assets, transfers out of level 3	0	0
Fair value, liabilities, level 1 to level 2 transfers	0	0
Fair value, liabilities, level 2 to level 1 transfers	0	0
Fair value, liabilities, transfers into level 3	0	0
Fair value, liabilities, transfers out of level 3	$ 0	$ 0
Minimum
Fair Value Inputs, Assets, Quantitative Information
Quantification of unobservable inputs for level 3 values for impaired loans	13.00%
Maximum
Fair Value Inputs, Assets, Quantitative Information
Quantification of unobservable inputs for level 3 values for impaired loans	75.00%
Weighted Average
Fair Value Inputs, Assets, Quantitative Information
Quantification of unobservable inputs for level 3 values for impaired loans	16.00%
Impaired loans
Fair Value Inputs, Assets, Quantitative Information
Assets measured on a non-recurring basis, fair value	$ 10,747,000		$ 15,147,000
Fair Value Measurements - Level 3 Inputs \| Impaired loans
Fair Value Inputs, Assets, Quantitative Information
Assets measured on a non-recurring basis, fair value	6,414,000		5,084,000
Fair Value Measurements - Level 3 Inputs \| Foreclosed properties
Fair Value Inputs, Assets, Quantitative Information
Assets measured on a non-recurring basis, fair value	$ 0		$ 0