XML 38 R31.htm IDEA: XBRL DOCUMENT
v3.25.3

Leases (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2025
Leases [Abstract] |
Summary of Classification of Right of Use Assets and Lease Liabilities | The following table represents the consolidated statements of financial condition classification of the Company’s right of use assets and lease liabilities (in thousands):
|  |  |  | September 30, |  |  | December 31, |
|  | Balance Sheet Location |  | 2025 |  |  | 2024 |
Operating Lease Right of Use Assets: |  |  |  |  |  |  |  |
Gross carrying amount |  | Other assets |  | $ | 40,002 |  |  | $ | 39,343 |
Accumulated amortization |  | Other assets |  |  | (10,342 | ) |  |  | (8,974 | )
Net book value |  |  |  | $ | 29,660 |  |  | $ | 30,369 |
Operating Lease Liabilities: |  |  |  |  |  |  |  |
Right of use lease obligations |  | Other liabilities |  | $ | 32,149 |  |  | $ | 32,763 |
Summary of Lease Costs and Other Lease Information | The following table represents lease costs and other lease information (in thousands):
|  | Three months ended September 30, |  |  | Nine months ended September 30, |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Lease costs: |  |  |  |  |  |  |  |  |  |  |  |
Operating lease costs |  | $ | 779 |  |  | $ | 775 |  |  | $ | 2,338 |  |  | $ | 2,327 |
Variable lease costs (1) |  |  | 159 |  |  |  | 139 |  |  |  | 386 |  |  |  | 334 |
Sublease income |  |  | (35 | ) |  |  | (36 | ) |  |  | (104 | ) |  |  | (103 | )
Net lease costs |  | $ | 903 |  |  | $ | 878 |  |  | $ | 2,620 |  |  | $ | 2,558 |
Other information: |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for amounts included in the measurement of lease liabilities: |  |  |  |  |  |  |  |  |  |  |  |
Operating cash flows from operating leases |  | $ | 754 |  |  | $ | 775 |  |  | $ | 2,266 |  |  | $ | 2,327 |
Right of use assets obtained in exchange for new operating lease liabilities |  | $ | 392 |  |  | $ | 139 |  |  | $ | 703 |  |  | $ | 334 |
(1) Variable lease costs primarily represent variable payments such as common area maintenance, insurance, taxes and utilities.
Summary of Future Minimum Payments Under Non-cancellable Operating Leases | Future minimum payments under non-cancellable operating leases with initial or remaining terms of one year or more, are as follows at September 30, 2025 (in thousands):
Twelve months ended September 30, |  |
2025 | $ | 751 |
2026 |  | 2,931 |
2027 |  | 2,904 |
2028 |  | 2,619 |
2029 |  | 2,317 |
Thereafter |  | 35,161 |
Total future minimum operating lease payments |  | 46,683 |
Amounts representing interest |  | (14,534 | )
Present value of net future minimum operating lease payments | $ | 32,149 |

X
- Definition Schedule of classification of right of use assets and lease liabilities. + References No definition available. + Details
Name: | fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock
Namespace Prefix: | fisi_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Schedule of lease costs and other lease information. + References No definition available. + Details
Name: | fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock
Namespace Prefix: | fisi_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_LeasesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of undiscounted cash flows of lessee's operating lease liability. Includes, but is not limited to, reconciliation of undiscounted cash flows to operating lease liability recognized in statement of financial position. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-6 + Details
Name: | us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration