XML 54 R36.htm IDEA: XBRL DOCUMENT v2.4.1.9
Business Combinations (Narrative) (Details) (USD $)
0 Months Ended 3 Months Ended
Aug. 01, 2014
Mar. 31, 2015
Apr. 15, 2015
Scott Danahy Naylon Co., Inc. [Member]      
Significant Acquisitions and Disposals [Line Items]      
Consideration including both cash and stock $ 16,900,000us-gaap_BusinessCombinationConsiderationTransferredIncludingEquityInterestInAcquireeHeldPriorToCombination1
/ us-gaap_BusinessAcquisitionAxis
= fisi_ScottDanahyNaylonCo.Inc.Member
   
Contingent future payments 3,400,000us-gaap_BusinessCombinationContingentConsiderationLiability
/ us-gaap_BusinessAcquisitionAxis
= fisi_ScottDanahyNaylonCo.Inc.Member
   
Estimated Fair Value Measurement Period, Number Of Years   1 year  
Contingent consideration 3,227,000us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred
/ us-gaap_BusinessAcquisitionAxis
= fisi_ScottDanahyNaylonCo.Inc.Member
   
Identified intangible assets 6,640,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill
/ us-gaap_BusinessAcquisitionAxis
= fisi_ScottDanahyNaylonCo.Inc.Member
   
Goodwill resulting from acquisition 12,617,000us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_BusinessAcquisitionAxis
= fisi_ScottDanahyNaylonCo.Inc.Member
   
Subsequent Event [Member]      
Significant Acquisitions and Disposals [Line Items]      
Principal amount     $ 40,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember