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v2.4.1.9

Segment Reporting (Business Segment Assets) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2014 segment | Dec. 31, 2013 | Dec. 31, 2012
Segment Reporting Information [Line Items] |  |  |  |
Goodwill | $ 61,153 us-gaap_Goodwill |  | $ 48,536 us-gaap_Goodwill | $ 48,536 us-gaap_Goodwill
Other intangible assets, net | 7,486 us-gaap_FiniteLivedIntangibleAssetsNet |  |  |
Assets | 3,089,521 us-gaap_Assets | [1] | 2,928,636 us-gaap_Assets |
Number of operating segments | 2 us-gaap_NumberOfOperatingSegments |  |  |
Banking [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Goodwill | 48,536 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = fisi_BankingSegmentMember |  |  |
Other intangible assets, net | 1,125 us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_StatementBusinessSegmentsAxis = fisi_BankingSegmentMember |  |  |
Assets | 3,065,109 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = fisi_BankingSegmentMember | [1] |  |
Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Goodwill | 12,617 us-gaap_Goodwill / us-gaap_StatementBusinessSegmentsAxis = fisi_InsuranceSegmentMember |  |  |
Other intangible assets, net | 6,361 us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_StatementBusinessSegmentsAxis = fisi_InsuranceSegmentMember |  |  |
Assets | 20,368 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = fisi_InsuranceSegmentMember | [1] |  |
Holding Company and Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Assets | $ 4,044 us-gaap_Assets / us-gaap_StatementBusinessSegmentsAxis = fisi_HoldingCompanyAndOtherSegmentMember | [1] |  |
[1] | Reflects activity from SDN since August 1, 2014, the date of acquisition.

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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.18) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 18 -Article 5 + Details
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- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 + Details
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
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