XML 44 R37.htm IDEA: XBRL DOCUMENT
v3.25.3

Share-Based Compensation Plans (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2025
Share-Based Payment Arrangement, Noncash Expense [Abstract] |
Summary of Restricted Stock Awards ,Restricted Stock Unit Award and Performance Share Units Activity | The Company granted restricted stock awards (“RSAs”), restricted stock unit award (“RSUs”), and performance-based restricted stock units (“PSUs”) during the nine months ended September 30, 2025 as follows:
|  | Number of Underlying Shares |  |  | Weighted Average Grant Date Fair Value |
RSAs |  |  | 15,638 |  |  | $ | 25.35 |
RSUs |  |  | 205,579 |  |  | $ | 23.21 |
PSUs |  |  | 42,232 |  |  | $ | 23.27 |
Share-Based Compensation Expense and The Total Income Tax Benefit Included In Consolidated Statements of Operations | The share-based compensation expense included in the consolidated statements of operations, is as follows (in thousands):
|  | Three months ended September 30, |  |  | Nine months ended September 30, |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Salaries and employee benefits |  | $ | 708 |  |  | $ | 450 |  |  | $ | 1,874 |  |  | $ | 1,485 |
Other noninterest expense |  |  | 48 |  |  |  | 44 |  |  |  | 342 |  |  |  | 324 |
Total share-based compensation expense |  | $ | 756 |  |  | $ | 494 |  |  | $ | 2,216 |  |  | $ | 1,809 |
Income tax benefit realized for compensation costs |  | $ | 112 |  |  | $ | 18 |  |  | $ | 485 |  |  | $ | 401 |

X
- Definition Schedule of Share-based Compensation, Restricted Stock Units and Performance Share Units Activity [Table Text Block] + References No definition available. + Details
Name: | fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock
Namespace Prefix: | fisi_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
Name: | us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

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