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Business Combinations (Goodwill And Other Intangible Assets Acquired) (Details) $ in Thousands	Jan. 05, 2016 USD ($)
Customer Relationships [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Other Intangible Assets [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Courier Capital [Member]
Goodwill	$ 6,015
Goodwill and other intangible assets acquired	9,943
Courier Capital [Member] | Customer Relationships [Member]
Other intangible assets	3,900
Courier Capital [Member] | Other Intangible Assets [Member]
Other intangible assets	$ 28

X

- Definition

Goodwill and Other Intangible Assets Acquired

+ References

No definition available.

+ Details

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Namespace Prefix:	fisi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275

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- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, resulting from a business combination.

+ References

No definition available.

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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- Details

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