XML 63 R50.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014
Significant Accounting Policies [Line Items] |  |
Days past due when loans are generally placed on nonaccrual status, in days | 90 days |
Days past due when loans are generally charged-off in full, in days | 120 days |
General period after loans become current, accrual status returned, in months | 6 months |
Other real estate owned | $ 163 | $ 194
Number of consecutive years used for compensation calculation | 5 years |
FHLB stock | $ 15,100 | 15,100
FRB stock | 4,900 | 3,900
Equity method investments, asset amount | $ 5,000 | $ 4,900
Minimum [Member] |  |
Significant Accounting Policies [Line Items] |  |
Standby letters of credit outstanding original term, in years | 1 year |
Loss rate look-back period | 24 months |
Loss emergence period | 12 months |
Minimum [Member] | Building And Building Improvements [Member] |  |
Significant Accounting Policies [Line Items] |  |
Premise and equipment, estimated useful lives, in years | 15 years |
Minimum [Member] | Software Furniture And Equipment [Member] |  |
Significant Accounting Policies [Line Items] |  |
Premise and equipment, estimated useful lives, in years | 3 years |
Maximum [Member] |  |
Significant Accounting Policies [Line Items] |  |
Standby letters of credit outstanding original term, in years | 5 years |
Loss rate look-back period | 48 months |
Loss emergence period | 24 months |
Maximum [Member] | Building And Building Improvements [Member] |  |
Significant Accounting Policies [Line Items] |  |
Premise and equipment, estimated useful lives, in years | 39 years |
Maximum [Member] | Software Furniture And Equipment [Member] |  |
Significant Accounting Policies [Line Items] |  |
Premise and equipment, estimated useful lives, in years | 10 years |
Other Intangible Assets [Member] |  |
Significant Accounting Policies [Line Items] |  |
Estimated average life | 20 years |
Core Deposits [Member] |  |
Significant Accounting Policies [Line Items] |  |
Estimated average life | 9 years 6 months |

X
- Definition Days Past Due When Loans Are Generally Charged-Off In Full, In Days + References No definition available. + Details
Name: | fisi_DaysPastDueWhenLoansAreGenerallyChargedOffInFullInDays
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Days Past Due When Loans Are Generally Placed On Nonaccrual Status, In Days + References No definition available. + Details
Name: | fisi_DaysPastDueWhenLoansAreGenerallyPlacedOnNonaccrualStatusInDays
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Debt Outstanding Original Term, In Years + References No definition available. + Details
Name: | fisi_DebtOutstandingOriginalTermInYears
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition General Period After Loans Become Current, Accrual Status Returned, In Months + References No definition available. + Details
Name: | fisi_GeneralPeriodAfterLoansBecomeCurrentAccrualStatusReturnedInMonths
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loss Emergence Period + References No definition available. + Details
Name: | fisi_LossEmergencePeriod
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loss Rate Look-Back Period + References No definition available. + Details
Name: | fisi_LossRateLookBackPeriod
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Years Used for Compensation Calculation + References No definition available. + Details
Name: | fisi_NumberOfYearsUsedForCompensationCalculation
Namespace Prefix: | fisi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Significant Accounting Policies [Line Items] + References No definition available. + Details
Name: | fisi_SignificantAccountingPoliciesLineItems
Namespace Prefix: | fisi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of assets reported by an equity method investment of the entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(g)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33912-111571 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph w -Article 1 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph bb -Article 1 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph g -Subparagraph 1, 2 -Article 4 + Details
Name: | us-gaap_EquityMethodInvestmentSummarizedFinancialInformationAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809 + Details
Name: | us-gaap_FederalHomeLoanBankStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809 + Details
Name: | us-gaap_FederalReserveBankStock
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10(4)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_OtherRealEstate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=fisi_SoftwareFurnitureAndEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OtherIntangibleAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |