XML 54 R45.htm IDEA: XBRL DOCUMENT
v3.23.1

Restructuring Charges (Narrative) (Details) $ in Thousands |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Jul. 17, 2020 Branch | Oct. 31, 2020 Branch | Mar. 31, 2023 USD ($) | Mar. 31, 2022 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2020 USD ($)
Restructuring Cost And Reserve [Line Items] |  |  |  |  |  |  |
Number of bank branch closure | Branch | 6 |  |  |  |  |  |
Percentage of branch network | 10.00% |  |  |  |  |  |
Percentage of branch network impact | 6.00% |  |  |  |  |  |
Number of additional branches planned to close | Branch |  | 1 |  |  |  |  |
Pre tax expense related branch closures |  |  |  |  |  |  | $ 1,700
Restructuring Charges |  |  |  | $ 1,600 | $ 111 |  |
Restructuring charges |  |  | $ 0 |  |  |  |
Long lived assets held for sale |  |  | $ 1,500 |  |  | $ 1,500 |
Employee Severance [Member] |  |  |  |  |  |  |
Restructuring Cost And Reserve [Line Items] |  |  |  |  |  |  |
Pre tax expense related branch closures |  |  |  |  |  |  | 200
Lease Termination Costs [Member] |  |  |  |  |  |  |
Restructuring Cost And Reserve [Line Items] |  |  |  |  |  |  |
Pre tax expense related branch closures |  |  |  |  |  |  | 500
Valuation Adjustments On Branch Facilities [Member] |  |  |  |  |  |  |
Restructuring Cost And Reserve [Line Items] |  |  |  |  |  |  |
Pre tax expense related branch closures |  |  |  |  |  |  | $ 1,000

X
- Definition Number of additional branches planned to close. + References No definition available. + Details
Name: | fisi_NumberOfAdditionalBranchesPlannedToClose
Namespace Prefix: | fisi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of bank branch closure. + References No definition available. + Details
Name: | fisi_NumberOfBankBranchClosure
Namespace Prefix: | fisi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of branch network. + References No definition available. + Details
Name: | fisi_PercentageOfBranchNetwork
Namespace Prefix: | fisi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of branch network impact. + References No definition available. + Details
Name: | fisi_PercentageOfBranchNetworkImpact
Namespace Prefix: | fisi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Pre tax expense related branch closures. + References No definition available. + Details
Name: | fisi_PreTaxExpenseRelatedBranchClosures
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI https://asc.fasb.org/extlink&oid=126905981&loc=d3e2420-110228 + Details
Name: | us-gaap_ImpairmentOfLongLivedAssetsHeldForUse
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 45 -Paragraph 3 -URI https://asc.fasb.org/extlink&oid=109237686&loc=d3e17752-110868 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.P.3) -URI https://asc.fasb.org/extlink&oid=115931487&loc=d3e140864-122747 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)(1)) -URI https://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747 + Details
Name: | us-gaap_RestructuringCharges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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_RestructuringCostAndReserveLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
Name: | us-gaap_RestructuringCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=us-gaap_EmployeeSeveranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=fisi_LeaseTerminationCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringCostAndReserveAxis=fisi_ValuationAdjustmentsOnBranchFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |