XML 65 R58.htm IDEA: XBRL DOCUMENT
v3.24.3

Loans (Retail Loan Portfolio Categorized by Performance Status) (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Residential Real Estate Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | $ 36,246 | $ 112,704
Prior Fiscal Year 1 | 113,485 | 80,501
Prior Fiscal Year 2 | 76,941 | 81,513
Prior Fiscal Year 3 | 77,209 | 110,955
Prior Fiscal Year 4 | 103,780 | 71,462
Prior | 240,580 | 192,687
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 648,241 | 649,822
Residential Real Estate Loans [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 36,246 | 112,704
Prior Fiscal Year 1 | 113,089 | 80,117
Prior Fiscal Year 2 | 76,412 | 80,323
Prior Fiscal Year 3 | 76,403 | 109,601
Prior Fiscal Year 4 | 102,516 | 70,325
Prior | 237,785 | 190,388
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 642,451 | 643,458
Residential Real Estate Loans [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 396 | 384
Prior Fiscal Year 2 | 529 | 1,190
Prior Fiscal Year 3 | 806 | 1,354
Prior Fiscal Year 4 | 1,264 | 1,137
Prior | 2,795 | 2,299
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 5,790 | 6,364
Residential Real Estate Loans [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 0 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 32
Prior | 109 | 95
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 109 | 127
Residential Real Estate Lines [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 0 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 0
Prior | 0 | 0
Revolving Loans Amortized Cost Basis | 71,681 | 72,183
Revolving Loans Converted to Term | 4,522 | 5,184
Total | 76,203 | 77,367
Residential Real Estate Lines [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 0 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 0
Prior | 0 | 0
Revolving Loans Amortized Cost Basis | 71,630 | 72,128
Revolving Loans Converted to Term | 4,341 | 5,018
Total | 75,971 | 77,146
Residential Real Estate Lines [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 0 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 0
Prior | 0 | 0
Revolving Loans Amortized Cost Basis | 51 | 55
Revolving Loans Converted to Term | 181 | 166
Total | 232 | 221
Residential Real Estate Lines [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 0 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 0
Prior | 0 | 0
Revolving Loans Amortized Cost Basis | 0 | 28
Revolving Loans Converted to Term | 0 | 13
Total | 0 | 41
Consumer Indirect [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 170,602 | 247,918
Prior Fiscal Year 1 | 200,904 | 337,452
Prior Fiscal Year 2 | 261,262 | 234,164
Prior Fiscal Year 3 | 169,325 | 79,032
Prior Fiscal Year 4 | 50,464 | 31,315
Prior | 22,094 | 18,950
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 874,651 | 948,831
Consumer Indirect [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 170,455 | 247,194
Prior Fiscal Year 1 | 200,312 | 336,369
Prior Fiscal Year 2 | 260,279 | 232,891
Prior Fiscal Year 3 | 168,344 | 78,652
Prior Fiscal Year 4 | 50,062 | 31,091
Prior | 21,908 | 18,820
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 871,360 | 945,017
Consumer Indirect [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 147 | 724
Prior Fiscal Year 1 | 592 | 1,083
Prior Fiscal Year 2 | 983 | 1,273
Prior Fiscal Year 3 | 981 | 380
Prior Fiscal Year 4 | 402 | 224
Prior | 186 | 130
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 3,291 | 3,814
Consumer Indirect [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 100 | 1,371
Prior Fiscal Year 1 | 3,585 | 6,279
Prior Fiscal Year 2 | 4,553 | 5,845
Prior Fiscal Year 3 | 3,475 | 1,787
Prior Fiscal Year 4 | 1,352 | 1,282
Prior | 1,308 | 1,459
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 14,373 | 18,023
Other Consumer [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 6,493 | 35,496
Prior Fiscal Year 1 | 30,580 | 3,990
Prior Fiscal Year 2 | 2,641 | 1,424
Prior Fiscal Year 3 | 872 | 949
Prior Fiscal Year 4 | 413 | 217
Prior | 266 | 256
Revolving Loans Amortized Cost Basis | 2,469 | 2,768
Revolving Loans Converted to Term | 0 | 0
Total | 43,734 | 45,100
Other Consumer [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 6,489 | 35,483
Prior Fiscal Year 1 | 30,578 | 3,990
Prior Fiscal Year 2 | 2,641 | 1,424
Prior Fiscal Year 3 | 872 | 949
Prior Fiscal Year 4 | 413 | 217
Prior | 259 | 256
Revolving Loans Amortized Cost Basis | 2,433 | 2,747
Revolving Loans Converted to Term | 0 | 0
Total | 43,685 | 45,066
Other Consumer [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 4 | 13
Prior Fiscal Year 1 | 2 | 0
Prior Fiscal Year 2 | 0 | 0
Prior Fiscal Year 3 | 0 | 0
Prior Fiscal Year 4 | 0 | 0
Prior | 7 | 0
Revolving Loans Amortized Cost Basis | 36 | 21
Revolving Loans Converted to Term | 0 | 0
Total | 49 | 34
Other Consumer [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 428 | 902
Prior Fiscal Year 1 | 79 | 127
Prior Fiscal Year 2 | 118 | 105
Prior Fiscal Year 3 | 25 | 52
Prior Fiscal Year 4 | 25 | 31
Prior | 4 | 20
Revolving Loans Amortized Cost Basis | 88 | 47
Revolving Loans Converted to Term | 0 | 0
Total | $ 767 | $ 1,284

X
- Definition Financing receivable after deferred income offset amount. + References No definition available. + Details
Name: | fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated more than five years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated four years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated in current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated in fiscal year prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated three years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of financing receivable originated two years prior to current fiscal year. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 29 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481962/310-10-50-29 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-5 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 + Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amortized cost of financing receivable that can be withdrawn, repaid, and redrawn. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6 + Details
Name: | us-gaap_FinancingReceivableRevolving
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost of revolving financing receivable converted to term loan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 79 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479294/326-20-55-79 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-6A + Details
Name: | us-gaap_FinancingReceivableRevolvingConvertedToTermLoan
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=fisi_CurrentPeriodGrossWriteOffsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fisi_ConsumerIndirectMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |