XML 51 R40.htm IDEA: XBRL DOCUMENT
v3.5.0.2

Investment Securities (Narrative) (Details) $ in Thousands | Jun. 30, 2016 USD ($) security | Dec. 31, 2015 USD ($) security
--- | --- | ---
Investment Securities [Abstract] |  |
Securities pledged as collateral | $ 856,500 |
Number of security positions, unrealized loss position | security | 29 | 174
Number of security positions, unrealized loss position for more than 12 months | security | 6 | 14
Securities, 12 months or longer, Fair Value | $ 3,272 | $ 35,864
Securities, 12 months or longer, Unrealized Losses | $ 8 | $ 513
Number of security positions, unrealized loss position for less than 12 months | security | 23 | 160
Securities, less than 12 months, Fair Value | $ 21,523 | $ 400,299
Securities, less than 12 months, Unrealized Losses | $ 37 | $ 5,593

X
- Definition Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for less than twelve months. + References No definition available. + Details
Name: | fisi_AvailableForSaleSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions
Namespace Prefix: | fisi_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for twelve months or longer. + References No definition available. + Details
Name: | fisi_AvailableForSaleSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions
Namespace Prefix: | fisi_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of accumulated pre-tax unrealized loss on securities that have been in a loss position for twelve months or longer. + References No definition available. + Details
Name: | fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of accumulated pre-tax unrealized loss on investments in securities that have been in a loss position for less than twelve months. + References No definition available. + Details
Name: | fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This item represents the fair value of securities that have been in a continuous unrealized loss position for less than twelve months. + References No definition available. + Details
Name: | fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the fair value of securities that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
Name: | fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | fisi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The fair value of available-for-sale securities that serve as collateral for borrowings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5086-111524 + Details
Name: | us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration