XML 90 R80.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Loans (Retail Loan Portfolio Categorized by Performance Status) (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Residential Real Estate Loans [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | $ 112,704 | $ 79,882
Prior Fiscal Year 1 | 80,501 | 86,126
Prior Fiscal Year 2 | 81,513 | 119,329
Prior Fiscal Year 3 | 110,955 | 77,232
Prior Fiscal Year 4 | 71,462 | 56,197
Prior | 192,687 | 171,194
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 649,822 | 589,960
Residential Real Estate Loans [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 112,704 | 79,882
Prior Fiscal Year 1 | 80,117 | 85,821
Prior Fiscal Year 2 | 80,323 | 118,819
Prior Fiscal Year 3 | 109,601 | 76,437
Prior Fiscal Year 4 | 70,325 | 55,520
Prior | 190,388 | 169,410
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 643,458 | 585,889
Residential Real Estate Loans [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 | 0
Prior Fiscal Year 1 | 384 | 305
Prior Fiscal Year 2 | 1,190 | 510
Prior Fiscal Year 3 | 1,354 | 795
Prior Fiscal Year 4 | 1,137 | 677
Prior | 2,299 | 1,784
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 6,364 | 4,071
Residential Real Estate Loans [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 |
Prior Fiscal Year 1 | 0 |
Prior Fiscal Year 2 | 0 |
Prior Fiscal Year 3 | 0 |
Prior Fiscal Year 4 | 32 |
Prior | 95 |
Revolving Loans Amortized Cost Basis | 0 |
Revolving Loans Converted to Term | 0 |
Total | 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 | 72,183 | 70,976
Revolving Loans Converted to Term | 5,184 | 6,694
Total | 77,367 | 77,670
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 | 72,128 | 70,942
Revolving Loans Converted to Term | 5,018 | 6,586
Total | 77,146 | 77,528
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 | 55 | 34
Revolving Loans Converted to Term | 166 | 108
Total | 221 | 142
Residential Real Estate Lines [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 0 |
Prior Fiscal Year 1 | 0 |
Prior Fiscal Year 2 | 0 |
Prior Fiscal Year 3 | 0 |
Prior Fiscal Year 4 | 0 |
Prior | 0 |
Revolving Loans Amortized Cost Basis | 28 |
Revolving Loans Converted to Term | 13 |
Total | 41 |
Consumer Indirect [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 247,918 | 441,080
Prior Fiscal Year 1 | 337,452 | 333,111
Prior Fiscal Year 2 | 234,164 | 127,096
Prior Fiscal Year 3 | 79,032 | 60,362
Prior Fiscal Year 4 | 31,315 | 39,557
Prior | 18,950 | 22,414
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 948,831 | 1,023,620
Consumer Indirect [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 247,194 | 440,332
Prior Fiscal Year 1 | 336,369 | 331,902
Prior Fiscal Year 2 | 232,891 | 126,664
Prior Fiscal Year 3 | 78,652 | 59,981
Prior Fiscal Year 4 | 31,091 | 39,352
Prior | 18,820 | 22,310
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 945,017 | 1,020,541
Consumer Indirect [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 724 | 748
Prior Fiscal Year 1 | 1,083 | 1,209
Prior Fiscal Year 2 | 1,273 | 432
Prior Fiscal Year 3 | 380 | 381
Prior Fiscal Year 4 | 224 | 205
Prior | 130 | 104
Revolving Loans Amortized Cost Basis | 0 | 0
Revolving Loans Converted to Term | 0 | 0
Total | 3,814 | 3,079
Consumer Indirect [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 1,371 |
Prior Fiscal Year 1 | 6,279 |
Prior Fiscal Year 2 | 5,845 |
Prior Fiscal Year 3 | 1,787 |
Prior Fiscal Year 4 | 1,282 |
Prior | 1,459 |
Revolving Loans Amortized Cost Basis | 0 |
Revolving Loans Converted to Term | 0 |
Total | 18,023 |
Other Consumer [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 35,496 | 6,463
Prior Fiscal Year 1 | 3,990 | 2,664
Prior Fiscal Year 2 | 1,424 | 2,043
Prior Fiscal Year 3 | 949 | 761
Prior Fiscal Year 4 | 217 | 213
Prior | 256 | 308
Revolving Loans Amortized Cost Basis | 2,768 | 2,658
Revolving Loans Converted to Term | 0 | 0
Total | 45,100 | 15,110
Other Consumer [Member] | Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 35,483 | 6,463
Prior Fiscal Year 1 | 3,990 | 2,664
Prior Fiscal Year 2 | 1,424 | 2,043
Prior Fiscal Year 3 | 949 | 761
Prior Fiscal Year 4 | 217 | 213
Prior | 256 | 308
Revolving Loans Amortized Cost Basis | 2,747 | 2,656
Revolving Loans Converted to Term | 0 | 0
Total | 45,066 | 15,108
Other Consumer [Member] | Non-Performing [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 13 | 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 | 21 | 2
Revolving Loans Converted to Term | 0 | 0
Total | 34 | $ 2
Other Consumer [Member] | Current Period Gross Write-offs [Member] |  |
Financing Receivable Recorded Investment [Line Items] |  |
Current Fiscal Year | 902 |
Prior Fiscal Year 1 | 127 |
Prior Fiscal Year 2 | 105 |
Prior Fiscal Year 3 | 52 |
Prior Fiscal Year 4 | 31 |
Prior | 20 |
Revolving Loans Amortized Cost Basis | 47 |
Revolving Loans Converted to Term | 0 |
Total | $ 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 Financing receivable (payable) originated five or more years before latest fiscal year. + References No definition available. + Details
Name: | fisi_FinancingReceivablePayableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear
Namespace Prefix: | fisi_
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://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 2: 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: |