XML 130 R69.htm IDEA: XBRL DOCUMENT v2.4.1.9
Loans (Changes In The Allowance For Loan Losses) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance $ 26,736us-gaap_FinancingReceivableAllowanceForCreditLosses $ 24,714us-gaap_FinancingReceivableAllowanceForCreditLosses $ 23,260us-gaap_FinancingReceivableAllowanceForCreditLosses
Charge-offs (12,014)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs (11,478)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs (9,568)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Recoveries 5,126us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery 4,421us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery 3,894us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
Provision (credit) 7,789us-gaap_ProvisionForLoanLeaseAndOtherLosses 9,079us-gaap_ProvisionForLoanLeaseAndOtherLosses 7,128us-gaap_ProvisionForLoanLeaseAndOtherLosses
Loans, Ending balance 1,881,071us-gaap_NotesReceivableGross 1,802,105us-gaap_NotesReceivableGross 1,675,453us-gaap_NotesReceivableGross
Loans, Individually Evaluated for impairment 7,308us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment 13,137us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment 5,212us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Loans, Collectively Evaluated for impairment 1,873,763us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment 1,788,968us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment 1,670,241us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Ending balance 27,637us-gaap_FinancingReceivableAllowanceForCreditLosses 26,736us-gaap_FinancingReceivableAllowanceForCreditLosses 24,714us-gaap_FinancingReceivableAllowanceForCreditLosses
Allowance for loan losses, Individually Evaluated for impairment 2,467us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 1,258us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 974us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Allowance for loan losses, Collectively Evaluated for impairment 25,170us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment 25,478us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment 23,740us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Commercial Business [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 4,273us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,884us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,036us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Charge-offs (204)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
(1,070)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
(729)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Recoveries 201us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
349us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
336us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Provision (credit) 1,351us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
110us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
1,241us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Loans, Ending balance 267,377us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
265,751us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
258,706us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Loans, Individually Evaluated for impairment 4,288us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
3,474us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
3,413us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Loans, Collectively Evaluated for impairment 263,089us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
262,277us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
255,293us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Ending balance 5,621us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,273us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,884us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Allowance for loan losses, Individually Evaluated for impairment 1,556us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
201us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
664us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Allowance for loan losses, Collectively Evaluated for impairment 4,065us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,072us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,220us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Commercial Mortgage [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 7,743us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
6,581us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
6,418us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Charge-offs (304)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
(553)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
(745)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Recoveries 143us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
319us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
261us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Provision (credit) 540us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
1,396us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
647us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Loans, Ending balance 476,407us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
470,312us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
414,282us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Loans, Individually Evaluated for impairment 3,020us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
9,663us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
1,799us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Loans, Collectively Evaluated for impairment 473,387us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
460,649us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
412,483us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Ending balance 8,122us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
7,743us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
6,581us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Allowance for loan losses, Individually Evaluated for impairment 911us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
1,057us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
310us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Allowance for loan losses, Collectively Evaluated for impairment 7,211us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
6,686us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
6,271us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Residential Mortgage [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 676us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
740us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
858us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Charge-offs (190)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
(411)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
(326)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Recoveries 39us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
54us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
130us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Provision (credit) 45us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
293us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
78us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Loans, Ending balance 100,241us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
113,101us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
133,341us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Loans, Collectively Evaluated for impairment 100,241us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
113,101us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
133,341us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Ending balance 570us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
676us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
740us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Allowance for loan losses, Collectively Evaluated for impairment 570us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
676us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
740us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Home Equity [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 1,367us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,282us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,242us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Charge-offs (340)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
(391)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
(305)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Recoveries 56us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
157us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
44us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Provision (credit) 402us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
319us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
301us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Loans, Ending balance 379,774us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
320,658us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
282,503us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Loans, Collectively Evaluated for impairment 379,774us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
320,658us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
282,503us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Ending balance 1,485us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,367us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,282us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Allowance for loan losses, Collectively Evaluated for impairment 1,485us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,367us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,282us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Consumer Indirect [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 12,230us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
10,715us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
10,189us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Charge-offs (10,004)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
(8,125)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
(6,589)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Recoveries 4,321us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
3,161us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
2,769us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Provision (credit) 4,836us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
6,479us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
4,346us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Loans, Ending balance 636,357us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
609,390us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
559,964us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Loans, Collectively Evaluated for impairment 636,357us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
609,390us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
559,964us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Ending balance 11,383us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
12,230us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
10,715us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Allowance for loan losses, Collectively Evaluated for impairment 11,383us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
12,230us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
10,715us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Other Consumer [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 447us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
512us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
517us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Charge-offs (972)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
(928)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
(874)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Recoveries 366us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
381us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
354us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Provision (credit) 615us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
482us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
515us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Loans, Ending balance 20,915us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
22,893us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
26,657us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Loans, Collectively Evaluated for impairment 20,915us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
22,893us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
26,657us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Ending balance 456us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
447us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
512us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Allowance for loan losses, Collectively Evaluated for impairment $ 456us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
$ 447us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
$ 512us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember