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Loan and Lease Receivables, Impaired Loans and Leases and Allowance for Loan and Lease Losses (Impaired Loans and Leases) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Recorded investment
With no impairment reserve recorded	$ 10,475us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment		$ 11,270us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
With impairment reserve recorded	849us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment		525us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Total	11,324us-gaap_ImpairedFinancingReceivableRecordedInvestment		11,795us-gaap_ImpairedFinancingReceivableRecordedInvestment
Unpaid principal balance
With no impairment reserve recorded	15,112us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance		15,623us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
With impairment reserve recorded	889us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance		565us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Total	16,001us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance		16,188us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Impairment reserve
Impairment reserve	391us-gaap_ImpairedFinancingReceivableRelatedAllowance		290us-gaap_ImpairedFinancingReceivableRelatedAllowance
Average recorded investment(1)
With no impairment reserve recorded	11,442us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment	[1]	13,926us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment	[1]
With impairment reserve recorded	519us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment	[1]	548us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment	[1]
Total	11,961us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment	[1]	14,474us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment	[1]
Foregone interest income
With no impairment reserve recorded	167fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome		843fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome
With impairment reserve recorded	12fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome		27fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome
Foregone interest income	179fbiz_ImpairedFinancingReceivableForegoneInterestIncome		870fbiz_ImpairedFinancingReceivableForegoneInterestIncome
Interest income recognized
With no impairment reserve recorded	1us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod		740us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
Total	1us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod		740us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Net foregone interest income
With no impairment reserve recorded	166fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome		103fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome
With impairment reserve recorded	12fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome		27fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome
Total	178fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome		130fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome
Commercial real estate — owner occupied
Recorded investment
With no impairment reserve recorded	568us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		577us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Total	568us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		577us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Unpaid principal balance
With no impairment reserve recorded	568us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		577us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Total	568us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		577us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Impairment reserve
Impairment reserve	0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Average recorded investment(1)
With no impairment reserve recorded	573us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]	484us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]
Total	573us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]	484us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember	[1]
Foregone interest income
With no impairment reserve recorded	6fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		30fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Foregone interest income	6fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		30fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		79us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		79us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Net foregone interest income
With no impairment reserve recorded	6fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		(49)fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Total	6fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember		(49)fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableOwnerOccupiedMember
Commercial real estate — non-owner occupied
Recorded investment
With no impairment reserve recorded	919us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		921us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
With impairment reserve recorded	48us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		49us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Total	967us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		970us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Unpaid principal balance
With no impairment reserve recorded	919us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		921us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
With impairment reserve recorded	88us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		89us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Total	1,007us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		1,010us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Impairment reserve
Impairment reserve	48us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		49us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Average recorded investment(1)
With no impairment reserve recorded	921us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]	349us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]
With impairment reserve recorded	48us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]	52us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]
Total	969us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]	401us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember	[1]
Foregone interest income
With no impairment reserve recorded	3fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		22fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
With impairment reserve recorded	1fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		4fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Foregone interest income	4fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		26fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Net foregone interest income
With no impairment reserve recorded	3fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		22fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
With impairment reserve recorded	1fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		4fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Total	4fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember		26fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableNonOwnerOccupiedMember
Construction and land development
Recorded investment
With no impairment reserve recorded	5,068us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		5,157us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Total	5,068us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		5,157us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Unpaid principal balance
With no impairment reserve recorded	7,738us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		7,828us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Total	7,738us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		7,828us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Impairment reserve
Impairment reserve	0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Average recorded investment(1)
With no impairment reserve recorded	5,135us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]	5,285us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]
Total	5,135us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]	5,285us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember	[1]
Foregone interest income
With no impairment reserve recorded	37fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		155fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Foregone interest income	37fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		155fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Net foregone interest income
With no impairment reserve recorded	37fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		155fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Total	37fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember		155fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableConstructionAndLandDevelopmentMember
Multi-family
Recorded investment
With no impairment reserve recorded	14us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		17us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Total	14us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		17us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Unpaid principal balance
With no impairment reserve recorded	380us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		384us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Total	380us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		384us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Impairment reserve
Impairment reserve	0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Average recorded investment(1)
With no impairment reserve recorded	15us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]	24us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]
Total	15us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]	24us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember	[1]
Foregone interest income
With no impairment reserve recorded	13fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		53fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Foregone interest income	13fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		53fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Net foregone interest income
With no impairment reserve recorded	13fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		53fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
Total	13fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember		53fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivableMultiFamilyMember
1-4 family
Recorded investment
With no impairment reserve recorded	1,351us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		1,181us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
With impairment reserve recorded	427us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		390us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Total	1,778us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		1,571us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Unpaid principal balance
With no impairment reserve recorded	1,361us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		1,218us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
With impairment reserve recorded	427us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		390us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Total	1,788us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		1,608us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Impairment reserve
Impairment reserve	159us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		155us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Average recorded investment(1)
With no impairment reserve recorded	1,459us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]	380us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]
With impairment reserve recorded	386us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]	405us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]
Total	1,845us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]	785us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember	[1]
Foregone interest income
With no impairment reserve recorded	10fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		15fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
With impairment reserve recorded	5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		18fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Foregone interest income	15fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		33fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		12us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		12us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Net foregone interest income
With no impairment reserve recorded	10fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		3fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
With impairment reserve recorded	5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		18fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Total	15fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember		21fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialRealEstateLoansReceivable14FamilyMember
Commercial and industrial
Recorded investment
With no impairment reserve recorded	1,482us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		2,316us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
With impairment reserve recorded	322us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		33us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Total	1,804us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		2,349us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Unpaid principal balance
With no impairment reserve recorded	2,406us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		2,926us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
With impairment reserve recorded	322us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		33us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Total	2,728us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		2,959us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Impairment reserve
Impairment reserve	132us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		33us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Average recorded investment(1)
With no impairment reserve recorded	2,252us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]	6,141us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]
With impairment reserve recorded	33us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]	34us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]
Total	2,285us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]	6,175us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember	[1]
Foregone interest income
With no impairment reserve recorded	74fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		463fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
With impairment reserve recorded	5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Foregone interest income	79fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		463fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Interest income recognized
With no impairment reserve recorded	1us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		649us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Total	1us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		649us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Net foregone interest income
With no impairment reserve recorded	73fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		(186)fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
With impairment reserve recorded	5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Total	78fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember		(186)fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_CommercialAndIndustrialLoansReceivableMember
Direct financing leases, net
Recorded investment
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Total	0us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Unpaid principal balance
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Total	0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Impairment reserve
Impairment reserve	0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Average recorded investment(1)
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]
Total	0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]	0us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember	[1]
Foregone interest income
With no impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Foregone interest income	0fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Net foregone interest income
With no impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Total	0fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember		0fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_FinanceLeasesFinancingReceivableMember
Home equity and second mortgages
Recorded investment
With no impairment reserve recorded	371us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		380us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
With impairment reserve recorded	52us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		53us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Total	423us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		433us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Unpaid principal balance
With no impairment reserve recorded	371us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		380us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
With impairment reserve recorded	52us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		53us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Total	423us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		433us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Impairment reserve
Impairment reserve	52us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		53us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Average recorded investment(1)
With no impairment reserve recorded	375us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]	495us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]
With impairment reserve recorded	52us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]	57us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]
Total	427us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]	552us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember	[1]
Foregone interest income
With no impairment reserve recorded	4fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		18fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
With impairment reserve recorded	1fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Foregone interest income	5fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		23fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Net foregone interest income
With no impairment reserve recorded	4fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		18fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
With impairment reserve recorded	1fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		5fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Total	5fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember		23fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_HomeEquityLoansAndSecondMortageLoansReceivableMember
Other
Recorded investment
With no impairment reserve recorded	702us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		721us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Total	702us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		721us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Unpaid principal balance
With no impairment reserve recorded	1,369us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		1,389us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Total	1,369us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		1,389us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Impairment reserve
Impairment reserve	0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Average recorded investment(1)
With no impairment reserve recorded	712us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]	768us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]
Total	712us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]	768us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember	[1]
Foregone interest income
With no impairment reserve recorded	20fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		87fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Foregone interest income	20fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		87fbiz_ImpairedFinancingReceivableForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Interest income recognized
With no impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
With impairment reserve recorded	0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Total	0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Net foregone interest income
With no impairment reserve recorded	20fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		87fbiz_ImpairedFinancingReceivableWithNoRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
With impairment reserve recorded	0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		0fbiz_ImpairedFinancingReceivableWithRelatedAllowanceNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
Total	$ 20fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember		$ 87fbiz_ImpairedFinancingReceivableNetForegoneInterestIncome / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = fbiz_OtherLoansReceivableMember
[1] (1)Average recorded investment is calculated primarily using daily average balances.

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