Loan and Lease Receivables, Impaired Loans and Leases and Allowance for Loan and Lease Losses (Allowance for Loan and Lease Losses) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Allowance for credit losses:
Beginning balance	$ 14,329	$ 13,901
Charge-offs	(324)	0
Recoveries	5	20
Provision	684	180
Ending balance	14,694	14,101
Ending balance: individually evaluated for impairment	292	507
Ending balance: collectively evaluated for impairment	14,303	13,594
Ending balance: loans acquired with deteriorated credit quality	99	0
Loans and lease receivables:
Total gross loans and leases receivable	1,298,067	986,221	1,281,792
Ending balance: individually evaluated for impairment	7,297	13,292
Ending balance: collectively evaluated for impairment	1,286,743	971,525
Ending balance: loans acquired with deteriorated credit quality	4,027	1,404
Allowance as % of gross loans	1.13%	1.43%	1.12%
Commercial real estate
Allowance for credit losses:
Beginning balance	8,619	9,055
Charge-offs	(11)	0
Recoveries	2	15
Provision	99	(98)
Ending balance	8,709	8,972
Ending balance: individually evaluated for impairment	207	208
Ending balance: collectively evaluated for impairment	8,502	8,764
Ending balance: loans acquired with deteriorated credit quality	0	0
Loans and lease receivables:
Total gross loans and leases receivable	814,446	638,701
Ending balance: individually evaluated for impairment	5,253	5,291
Ending balance: collectively evaluated for impairment	806,051	632,006
Ending balance: loans acquired with deteriorated credit quality	3,142	1,404
Allowance as % of gross loans	1.07%	1.40%
Commercial and industrial
Allowance for credit losses:
Beginning balance	5,067	4,235
Charge-offs	(313)	0
Recoveries	0	0
Provision	548	284
Ending balance	5,302	4,519
Ending balance: individually evaluated for impairment	33	239
Ending balance: collectively evaluated for impairment	5,170	4,280
Ending balance: loans acquired with deteriorated credit quality	99	0
Loans and lease receivables:
Total gross loans and leases receivable	426,413	303,630	416,654
Ending balance: individually evaluated for impairment	1,154	6,657
Ending balance: collectively evaluated for impairment	424,608	296,973
Ending balance: loans acquired with deteriorated credit quality	651	0
Allowance as % of gross loans	1.24%	1.49%
Consumer and other
Allowance for credit losses:
Beginning balance	218	273
Charge-offs	0	0
Recoveries	3	5
Provision	67	(2)
Ending balance	288	276
Ending balance: individually evaluated for impairment	52	60
Ending balance: collectively evaluated for impairment	236	216
Ending balance: loans acquired with deteriorated credit quality	0	0
Loans and lease receivables:
Total gross loans and leases receivable	25,564	17,526
Ending balance: individually evaluated for impairment	890	1,344
Ending balance: collectively evaluated for impairment	24,440	16,182
Ending balance: loans acquired with deteriorated credit quality	234	0
Allowance as % of gross loans	1.13%	1.57%
Direct financing leases, net
Allowance for credit losses:
Beginning balance	425	338
Charge-offs	0	0
Recoveries	0	0
Provision	(30)	(4)
Ending balance	395	334
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	395	334
Ending balance: loans acquired with deteriorated credit quality	0	0
Loans and lease receivables:
Total gross loans and leases receivable	31,644	26,364	34,165
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	31,644	26,364
Ending balance: loans acquired with deteriorated credit quality	$ 0	$ 0
Allowance as % of gross loans	1.25%	1.27%

Ratio of Allowance for Loan and Lease Losses to Total Gross Loans and Leases

No definition available.

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

- Definition

The balance of financing receivables that were acquired with deteriorated credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

The valuation allowance for financing receivables acquired with deteriorated credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(4)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Details

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

- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

- Details

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

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.11)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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