XML 19 R7.htm IDEA: XBRL DOCUMENT v3.25.0.1

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Common stock dividends per share, declared	$ 1.2	$ 1.2	$ 1.16
Series A 3% Preferred Stock [Member]
Preferred stock, dividend percentage	3.00%	3.00%	3.00%
Preferred stock dividends per share, declared	$ 3	$ 3	$ 3
Series B-1 8.48% Preferred Stock [Member]
Preferred stock, dividend percentage	8.48%	8.48%	8.48%
Preferred stock dividends per share, declared	$ 8.48	$ 8.48	$ 8.48

X

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

+ Details

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-12A(Column A)(Footnote 3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12(Column A)(Footnote 4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Column A)(Footnote 3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-3

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14(Column A)(Footnote 3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-6

+ Details

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Aggregate dividends declared during the period for each share of preferred stock outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=fisi_SeriesAThreePercentagePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: