XML 148 R131.htm IDEA: XBRL DOCUMENT
v3.22.4

Fair Value Measurements (Additional Quantitative Information about Assets Measured at Fair Value on Recurring and Non-Recurring Basis) (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 USD ($)
Collateral Dependent Loans [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets at fair value | $ 21,454 |
Collateral Dependent Loans [Member] | Weighted Average [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 12.30% | [1],[2],[3]
Collateral Dependent Loans [Member] | Minimum [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 0.00% |
Collateral Dependent Loans [Member] | Maximum [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 20.00% |
Loan Servicing Rights [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets at fair value | $ 1,470 |
Loan Servicing Rights [Member] | Weighted Average [Member] | Discounted Cash Flow [Member] | Discount Rate [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 10.40% | [3]
Loan Servicing Rights [Member] | Weighted Average [Member] | Discounted Cash Flow [Member] | Constant Prepayment Rate [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 11.60% | [3]
Long-lived Assets Held for Sale [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets at fair value | $ 1,509 |
Long-lived Assets Held for Sale [Member] | Minimum [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 11.00% | [1],[2]
Long-lived Assets Held for Sale [Member] | Maximum [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 108.00% | [1],[2]
Other Real Estate Owned [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets at fair value | $ 19 |
Other Real Estate Owned [Member] | Appraisal of Collateral [Member] | Appraisal Adjustments [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Unobservable Input Value or Range | 10.00% | [1],[2]
[1] | Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated liquidation expenses.
[2] | Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable.
[3] | Weighted averages.

X
- Definition Fair value measurement with unobservable input value percentage. + References No definition available. + Details
Name: | fisi_FairValueMeasurementWithUnobservableInputValuePercentage
Namespace Prefix: | fisi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
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 No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=fisi_CollateralDependentFinancingReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=fisi_ValuationTechniqueAppraisalOfCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputComparabilityAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=fisi_LoanServicingRightsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=us-gaap_ValuationTechniqueDiscountedCashFlowMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputConstantPrepaymentRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=fisi_LongLivedAssetsHeldForSaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=fisi_OtherRealEstateOwnedOtherReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |