XML 28 R52.htm IDEA: XBRL DOCUMENT v2.4.1.9
Loans (Changes In The Allowance For Loan Losses) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance $ 27,637us-gaap_FinancingReceivableAllowanceForCreditLosses $ 26,736us-gaap_FinancingReceivableAllowanceForCreditLosses  
Charge-offs 4,570us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs 2,976us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs  
Recoveries 1,383us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery 1,286us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery  
Provision (credit) 2,741us-gaap_ProvisionForLoanLeaseAndOtherLosses 2,106us-gaap_ProvisionForLoanLeaseAndOtherLosses  
Ending balance 27,191us-gaap_FinancingReceivableAllowanceForCreditLosses 27,152us-gaap_FinancingReceivableAllowanceForCreditLosses  
Allowance for loan losses, Individually Evaluated for impairment 1,937us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1 1,323us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1  
Allowance for loan losses, Collectively Evaluated for impairment 25,254us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment 25,829us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment  
Loans, Ending balance 1,892,390us-gaap_NotesReceivableGross 1,817,471us-gaap_NotesReceivableGross 1,881,071us-gaap_NotesReceivableGross
Loans, Individually Evaluated for impairment 7,998us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment 13,251us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment  
Loans, Collectively Evaluated for impairment 1,884,392us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment 1,804,220us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment  
Commercial Business [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 5,621us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,273us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Charge-offs 1,141us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
68us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Recoveries 48us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
29us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Provision (credit) 867us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
455us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Ending balance 5,395us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,689us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Allowance for loan losses, Individually Evaluated for impairment 1,120us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
397us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Allowance for loan losses, Collectively Evaluated for impairment 4,275us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
4,292us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Loans, Ending balance 277,427us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
268,308us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
267,377us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
Loans, Individually Evaluated for impairment 4,587us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
3,706us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Loans, Collectively Evaluated for impairment 272,840us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
264,602us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_CommercialAndIndustrialMember
 
Commercial Mortgage [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 8,122us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
7,743us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Charge-offs 609us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
   
Recoveries 89us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
7us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Provision (credit) 554us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
230us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Ending balance 8,156us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
7,980us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Allowance for loan losses, Individually Evaluated for impairment 817us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
926us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Allowance for loan losses, Collectively Evaluated for impairment 7,339us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
7,054us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Loans, Ending balance 480,479us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
469,725us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
476,407us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Loans, Individually Evaluated for impairment 3,411us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
9,545us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Loans, Collectively Evaluated for impairment 477,068us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
460,180us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
 
Residential Mortgage [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 570us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
676us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Charge-offs 55us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
78us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Recoveries 33us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
21us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Provision (credit) 10us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
53us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Ending balance 558us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
672us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Allowance for loan losses, Collectively Evaluated for impairment 558us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
672us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Loans, Ending balance 97,850us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
110,290us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
100,241us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
Loans, Collectively Evaluated for impairment 97,850us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
110,290us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialMortgageMember
 
Home Equity [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 1,485us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,367us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Charge-offs 84us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
106us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Recoveries 10us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
11us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Provision (credit) 19us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
99us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Ending balance 1,430us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,371us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Allowance for loan losses, Collectively Evaluated for impairment 1,430us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
1,371us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Loans, Ending balance 380,070us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
326,744us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
379,774us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
Loans, Collectively Evaluated for impairment 380,070us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
326,744us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_HomeEquityMember
 
Consumer Indirect [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 11,383us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
12,230us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Charge-offs 2,422us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
2,455us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Recoveries 1,105us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
1,105us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Provision (credit) 1,139us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
1,104us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Ending balance 11,205us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
11,984us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Allowance for loan losses, Collectively Evaluated for impairment 11,205us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
11,984us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Loans, Ending balance 637,380us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
620,916us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
636,357us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
Loans, Collectively Evaluated for impairment 637,380us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
620,916us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= fisi_ConsumerIndirectMember
 
Other Consumer [Member]      
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning balance 456us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
447us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Charge-offs 259us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
269us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Recoveries 98us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
113us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Provision (credit) 152us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
165us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Ending balance 447us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
456us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Allowance for loan losses, Collectively Evaluated for impairment 447us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
456us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
 
Loans, Ending balance 19,184us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
21,488us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
20,915us-gaap_NotesReceivableGross
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
Loans, Collectively Evaluated for impairment $ 19,184us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember
$ 21,488us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerOtherFinancingReceivableMember