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Loans Held For Sale And Loan Servicing Rights (Activity In Capitalized Mortgage Serving Assets) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Loans Held For Sale And Loan Servicing Rights [Abstract] |  |  |
Mortgage servicing assets, beginning of year | $ 1,479 fisi_MortgageServicingAssetsBeforeValuationAllowance | $ 1,637 fisi_MortgageServicingAssetsBeforeValuationAllowance | $ 1,609 fisi_MortgageServicingAssetsBeforeValuationAllowance
Originations | 172 us-gaap_ServicingAssetAtFairValueAdditions | 277 us-gaap_ServicingAssetAtFairValueAdditions | 554 us-gaap_ServicingAssetAtFairValueAdditions
Amortization | (316)us-gaap_AmortizationOfMortgageServicingRightsMSRs | (435)us-gaap_AmortizationOfMortgageServicingRightsMSRs | (526)us-gaap_AmortizationOfMortgageServicingRightsMSRs
Mortgage servicing assets, end of year | 1,335 fisi_MortgageServicingAssetsBeforeValuationAllowance | 1,479 fisi_MortgageServicingAssetsBeforeValuationAllowance | 1,637 fisi_MortgageServicingAssetsBeforeValuationAllowance
Valuation allowance | (6)fisi_MortgageServicingAssetsValuationAllowance | (3)fisi_MortgageServicingAssetsValuationAllowance | (168)fisi_MortgageServicingAssetsValuationAllowance
Mortgage servicing assets, net, end of year | $ 1,329 fisi_MortgageServicingAssetsNetOfValuationAllowance | $ 1,476 fisi_MortgageServicingAssetsNetOfValuationAllowance | $ 1,469 fisi_MortgageServicingAssetsNetOfValuationAllowance

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- Details
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- Definition Mortgage Servicing Assets, Before Valuation Allowance + References No definition available. + Details
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- Definition Mortgage Servicing Assets Net Of Valuation Allowance + References No definition available. + Details
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- Definition Mortgage Servicing Assets, Valuation Allowance + References No definition available. + Details
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- Definition The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122739-111746 + Details
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- Definition The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746 + Details
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