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Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical) (USD $) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Common stock dividends per share, declared | $ 0.20us-gaap_CommonStockDividendsPerShareDeclared | $ 0.19us-gaap_CommonStockDividendsPerShareDeclared
Series A 3% Preferred Stock [Member] |  |
Preferred stock dividends per share, declared | $ 0.75us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = fisi_Series3PreferredStockMember | $ 0.75us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = fisi_Series3PreferredStockMember
Preferred stock, dividend percentage | 3.00%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = fisi_Series3PreferredStockMember | 3.00%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = fisi_Series3PreferredStockMember
Series B-1 8.48% Preferred Stock [Member] |  |
Preferred stock dividends per share, declared | $ 2.12us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesBPreferredStockMember | $ 2.12us-gaap_PreferredStockDividendsPerShareDeclared / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesBPreferredStockMember
Preferred stock, dividend percentage | 8.48%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesBPreferredStockMember | 8.48%us-gaap_PreferredStockDividendRatePercentage / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesBPreferredStockMember

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition The percentage rate used to calculate dividend payments on preferred stock. + References No definition available. + Details
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- Definition Aggregate dividends declared during the period for each share of preferred stock outstanding. + References No definition available. + Details
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- Details
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- Details
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