Accrued Interest Receivable on AFS Debt Securities

No definition available.

Name:	fbiz_AccruedInterestReceivableOnAFSDebtSecurities
Namespace Prefix:	fbiz_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before allowance for credit loss, of accrued interest on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

+ Details

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

- Definition

Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319

+ Details

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

- Definition

Amount, before allowance for credit loss, of accrued interest on financing receivable.

+ References

+ Details

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before allowance and fees, of loans and leases receivable. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

+ Details

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

- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82919202-210446

+ Details

Name:	us-gaap_OffBalanceSheetCreditLossLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 4.E)
-URI https://asc.fasb.org/extlink&oid=122038336&loc=d3e74512-122707

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(31))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_StockholdersEquity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialRealEstateLoansReceivableConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_CommercialandIndustrialLoansandLeasesReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fbiz_OtherLoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Nature of Operations and Summary of Significant Accounting Policies (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	$ 2,539,276,000	$ 2,443,215,000
Financing Receivable, Allowance for Credit Loss	26,140,000	24,230,000	$ 23,669,000	$ 24,336,000
Net deferred tax asset	11,458,000	11,711,000
Off-Balance-Sheet, Credit Loss, Liability	1,410,000	0
Stockholders' Equity Attributable to Parent	(266,581,000)	(260,640,000)	(245,051,000)	(232,422,000)
Debt Securities, Held-to-Maturity, Accrued Interest, before Allowance for Credit Loss	74,000,000
Financing Receivable, Accrued Interest, before Allowance for Credit Loss	8,900,000
Accrued Interest Receivable on AFS Debt Securities	1,000,000
Commercial real estate — owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	233,725,000	268,354,000
Financing Receivable, Allowance for Credit Loss	1,636,000	1,766,000
Off-Balance-Sheet, Credit Loss, Liability	20,000
Commercial real estate — non-owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	675,087,000	687,091,000
Financing Receivable, Allowance for Credit Loss	4,915,000	5,108,000
Off-Balance-Sheet, Credit Loss, Liability	51,000
Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	212,916,000	218,751,000
Financing Receivable, Allowance for Credit Loss	1,586,000	1,646,000
Off-Balance-Sheet, Credit Loss, Liability	701,000
Multi-family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	384,043,000	350,026,000
Financing Receivable, Allowance for Credit Loss	2,892,000	2,634,000
Off-Balance-Sheet, Credit Loss, Liability	9,000
1-4 family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	23,404,000	17,728,000
Financing Receivable, Allowance for Credit Loss	201,000	207,000
Off-Balance-Sheet, Credit Loss, Liability	20,000
Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	963,328,000	853,327,000
Financing Receivable, Allowance for Credit Loss	14,348,000	12,403,000	$ 8,912,000	$ 8,413,000
Off-Balance-Sheet, Credit Loss, Liability	557,000
Consumer and other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross	46,773,000	47,938,000
Financing Receivable, Allowance for Credit Loss	562,000	466,000
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross		0
Financing Receivable, Allowance for Credit Loss	1,818,000	484,000
Net deferred tax asset		465,000
Off-Balance-Sheet, Credit Loss, Liability		1,334,000
Stockholders' Equity Attributable to Parent		(1,353,000)
Cumulative Effect, Period of Adoption, Adjustment \| Commercial real estate — owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	(204,000)	(218,000)
Cumulative Effect, Period of Adoption, Adjustment \| Commercial real estate — non-owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	(242,000)	(297,000)
Cumulative Effect, Period of Adoption, Adjustment \| Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	796,000	109,000
Cumulative Effect, Period of Adoption, Adjustment \| Multi-family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	(386,000)	(391,000)
Cumulative Effect, Period of Adoption, Adjustment \| 1-4 family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	(45,000)	(60,000)
Cumulative Effect, Period of Adoption, Adjustment \| Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 1,873,000	1,359,000
Cumulative Effect, Period of Adoption, Adjustment \| Consumer and other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		(18,000)
Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans and Leases Receivable, before Fees, Gross		2,443,215,000
Financing Receivable, Allowance for Credit Loss		24,714,000
Net deferred tax asset		12,176,000
Off-Balance-Sheet, Credit Loss, Liability		1,334,000
Stockholders' Equity Attributable to Parent		(259,287,000)
Cumulative Effect, Period of Adoption, Adjusted Balance \| Commercial real estate — owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		1,548,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| Commercial real estate — non-owner occupied
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		4,811,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| Construction
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		1,755,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| Multi-family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		2,243,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| 1-4 family
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		147,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| Commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		13,762,000
Cumulative Effect, Period of Adoption, Adjusted Balance \| Consumer and other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		$ 448,000