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Commitments And Contingencies (Narrative) (Details) (USD $) | Jun. 30, 2014 | Dec. 31, 2013
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Commitments And Contingencies [Abstract] |  |
Forward sales commitments | $ 393,000 | $ 0

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- Definition Commitments to sell residential real estate loans. + References No definition available. + Details
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Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration