$FISI
FINANCIAL INSTITUTIONS INC Stock $fisi

$fisi Overview Financials Valuation SEC Filings Company Website

2018 Q4 Form 10-K Financial Statement

#000156459020008690 Filed on March 04, 2020

Income Statement

Concept	2018 Q4	2018	2017 Q4
Revenue		$152.7M
YoY Change		17.39%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$1.620M	$6.480M	$1.570M
YoY Change	3.18%	4.85%	6.08%
% of Gross Profit
Operating Expenses
YoY Change
Operating Profit
YoY Change
Interest Expense		$29.87M
YoY Change		70.72%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$9.690M	$49.53M	$11.64M
YoY Change	-16.75%	13.94%	-0.85%
Income Tax	$2.200M	$10.01M	$3.480M
% Of Pretax Income	22.7%	20.2%	29.9%
Net Earnings	$7.490M	$39.53M	$11.06M
YoY Change	-32.28%	17.9%	27.27%
Net Earnings / Revenue		25.88%
Basic Earnings Per Share		$2.39
Diluted Earnings Per Share	$469.0K	$2.39	$700.0K
COMMON SHARES
Basic Shares Outstanding	15.92M	15.91M
Diluted Shares Outstanding		15.96M

Balance Sheet

Concept	2018 Q4	2018	2017 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$102.8M		$99.20M
Short-Term Investments
Other Short-Term Assets
YoY Change
Inventory
Prepaid Expenses
Receivables
Other Receivables
Total Short-Term Assets
YoY Change
LONG-TERM ASSETS
Property, Plant & Equipment	$42.84M	$42.80M	$45.19M
YoY Change	-5.2%	-5.31%	6.58%
Goodwill	$66.06M		$65.84M
YoY Change	0.34%		-0.87%
Intangibles
YoY Change
Long-Term Investments
YoY Change
Other Assets		$7.900M
YoY Change		-236.21%
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$4.312B	$4.312B	$4.105B
YoY Change	5.03%	5.03%	10.64%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable
YoY Change
Accrued Expenses
YoY Change
Deferred Revenue
YoY Change
Short-Term Debt	$469.5M	$64.00M	$446.2M
YoY Change	5.22%		34.6%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$64.00M	$64.00M
YoY Change
LONG-TERM LIABILITIES
Long-Term Debt	$39.20M	$39.20M	$39.10M
YoY Change	0.26%	0.26%	0.0%
Other Long-Term Liabilities	$39.80M	$39.80M	$28.50M
YoY Change	39.65%	39.65%	16.33%
Total Long-Term Liabilities	$79.00M	$79.00M	$67.60M
YoY Change	16.86%	16.86%	6.29%
TOTAL LIABILITIES
Total Short-Term Liabilities	$64.00M	$64.00M
Total Long-Term Liabilities	$79.00M	$79.00M	$67.60M
Total Liabilities	$3.915B	$3.915B	$3.724B
YoY Change	5.14%	5.14%	9.84%
SHAREHOLDERS EQUITY
Retained Earnings	$279.9M		$257.1M
YoY Change	8.86%
Common Stock	$161.0K		$161.0K
YoY Change	0.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$2.486M		$2.533M
YoY Change	-1.86%
Treasury Stock Shares	$127.6K		$131.2K
Shareholders Equity	$396.3M	$396.3M	$381.2M
YoY Change
Total Liabilities & Shareholders Equity	$4.312B	$4.312B	$4.105B
YoY Change	5.03%	5.03%	10.64%

Cashflow Statement

Concept	2018 Q4	2018	2017 Q4
OPERATING ACTIVITIES
Net Income	$7.490M	$39.53M	$11.06M
YoY Change	-32.28%	17.9%	27.27%
Depreciation, Depletion And Amortization	$1.620M	$6.480M	$1.570M
YoY Change	3.18%	4.85%	6.08%
Cash From Operating Activities	$14.33M	$65.14M	$10.87M
YoY Change	31.83%	40.75%	17.26%
INVESTING ACTIVITIES
Capital Expenditures	-$840.0K	$2.842M	-$770.0K
YoY Change	9.09%	-63.28%	-77.22%
Acquisitions		$4.447M
YoY Change		557.84%
Other Investing Activities	-$66.36M	-$590.0K	-$77.80M
YoY Change	-14.7%	152.14%	3.16%
Cash From Investing Activities	-$67.20M	-$225.4M	-$78.57M
YoY Change	-14.47%	-39.51%	-0.29%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net		$113.0K	$38.30M
YoY Change		-100.3%
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	38.29M	163.8M	69.06M
YoY Change	-44.56%	-53.75%	129.59%
NET CHANGE
Cash From Operating Activities	14.33M	65.14M	10.87M
Cash From Investing Activities	-67.20M	-225.4M	-78.57M
Cash From Financing Activities	38.29M	163.8M	69.06M
Net Change In Cash	-14.58M	3.560M	1.360M
YoY Change	-1172.06%	-87.25%	-103.45%
FREE CASH FLOW
Cash From Operating Activities	$14.33M	$65.14M	$10.87M
Capital Expenditures	-$840.0K	$2.842M	-$770.0K
Free Cash Flow	$15.17M	$62.30M	$11.64M
YoY Change	30.33%	61.65%	-7.98%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value
CY2019	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2019
CY2019	dei	Document Type DocumentType	10-K
CY2019	dei	Amendment Flag AmendmentFlag	false
CY2019	dei	Document Period End Date DocumentPeriodEndDate	2019-12-31
CY2018	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	152732000
CY2017	us-gaap	Interest And Other Income InterestAndOtherIncome	73000
CY2019	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	168800000
CY2019	dei	Security12b Title Security12bTitle	Common stock, par value $0.01 per share
CY2019Q2	dei	Entity Public Float EntityPublicFloat	457230000
CY2019Q4	us-gaap	Cash And Due From Banks CashAndDueFromBanks	112947000
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	417917000
CY2018Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	445677000
CY2019Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	359000000
CY2018Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	446581000
CY2019Q4	us-gaap	Loans Receivable Held For Sale Net Not Part Of Disposal Group LoansReceivableHeldForSaleNetNotPartOfDisposalGroup	4224000
CY2018Q4	us-gaap	Loans Receivable Held For Sale Net Not Part Of Disposal Group LoansReceivableHeldForSaleNetNotPartOfDisposalGroup	2868000
CY2019Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	3190505000
CY2019Q4	us-gaap	Bank Owned Life Insurance BankOwnedLifeInsurance	68942000
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	41424000
CY2019Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	74923000
CY2019Q4	us-gaap	Other Assets OtherAssets	114296000
CY2019Q4	us-gaap	Assets Assets	4384178000
CY2019Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	707752000
CY2019Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	627842000
CY2019Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1039892000
CY2019Q4	us-gaap	Time Deposits TimeDeposits	1180189000
CY2019Q4	us-gaap	Deposits Deposits	3555675000
CY2019Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	275500000
CY2019Q4	us-gaap	Long Term Debt LongTermDebt	39273000
CY2019Q4	us-gaap	Other Liabilities OtherLiabilities	74783000
CY2019Q4	us-gaap	Liabilities Liabilities	3945231000
CY2019Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies
CY2019Q4	us-gaap	Preferred Stock Value PreferredStockValue	17328000
CY2019Q4	us-gaap	Common Stock Value CommonStockValue	161000
CY2019Q4	us-gaap	Additional Paid In Capital AdditionalPaidInCapital	124582000
CY2019	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	No
CY2019	dei	Entity Central Index Key EntityCentralIndexKey	0000862831
CY2019	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2019	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2019	dei	Entity Filer Category EntityFilerCategory	Accelerated Filer
CY2019	dei	Entity Small Business EntitySmallBusiness	false
CY2019	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2019	dei	Entity Shell Company EntityShellCompany	false
CY2019	dei	Entity File Number EntityFileNumber	000-26481
CY2019	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	16-0816610
CY2019	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	NY
CY2019	dei	Entity Address Address Line1 EntityAddressAddressLine1	220 LIBERTY STREET
CY2019	dei	Entity Address City Or Town EntityAddressCityOrTown	WARSAW
CY2019	dei	Entity Address State Or Province EntityAddressStateOrProvince	NY
CY2019	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	14569
CY2019	dei	City Area Code CityAreaCode	585
CY2019	dei	Local Phone Number LocalPhoneNumber	786-1100
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CY2019	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2019	dei	Document Annual Report DocumentAnnualReport	true
CY2019	dei	Document Transition Report DocumentTransitionReport	false
CY2019	dei	Security Exchange Name SecurityExchangeName	NASDAQ
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CY2018Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies
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CY2017	us-gaap	Interest Expense Long Term Debt InterestExpenseLongTermDebt	2471000
CY2017	us-gaap	Interest Expense InterestExpense	17495000
CY2019	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2019	dei	Entity Registrant Name EntityRegistrantName	FINANCIAL INSTITUTIONS INC
CY2019	dei	Trading Symbol TradingSymbol	FISI
CY2019	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2019	us-gaap	Interest And Dividend Income Securities InterestAndDividendIncomeSecurities	18532000
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CY2019	us-gaap	Interest And Fee Income Loans And Leases InterestAndFeeIncomeLoansAndLeases	149873000
CY2019	us-gaap	Interest And Other Income InterestAndOtherIncome	395000
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CY2018Q4	us-gaap	Bank Owned Life Insurance BankOwnedLifeInsurance	67116000
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	42839000
CY2018Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	76173000
CY2018Q4	us-gaap	Other Assets OtherAssets	75005000
CY2018Q4	us-gaap	Assets Assets	4311698000
CY2018Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	755460000
CY2018Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	622482000
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CY2018Q4	us-gaap	Deposits Deposits	3366907000
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CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-21281000
CY2018Q4	us-gaap	Treasury Stock Value TreasuryStockValue	2486000
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	396293000
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CY2019Q4	fisi	Investment Securities In Unrealized Loss Positions Less Than Twelve Months Qualitative Disclosure Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions	57
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CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	363259000
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CY2019	us-gaap	Interest Expense InterestExpense	38888000
CY2018	us-gaap	Interest Expense InterestExpense	29868000
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CY2019	fisi	Noninterest Income Loan Servicing NoninterestIncomeLoanServicing	432000
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CY2018	fisi	Noninterest Income Service Charges On Deposits NoninterestIncomeServiceChargesOnDeposits	7120000
CY2019	fisi	Noninterest Income Service Charges On Deposits NoninterestIncomeServiceChargesOnDeposits	7241000
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CY2018	us-gaap	Insurance Services Revenue InsuranceServicesRevenue	4930000
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CY2017	fisi	Atm And Debit Card AtmAndDebitCard	5721000
CY2017	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	4914000
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CY2019	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1005000
CY2018	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1975000
CY2019	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	3577000
CY2018	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	3582000
CY2017	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2171000
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	1250000
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	1257000
CY2017	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	1170000
CY2018	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	2350000
CY2017	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	1575000
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	9671000
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	8665000
CY2017	us-gaap	Other Noninterest Expense OtherNoninterestExpense	7791000
CY2019	us-gaap	Noninterest Expense NoninterestExpense	102828000
CY2018	us-gaap	Noninterest Expense NoninterestExpense	100876000
CY2017	us-gaap	Noninterest Expense NoninterestExpense	90513000
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	59421000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	49532000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	43471000
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	10559000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	10006000
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9945000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	48862000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	39526000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	33526000
CY2019	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	1461000
CY2018	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	1461000
CY2017	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	1462000
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	47401000
CY2018	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	38065000
CY2017	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	32064000
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.97
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.39
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.13
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.96
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.39
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.13
CY2019	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.00
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.96
CY2017	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.85
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	15972000
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	15910000
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	15044000
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	16031000
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	15956000
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	15085000
CY2019	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	9323000
CY2018	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	-4494000
CY2017	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	454000
CY2019	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss After Reclassification And Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax	-242000
CY2018	us-gaap	Other Comprehensive Income Loss Cash Flow Hedge Gain Loss After Reclassification And Tax OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax	-276000
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-470000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	4595000
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1581000
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	9551000
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-9365000
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	2035000
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	58413000
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	30161000
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	35561000
CY2016Q4	us-gaap	Stockholders Equity StockholdersEquity	320054000
CY2017	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	38303000
CY2017	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	148000
CY2017	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	1174000
CY2017	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	413000
CY2017	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	243000
CY2017	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	12952000
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	381177000
CY2018	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	113000
CY2018	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	1301000
CY2018	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	320000
CY2018	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	185000
CY2018	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	15276000
CY2018Q4	us-gaap	Cumulative Effect Of New Accounting Principle In Period Of Adoption CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	-710000
CY2018Q4	fisi	Stockholders Equity Adjusted Balance StockholdersEquityAdjustedBalance	395583000
CY2019	us-gaap	Stock Issued During Period Value New Issues StockIssuedDuringPeriodValueNewIssues	1151000
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	293000
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	1406000
CY2019	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	125000
CY2019	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	15977000
CY2019	us-gaap	Profit Loss ProfitLoss	48862000
CY2018	us-gaap	Profit Loss ProfitLoss	39526000
CY2017	us-gaap	Profit Loss ProfitLoss	33526000
CY2019	us-gaap	Depreciation And Amortization DepreciationAndAmortization	8213000
CY2018	us-gaap	Depreciation And Amortization DepreciationAndAmortization	6477000
CY2017	us-gaap	Depreciation And Amortization DepreciationAndAmortization	6177000
CY2019	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-2069000
CY2018	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-2456000
CY2017	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-3298000
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	1406000
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	1301000
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	1174000
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	369000
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-10480000
CY2017	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	12403000
CY2019	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	41479000
CY2018	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	30547000
CY2017	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	14555000
CY2019	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	41626000
CY2018	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	29901000
CY2017	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	15847000
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	21263000
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-13376000
CY2017	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	24505000
CY2019	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	14973000
CY2018	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	3065000
CY2017	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	4016000
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	57710000
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	65139000
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	46279000
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	195660000
CY2018	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	44919000
CY2017	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	86434000
CY2019	us-gaap	Payments To Acquire Held To Maturity Securities PaymentsToAcquireHeldToMaturitySecurities	23494000
CY2018	us-gaap	Payments To Acquire Held To Maturity Securities PaymentsToAcquireHeldToMaturitySecurities	28017000
CY2017	us-gaap	Payments To Acquire Held To Maturity Securities PaymentsToAcquireHeldToMaturitySecurities	71479000
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	82358000
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	90114000
CY2017	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	51978000
CY2019	us-gaap	Proceeds From Sale And Maturity Of Held To Maturity Securities ProceedsFromSaleAndMaturityOfHeldToMaturitySecurities	83508000
CY2018	us-gaap	Proceeds From Sale And Maturity Of Held To Maturity Securities ProceedsFromSaleAndMaturityOfHeldToMaturitySecurities	96211000
CY2017	us-gaap	Proceeds From Sale And Maturity Of Held To Maturity Securities ProceedsFromSaleAndMaturityOfHeldToMaturitySecurities	96376000
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	178059000
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	29851000
CY2017	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	50084000
CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	167234000
CY2018	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	361915000
CY2017	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	404905000
CY2019	fisi	Proceeds From Loans Sold To Others ProceedsFromLoansSoldToOthers	21077000
CY2019	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	68000
CY2018	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	35000
CY2017	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	52000
CY2019	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-360000
CY2018	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-590000
CY2017	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	-234000
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	3639000
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	2842000
CY2017	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	7740000
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	4447000
CY2017	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	676000
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-24733000
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-225409000
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-372614000
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	188768000
CY2018	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	156733000
CY2017	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	214952000
CY2019	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	-194000000
CY2018	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	23300000
CY2017	us-gaap	Proceeds From Repayments Of Short Term Debt ProceedsFromRepaymentsOfShortTermDebt	114700000
CY2018	us-gaap	Payments For Repurchase Of Preferred Stock And Preference Stock PaymentsForRepurchaseOfPreferredStockAndPreferenceStock	1000
CY2017	us-gaap	Payments For Repurchase Of Preferred Stock And Preference Stock PaymentsForRepurchaseOfPreferredStockAndPreferenceStock	9000
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	38303000
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	293000
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	113000
CY2017	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	148000
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	320000
CY2017	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	413000
CY2019	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	1461000
CY2018	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	1462000
CY2017	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	1462000
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	15799000
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	14947000
CY2017	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	12496000
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-22785000
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	163830000
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	22800000
CY2019Q4	us-gaap	Operating Lease Liability Statement Of Financial Position Extensible List OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList	us-gaap:OtherLiabilities
CY2018Q4	us-gaap	Operating Lease Liability Statement Of Financial Position Extensible List OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList	us-gaap:OtherLiabilities
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P21Y8M12D
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	354253000
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	10192000
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	3560000
CY2017	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	27918000
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	102755000
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	99195000
CY2016Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	71277000
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Including Disposal Group And Discontinued Operations CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	112947000
CY2019	us-gaap	Interest Income Securities Taxable InterestIncomeSecuritiesTaxable	14382000
CY2019	us-gaap	Interest Income Securities Tax Exempt InterestIncomeSecuritiesTaxExempt	4150000
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	2391000
CY2019	us-gaap	Use Of Estimates UseOfEstimates	<p style="text-align:justify;margin-bottom:0pt;margin-top:12pt;margin-left:3.33%;text-indent:0%;font-weight:bold;font-style:italic;font-size:10pt;font-family:Times New Roman;text-transform:none;font-variant: normal;">(b.) Use of Estimates</p> <p style="text-align:justify;margin-bottom:0pt;margin-top:6pt;margin-left:3.33%;text-indent:0%;font-size:10pt;font-family:Times New Roman;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">In preparing the consolidated financial statements in conformity with GAAP, management is required to make estimates and assumptions that affect the reported amount of assets and liabilities as of the date of the statement of financial condition and reported amounts of revenue and expenses during the reporting period. Material estimates relate to the determination of the allowance for loan losses, the carrying value of goodwill and deferred tax assets, and assumptions used in the defined benefit pension plan accounting. These estimates and assumptions are based on management’s best estimates and judgment and are evaluated on an ongoing basis using historical experience and other factors, including the current economic environment. The Company adjusts these estimates and assumptions when facts and circumstances dictate. As future events cannot be determined with precision, actual results could differ significantly from the Company’s estimates.</p>
CY2019	us-gaap	Prior Period Reclassification Adjustment Description PriorPeriodReclassificationAdjustmentDescription	<p style="text-align:justify;margin-bottom:0pt;margin-top:12pt;margin-left:3.33%;text-indent:0%;font-weight:bold;font-style:italic;font-size:10pt;font-family:Times New Roman;text-transform:none;font-variant: normal;">(x.) Reclassifications</p> <p style="text-align:justify;margin-bottom:0pt;margin-top:6pt;margin-left:3.33%;text-indent:0%;font-size:10pt;font-family:Times New Roman;font-weight:normal;font-style:normal;text-transform:none;font-variant: normal;">Certain items in prior financial statements have been reclassified to conform to the current presentation. These reclassifications did not result in any changes to previously reported net income or shareholders’ equity.</p>
CY2018Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	3044320000
CY2019	us-gaap	Interest Paid Net InterestPaidNet	37225000
CY2018	us-gaap	Interest Paid Net InterestPaidNet	28626000
CY2017	us-gaap	Interest Paid Net InterestPaidNet	14850000
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	9853000
CY2018	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	3527000
CY2017	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	13187000
CY2019	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	557000
CY2018	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	642000
CY2017	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	426000
CY2019Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	4365000
CY2018Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	4187000
CY2017Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	3859000
CY2019	fisi	Decrease Increase In Net Unsettled Security Purchases DecreaseIncreaseInNetUnsettledSecurityPurchases	-2650000
CY2018	fisi	Decrease Increase In Net Unsettled Security Purchases DecreaseIncreaseInNetUnsettledSecurityPurchases	2650000
CY2019	fisi	Securities Transferred From Available For Sale To Held To Maturity To Available For Sale At Cost SecuritiesTransferredFromAvailableForSaleToHeldToMaturityToAvailableForSaleAtCost	26175000
CY2019	us-gaap	Stock Issued1 StockIssued1	1151000
CY2018	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	2561000
CY2017	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	812000
CY2018	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	128000
CY2017	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	44000
CY2019	fisi	Days Past Due When Loans Are Generally Charged Off In Full In Days DaysPastDueWhenLoansAreGenerallyChargedOffInFullInDays	P120D
CY2019Q4	us-gaap	Other Real Estate OtherRealEstate	468000
CY2018Q4	us-gaap	Other Real Estate OtherRealEstate	230000
CY2019Q4	us-gaap	Federal Home Loan Bank Stock FederalHomeLoanBankStock	14600000
CY2018Q4	us-gaap	Federal Home Loan Bank Stock FederalHomeLoanBankStock	20300000
CY2019Q4	us-gaap	Federal Reserve Bank Stock FederalReserveBankStock	6100000
CY2018Q4	us-gaap	Federal Reserve Bank Stock FederalReserveBankStock	6100000
CY2019Q4	us-gaap	Equity Method Investment Summarized Financial Information Assets EquityMethodInvestmentSummarizedFinancialInformationAssets	7600000
CY2018Q4	us-gaap	Equity Method Investment Summarized Financial Information Assets EquityMethodInvestmentSummarizedFinancialInformationAssets	6000000
CY2019	fisi	Number Of Years Used For Compensation Calculation NumberOfYearsUsedForCompensationCalculation	P5Y
CY2019Q1	us-gaap	Tax Cuts And Jobs Act Of2017 Reclassification From Aoci To Retained Earnings Tax Effect TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect	2800000
CY2019Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	415852000
CY2018Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	455582000
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	3696000
CY2018Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	845000
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	1631000
CY2018Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	10750000
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	4882000
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	623000
CY2018Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	899000
CY2018Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	7899000
CY2019Q4	fisi	Debt Securities Available For Sale And Held To Maturity Restricted DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted	676900000
CY2018Q4	fisi	Debt Securities Available For Sale And Held To Maturity Restricted DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted	751000000
CY2018	us-gaap	Interest Income Securities Taxable InterestIncomeSecuritiesTaxable	16510000
CY2017	us-gaap	Interest Income Securities Taxable InterestIncomeSecuritiesTaxable	17886000
CY2018	us-gaap	Interest Income Securities Tax Exempt InterestIncomeSecuritiesTaxExempt	5091000
CY2017	us-gaap	Interest Income Securities Tax Exempt InterestIncomeSecuritiesTaxExempt	5869000
CY2018	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	73000
CY2017	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	1266000
CY2019	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	714000
CY2018	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	200000
CY2017	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	6000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	64382000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	167809000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	183661000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	65028000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	168755000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	184134000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount	54606000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount	124235000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount	34838000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount	145321000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue	54937000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	127172000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	35494000
CY2019Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue	145656000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	129206000
CY2019Q4	fisi	Mortgage Servicing Assets Before Valuation Allowance MortgageServicingAssetsBeforeValuationAllowance	1128000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	1367000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	16613000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	264000
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	145819000
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	1631000
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	49517000
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	228000
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	30589000
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	395000
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue	80106000
CY2019Q4	fisi	Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	178723000
CY2019Q4	fisi	Investment Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	1595000
CY2019Q4	fisi	Investment Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	47202000
CY2019Q4	fisi	Investment Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	659000
CY2019Q4	fisi	Investment Securities Continuous Unrealized Loss Position Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue	225925000
CY2019Q4	fisi	Investment Securities Accumulated Unrecognized Holding Loss InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss	2254000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	251000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	1000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	438290000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	10749000
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	438541000
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	10750000
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	50519000
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	181000
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	234507000
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	7718000
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue	285026000
CY2018Q4	fisi	Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	50770000
CY2018Q4	fisi	Investment Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	182000
CY2018Q4	fisi	Investment Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	672797000
CY2018Q4	fisi	Investment Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	18467000
CY2018Q4	fisi	Investment Securities Continuous Unrealized Loss Position Fair Value InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue	723567000
CY2018Q4	fisi	Investment Securities Accumulated Unrecognized Holding Loss InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss	18649000
CY2019Q4	fisi	Investment Securities In Unrealized Loss Position Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions	91
CY2018Q4	fisi	Investment Securities In Unrealized Loss Position Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions	571
CY2019Q4	fisi	Investment Securities In Unrealized Loss Positions Twelve Months Or Longer Qualitative Disclosure Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions	34
CY2018Q4	fisi	Investment Securities In Unrealized Loss Positions Twelve Months Or Longer Qualitative Disclosure Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions	435
CY2018Q4	fisi	Investment Securities In Unrealized Loss Positions Less Than Twelve Months Qualitative Disclosure Number Of Positions InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions	136
CY2019	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale	0
CY2018	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale	0
CY2017	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale	0
CY2019Q4	fisi	Residential Real Estate Mortgages Serviced For Others ResidentialRealEstateMortgagesServicedForOthers	189800000
CY2018Q4	fisi	Residential Real Estate Mortgages Serviced For Others ResidentialRealEstateMortgagesServicedForOthers	171500000
CY2019Q4	us-gaap	Escrow Deposit EscrowDeposit	3900000
CY2018Q4	us-gaap	Escrow Deposit EscrowDeposit	3700000
CY2018Q4	fisi	Mortgage Servicing Assets Before Valuation Allowance MortgageServicingAssetsBeforeValuationAllowance	1021000
CY2017Q4	fisi	Mortgage Servicing Assets Before Valuation Allowance MortgageServicingAssetsBeforeValuationAllowance	990000
CY2016Q4	fisi	Mortgage Servicing Assets Before Valuation Allowance MortgageServicingAssetsBeforeValuationAllowance	1077000
CY2019	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	349000
CY2018	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	298000
CY2017	us-gaap	Servicing Asset At Fair Value Additions ServicingAssetAtFairValueAdditions	231000
CY2019	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	242000
CY2018	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	267000
CY2017	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	318000
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	60788000
CY2018Q4	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	2400000
CY2019Q4	fisi	Mortgage Servicing Assets Net Of Valuation Allowance MortgageServicingAssetsNetOfValuationAllowance	1128000
CY2018Q4	fisi	Mortgage Servicing Assets Net Of Valuation Allowance MortgageServicingAssetsNetOfValuationAllowance	1021000
CY2017Q4	fisi	Mortgage Servicing Assets Net Of Valuation Allowance MortgageServicingAssetsNetOfValuationAllowance	990000
CY2019Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	3179465000
CY2019Q4	fisi	Loans And Leases Receivable Deferred Loan Fees Costs LoansAndLeasesReceivableDeferredLoanFeesCosts	-41522000
CY2018Q4	fisi	Loans And Leases Receivable Deferred Loan Fees Costs LoansAndLeasesReceivableDeferredLoanFeesCosts	-42278000
CY2019Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3220987000
CY2018Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3086598000
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	18600000
CY2018Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	10300000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	9800000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Proceeds LoansAndLeasesReceivableRelatedPartiesProceeds	1600000
CY2019Q4	us-gaap	Financing Receivable Recorded Investment Past Due FinancingReceivableRecordedInvestmentPastDue	7081000
CY2018Q4	us-gaap	Financing Receivable Recorded Investment Past Due FinancingReceivableRecordedInvestmentPastDue	5713000
CY2019Q4	us-gaap	Financing Receivable Recorded Investment Nonaccrual Status FinancingReceivableRecordedInvestmentNonaccrualStatus	8634000
CY2018Q4	us-gaap	Financing Receivable Recorded Investment Nonaccrual Status FinancingReceivableRecordedInvestmentNonaccrualStatus	7133000
CY2019Q4	us-gaap	Financing Receivable Recorded Investment Current FinancingReceivableRecordedInvestmentCurrent	3163750000
CY2018Q4	us-gaap	Financing Receivable Recorded Investment Current FinancingReceivableRecordedInvestmentCurrent	3031474000
CY2019Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3179465000
CY2018Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3044320000
CY2019Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	0
CY2019	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	0
CY2018	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	0
CY2017	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	0
CY2019	us-gaap	Interest Income Operating InterestIncomeOperating	508000
CY2018	us-gaap	Interest Income Operating InterestIncomeOperating	294000
CY2017	us-gaap	Interest Income Operating InterestIncomeOperating	481000
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	0
CY2018	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	0
CY2019	us-gaap	Financing Receivable Modifications Subsequent Default Number Of Contracts1 FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1	0
CY2018	us-gaap	Financing Receivable Modifications Subsequent Default Number Of Contracts1 FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1	0
CY2019	fisi	Days Past Due When Loans Are Generally Placed On Nonaccrual Status In Days DaysPastDueWhenLoansAreGenerallyPlacedOnNonaccrualStatusInDays	P90D
CY2018	fisi	Days Past Due When Loans Are Generally Placed On Nonaccrual Status In Days DaysPastDueWhenLoansAreGenerallyPlacedOnNonaccrualStatusInDays	P90D
CY2019Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Recorded Investment ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment	1536000
CY2019Q4	us-gaap	Impaired Financing Receivable With Related Allowance Recorded Investment ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment	2787000
CY2019Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	4323000
CY2018Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Recorded Investment ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment	2332000
CY2018Q4	us-gaap	Impaired Financing Receivable With Related Allowance Recorded Investment ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment	746000
CY2018Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	3078000
CY2019Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	2524000
CY2019Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	2787000
CY2019Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	5311000
CY2018Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	3276000
CY2018Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	746000
CY2018Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	4022000
CY2019Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	693000
CY2018Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	206000
CY2019	us-gaap	Impaired Financing Receivable With No Related Allowance Average Recorded Investment ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment	2112000
CY2019	us-gaap	Impaired Financing Receivable With Related Allowance Average Recorded Investment ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment	3032000
CY2019	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	5144000
CY2018	us-gaap	Impaired Financing Receivable With No Related Allowance Average Recorded Investment ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment	1848000
CY2018	us-gaap	Impaired Financing Receivable With Related Allowance Average Recorded Investment ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment	4394000
CY2018	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	6242000
CY2019	us-gaap	Impaired Financing Receivable With No Related Allowance Interest Income Accrual Method ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
CY2019	us-gaap	Impaired Financing Receivable With Related Allowance Interest Income Accrual Method ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
CY2019	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod
CY2017	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	15235000
CY2019	us-gaap	Weighted Average Number Of Shares Restricted Stock WeightedAverageNumberOfSharesRestrictedStock	4000
CY2018	us-gaap	Weighted Average Number Of Shares Restricted Stock WeightedAverageNumberOfSharesRestrictedStock	8000
CY2017	us-gaap	Weighted Average Number Of Shares Restricted Stock WeightedAverageNumberOfSharesRestrictedStock	47000
CY2019	us-gaap	Weighted Average Number Of Shares Treasury Stock WeightedAverageNumberOfSharesTreasuryStock	110000
CY2018	us-gaap	Impaired Financing Receivable With No Related Allowance Interest Income Accrual Method ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
CY2018	us-gaap	Impaired Financing Receivable With Related Allowance Interest Income Accrual Method ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
CY2018	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	33914000
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	17811000
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	6335000
CY2019	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	8044000
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	30482000
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	693000
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	29789000
CY2019Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	4323000
CY2019Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	3175142000
CY2017Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	34672000
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	15734000
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	6042000
CY2018	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	8934000
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	206000
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	33708000
CY2018Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	3078000
CY2018Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	3041242000
CY2016Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	30934000
CY2017	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	15251000
CY2017	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	5628000
CY2017	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	13361000
CY2017Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	2108000
CY2017Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	32564000
CY2017Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	2694922000
CY2017Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	8174000
CY2017Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	2686748000
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	102212000
CY2018Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	99385000
CY2018Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	56546000
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0
CY2017Q2	fisi	Gain Loss On Contingent Consideration Liability Adjustment GainLossOnContingentConsiderationLiabilityAdjustment	1200000
CY2017Q2	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	1600000
CY2017Q4	us-gaap	Goodwill Goodwill	65840000
CY2018	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	2572000
CY2018Q4	us-gaap	Goodwill Goodwill	66062000
CY2019Q4	us-gaap	Goodwill Goodwill	66062000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	1134000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	1014000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	923000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	852000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	783000
CY2019	us-gaap	Lessee Operating Lease Description LesseeOperatingLeaseDescription	The Company is obligated under a number of non-cancellable operating lease agreements for land, buildings and equipment with terms, including renewal options reasonably certain to be exercised, extending through 2047
CY2019	us-gaap	Lessee Operating Sublease Option To Extend LesseeOperatingSubleaseOptionToExtend	One building lease is subleased for terms extending through 2021
CY2019	fisi	Number Of Buildings Subleased NumberOfBuildingsSubleased	1
CY2019Q4	fisi	Operating Lease Right Of Use Asset Gross OperatingLeaseRightOfUseAssetGross	23224000
CY2019Q4	fisi	Operating Lease Right Of Use Asset Accumulated Amortization OperatingLeaseRightOfUseAssetAccumulatedAmortization	1861000
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	21363000
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset Statement Of Financial Position Extensible List OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	us-gaap:OtherAssets
CY2018Q4	us-gaap	Operating Lease Right Of Use Asset Statement Of Financial Position Extensible List OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	us-gaap:OtherAssets
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	2758000
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	428000
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0380
CY2019	us-gaap	Sublease Income SubleaseIncome	46000
CY2019	us-gaap	Lease Cost LeaseCost	3140000
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	2641000
CY2019	fisi	Initial Recognition Of Operating Lease Right Of Use Assets InitialRecognitionOfOperatingLeaseRightOfUseAssets	23275000
CY2019	fisi	Initial Recognition Of Operating Lease Liabilities InitialRecognitionOfOperatingLeaseLiabilities	23985000
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	620000
CY2018	us-gaap	Operating Lease Expense OperatingLeaseExpense	2900
CY2017	us-gaap	Operating Lease Expense OperatingLeaseExpense	2600
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Rolling Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths	2523000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due In Rolling Year Two LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo	2308000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due In Rolling Year Three LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree	1857000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due In Rolling Year Four LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour	1493000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due In Rolling Year Five LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive	1182000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Rolling Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive	25931000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	35294000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	12494000
CY2019Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	1099488000
CY2018Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	871007000
CY2019Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	60868000
CY2018Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	91028000
CY2019Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	14869000
CY2018Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	40151000
CY2019Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	3251000
CY2018Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	15956000
CY2019Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	1708000
CY2018Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	1921000
CY2019Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	5000
CY2018Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	5000
CY2019Q4	us-gaap	Time Deposits100000 Or More TimeDeposits100000OrMore	287000000
CY2018Q4	us-gaap	Time Deposits100000 Or More TimeDeposits100000OrMore	209600000
CY2019	us-gaap	Interest Expense Demand Deposit Accounts InterestExpenseDemandDepositAccounts	1372000
CY2018	us-gaap	Interest Expense Demand Deposit Accounts InterestExpenseDemandDepositAccounts	1067000
CY2017	us-gaap	Interest Expense Demand Deposit Accounts InterestExpenseDemandDepositAccounts	897000
CY2019	us-gaap	Interest Expense Savings Deposits InterestExpenseSavingsDeposits	4365000
CY2018	us-gaap	Interest Expense Savings Deposits InterestExpenseSavingsDeposits	2887000
CY2017	us-gaap	Interest Expense Savings Deposits InterestExpenseSavingsDeposits	1487000
CY2019	us-gaap	Interest Expense Time Deposits InterestExpenseTimeDeposits	22757000
CY2018	us-gaap	Interest Expense Time Deposits InterestExpenseTimeDeposits	15101000
CY2017	us-gaap	Interest Expense Time Deposits InterestExpenseTimeDeposits	8709000
CY2019Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	275500000
CY2018Q4	us-gaap	Federal Home Loan Bank Advances Maturities Summary Due Within One Year Of Balance Sheet Date FederalHomeLoanBankAdvancesMaturitiesSummaryDueWithinOneYearOfBalanceSheetDate	405500000
CY2018Q4	us-gaap	Other Short Term Borrowings OtherShortTermBorrowings	64000000
CY2019Q4	us-gaap	Subordinated Debt SubordinatedDebt	39273000
CY2018Q4	us-gaap	Subordinated Debt SubordinatedDebt	39202000
CY2019Q4	us-gaap	Debt Longterm And Shortterm Combined Amount DebtLongtermAndShorttermCombinedAmount	314773000
CY2018Q4	us-gaap	Debt Longterm And Shortterm Combined Amount DebtLongtermAndShorttermCombinedAmount	508702000
CY2019Q4	us-gaap	Short Term Debt Weighted Average Interest Rate ShortTermDebtWeightedAverageInterestRate	0.0188
CY2018Q4	us-gaap	Short Term Debt Weighted Average Interest Rate ShortTermDebtWeightedAverageInterestRate	0.0264
CY2019Q4	us-gaap	Line Of Credit LineOfCredit	0
CY2018Q4	us-gaap	Line Of Credit LineOfCredit	0
CY2019Q4	us-gaap	Interest Rate Cash Flow Hedge Gain Loss To Be Reclassified During Next12 Months Net InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet	582000
CY2019Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	210000
CY2018	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-725000
CY2017	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-1142000
CY2019Q4	us-gaap	Capital Units Authorized CapitalUnitsAuthorized	50210000
CY2019Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	100
CY2019Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	173282
CY2018Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	173282
CY2019Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	173282
CY2018Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	173282
CY2019	us-gaap	Stock Issued During Period Shares Acquisitions StockIssuedDuringPeriodSharesAcquisitions	43378
CY2019	us-gaap	Stock Issued During Period Shares Restricted Stock Award Gross StockIssuedDuringPeriodSharesRestrictedStockAwardGross
CY2019	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised
CY2019	us-gaap	Stock Issued During Period Shares Treasury Stock Reissued StockIssuedDuringPeriodSharesTreasuryStockReissued
CY2019	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired
CY2017Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	16056178
CY2018	us-gaap	Stock Issued During Period Shares Restricted Stock Award Gross StockIssuedDuringPeriodSharesRestrictedStockAwardGross
CY2018	us-gaap	Stock Issued During Period Shares Restricted Stock Award Forfeited StockIssuedDuringPeriodSharesRestrictedStockAwardForfeited
CY2018	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised
CY2018	us-gaap	Stock Issued During Period Shares Treasury Stock Reissued StockIssuedDuringPeriodSharesTreasuryStockReissued
CY2018	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired
CY2019	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	12664000
CY2018	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	-12522000
CY2017	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	3313000
CY2019	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	3113000
CY2018	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-3157000
CY2017	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	1278000
CY2019	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	9374000
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-177000
CY2018	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	-10275000
CY2018	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-910000
CY2017	us-gaap	Other Comprehensive Income Loss Before Reclassifications Net Of Tax OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax	2028000
CY2017	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-7000
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Expiration Period SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod	P10Y
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0
CY2019Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	0
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	236000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	297000
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8882000
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	19351000
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	-3031000
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	1308000
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	1135000
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	573000
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	10190000
CY2018	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	20486000
CY2017	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	-2458000
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	280000
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-10303000
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	12297000
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	89000
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-177000
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	106000
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	-0.019
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	-0.026
CY2019Q4	us-gaap	Investments And Cash InvestmentsAndCash	87827000
CY2019Q4	us-gaap	Pension And Other Postretirement And Postemployment Benefit Plans Liabilities Current And Noncurrent PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent	110000
CY2019Q4	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Before Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax	19990000
CY2018Q4	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Before Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax	20509000
CY2019	us-gaap	Other Comprehensive Income Defined Benefit Plans Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent	5122000
CY2018	us-gaap	Other Comprehensive Income Defined Benefit Plans Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansTaxPortionAttributableToParent	7273000
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	14868000
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	13236000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	6145000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	34000
CY2019Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Value FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue	0
CY2018Q4	us-gaap	Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Value FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue	0
CY2018	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	1169000
CY2017	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	1973000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	-0.056
CY2019	fisi	Effective Income Tax Rate Reconciliation Tax Credit And Adjustments Percent EffectiveIncomeTaxRateReconciliationTaxCreditAndAdjustmentsPercent	-0.030
CY2018	fisi	Effective Income Tax Rate Reconciliation Tax Credit And Adjustments Percent EffectiveIncomeTaxRateReconciliationTaxCreditAndAdjustmentsPercent	-0.003
CY2017	fisi	Effective Income Tax Rate Reconciliation Tax Credit And Adjustments Percent EffectiveIncomeTaxRateReconciliationTaxCreditAndAdjustmentsPercent	-0.067
CY2019	fisi	Effective Income Tax Rate Reconciliation Non Taxable Earnings On Company Owned Life Insurance EffectiveIncomeTaxRateReconciliationNonTaxableEarningsOnCompanyOwnedLifeInsurance	-0.006
CY2018	fisi	Effective Income Tax Rate Reconciliation Non Taxable Earnings On Company Owned Life Insurance EffectiveIncomeTaxRateReconciliationNonTaxableEarningsOnCompanyOwnedLifeInsurance	-0.008
CY2017	fisi	Effective Income Tax Rate Reconciliation Non Taxable Earnings On Company Owned Life Insurance EffectiveIncomeTaxRateReconciliationNonTaxableEarningsOnCompanyOwnedLifeInsurance	-0.014
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.019
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.015
CY2017	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.011
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	0.002
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	0.002
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	0.003
CY2018	fisi	Effective Income Tax Rate Reconciliation Goodwill And Contingent Consideration Adjustments Percent EffectiveIncomeTaxRateReconciliationGoodwillAndContingentConsiderationAdjustmentsPercent	0.010
CY2017	fisi	Effective Income Tax Rate Reconciliation Goodwill And Contingent Consideration Adjustments Percent EffectiveIncomeTaxRateReconciliationGoodwillAndContingentConsiderationAdjustmentsPercent	0.003
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.002
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.002
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.178
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.202
CY2017	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.229
CY2019	us-gaap	Income Tax Effects Allocated Directly To Equity IncomeTaxEffectsAllocatedDirectlyToEquity	3113000
CY2018	us-gaap	Income Tax Effects Allocated Directly To Equity IncomeTaxEffectsAllocatedDirectlyToEquity	-3156000
CY2017	us-gaap	Income Tax Effects Allocated Directly To Equity IncomeTaxEffectsAllocatedDirectlyToEquity	3909000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Allowance For Doubtful Accounts DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAllowanceForDoubtfulAccounts	7810000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Allowance For Doubtful Accounts DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAllowanceForDoubtfulAccounts	8550000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	1095000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	1771000
CY2019Q4	us-gaap	Deferred Tax Assets Equity Method Investments DeferredTaxAssetsEquityMethodInvestments	1191000
CY2018Q4	us-gaap	Deferred Tax Assets Equity Method Investments DeferredTaxAssetsEquityMethodInvestments	660000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	418000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	417000
CY2019Q4	fisi	Deferred Tax Assets Interest On Nonaccrual Loans DeferredTaxAssetsInterestOnNonaccrualLoans	191000
CY2018Q4	fisi	Deferred Tax Assets Interest On Nonaccrual Loans DeferredTaxAssetsInterestOnNonaccrualLoans	106000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	586000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	541000
CY2018Q4	fisi	Deferred Tax Asets Net Unrealized Loss On Securities Available For Sale DeferredTaxAsetsNetUnrealizedLossOnSecuritiesAvailableForSale	2848000
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	224000
CY2018Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	138000
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	11515000
CY2018Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	15031000
CY2019Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	498000
CY2018Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	583000
CY2019Q4	fisi	Deferred Tax Liabilities Prepaid Pension Costs DeferredTaxLiabilitiesPrepaidPensionCosts	897000
CY2018Q4	fisi	Deferred Tax Liabilities Prepaid Pension Costs DeferredTaxLiabilitiesPrepaidPensionCosts	1415000
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	2643000
CY2018Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	2581000
CY2019Q4	fisi	Deferred Tax Liabilities Depreciation And Amortization DeferredTaxLiabilitiesDepreciationAndAmortization	1961000
CY2018Q4	fisi	Deferred Tax Liabilities Depreciation And Amortization DeferredTaxLiabilitiesDepreciationAndAmortization	2096000
CY2019Q4	fisi	Deferred Tax Liabilities Net Unrealized Gain On Securities Available For Sale DeferredTaxLiabilitiesNetUnrealizedGainOnSecuritiesAvailableForSale	301000
CY2019Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	289000
CY2018Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	258000
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	550000
CY2018Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	240000
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	7139000
CY2018Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	7173000
CY2019Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	4376000
CY2018	us-gaap	Weighted Average Number Of Shares Treasury Stock WeightedAverageNumberOfSharesTreasuryStock	138000
CY2018Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	7858000
CY2019	fisi	Tax Cuts And Jobs Act Of2017 Maximum Operating Loss Carryforwards Percentage TaxCutsAndJobsActOf2017MaximumOperatingLossCarryforwardsPercentage	0.80
CY2017Q4	fisi	Tax Cuts And Jobs Act Of2017 Change In Tax Rate Deferred Tax Liability Income Tax Expense Benefit TaxCutsAndJobsActOf2017ChangeInTaxRateDeferredTaxLiabilityIncomeTaxExpenseBenefit	2900000
CY2017	fisi	Tax Cuts And Jobs Act Of2017 Change In Tax Rate Deferred Tax Liability Income Tax Expense Benefit TaxCutsAndJobsActOf2017ChangeInTaxRateDeferredTaxLiabilityIncomeTaxExpenseBenefit	2900000
CY2019	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0
CY2018	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0
CY2017	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Expense UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense	0
CY2019Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	0
CY2018Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	0
CY2019	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	16086000
CY2018	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	16056000
CY2017	us-gaap	Weighted Average Number Of Shares Treasury Stock WeightedAverageNumberOfSharesTreasuryStock	144000
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	2000
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	9000
CY2019	fisi	Incremental Common Shares Attributable To Vesting Of Restricted Stock Awards IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards	59000
CY2018	fisi	Incremental Common Shares Attributable To Vesting Of Restricted Stock Awards IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards	44000
CY2017	fisi	Incremental Common Shares Attributable To Vesting Of Restricted Stock Awards IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards	32000
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	4000
CY2018	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	6000
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1000
CY2019	us-gaap	Incremental Common Shares Attributable To Participating Nonvested Shares With Non Forfeitable Dividend Rights IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights	0
CY2018	us-gaap	Incremental Common Shares Attributable To Participating Nonvested Shares With Non Forfeitable Dividend Rights IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights	0
CY2017	us-gaap	Incremental Common Shares Attributable To Participating Nonvested Shares With Non Forfeitable Dividend Rights IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights	0
CY2019Q4	us-gaap	Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets Aggregate Projected Benefit Obligation DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation	0
CY2018Q4	us-gaap	Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets Aggregate Projected Benefit Obligation DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation	0
CY2017Q4	us-gaap	Defined Benefit Plan Pension Plans With Accumulated Benefit Obligations In Excess Of Plan Assets Aggregate Projected Benefit Obligation DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation	0
CY2018Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	69574000
CY2017Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	70436000
CY2019	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	3207000
CY2018	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	3346000
CY2019	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	2777000
CY2018	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	2387000
CY2019	us-gaap	Defined Benefit Plan Actuarial Gain Loss DefinedBenefitPlanActuarialGainLoss	-11993000
CY2018	us-gaap	Defined Benefit Plan Actuarial Gain Loss DefinedBenefitPlanActuarialGainLoss	3298000
CY2019	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	3223000
CY2018	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	3297000
CY2019Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	84328000
CY2018Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	75188000
CY2017Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	83348000
CY2019	us-gaap	Defined Benefit Plan Actual Return On Plan Assets DefinedBenefitPlanActualReturnOnPlanAssets	15862000
CY2018	us-gaap	Defined Benefit Plan Actual Return On Plan Assets DefinedBenefitPlanActualReturnOnPlanAssets	-4863000
CY2019	us-gaap	Defined Benefit Plan Plan Assets Benefits Paid DefinedBenefitPlanPlanAssetsBenefitsPaid	3223000
CY2018	us-gaap	Defined Benefit Plan Plan Assets Benefits Paid DefinedBenefitPlanPlanAssetsBenefitsPaid	3297000
CY2019Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	87827000
CY2019Q4	us-gaap	Defined Benefit Plan Funded Status Of Plan DefinedBenefitPlanFundedStatusOfPlan	3499000
CY2018Q4	us-gaap	Defined Benefit Plan Funded Status Of Plan DefinedBenefitPlanFundedStatusOfPlan	5614000
CY2019Q4	us-gaap	Defined Benefit Plan Accumulated Benefit Obligation DefinedBenefitPlanAccumulatedBenefitObligation	76800000
CY2018Q4	us-gaap	Defined Benefit Plan Accumulated Benefit Obligation DefinedBenefitPlanAccumulatedBenefitObligation	63300000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Next Twelve Months DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths	3872000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Two DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo	3475000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Three DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree	3855000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Four DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour	4127000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Five DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive	4215000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter	23491000
CY2017	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	3140000
CY2017	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	2449000
CY2019	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	4736000
CY2018	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	5284000
CY2017	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	4775000
CY2019	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-1445000
CY2018	us-gaap	Defined Benefit Plan Amortization Of Prior Service Cost Credit DefinedBenefitPlanAmortizationOfPriorServiceCostCredit	-5000
CY2017	us-gaap	Defined Benefit Plan Amortization Of Prior Service Cost Credit DefinedBenefitPlanAmortizationOfPriorServiceCostCredit	17000
CY2019	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	2693000
CY2019	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0413
CY2018	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0349
CY2017	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0400
CY2019	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease	0.0300
CY2018	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease	0.0300
CY2017	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease	0.0300
CY2019	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0650
CY2018	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0650
CY2017	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0650
CY2019Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate	0.0309
CY2018Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate	0.0413
CY2017Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate	0.0349
CY2019Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease	0.0300
CY2018Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease	0.0300
CY2017Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Rate Of Compensation Increase DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease	0.0300
CY2019	fisi	Investment Strategy Percentage In Long Term Growth InvestmentStrategyPercentageInLongTermGrowth	0.97
CY2019	fisi	Investment Strategy Percentage In Near Term Benefit Payments InvestmentStrategyPercentageInNearTermBenefitPayments	0.03
CY2019	fisi	Maximum Percentage Of Securities Purchasing Allowed Of Portfolio At Any Time MaximumPercentageOfSecuritiesPurchasingAllowedOfPortfolioAtAnyTime	0.05
CY2019	fisi	Maximum Market Value Purchase Percentage Allowed Of Any One Issuer MaximumMarketValuePurchasePercentageAllowedOfAnyOneIssuer	0.08
CY2019Q4	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	1845000
CY2019Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	30685000
CY2019Q4	fisi	Fixed Income Securities FixedIncomeSecurities	49571000
CY2019Q4	us-gaap	Defined Benefit Plan Weighted Average Asset Allocations DefinedBenefitPlanWeightedAverageAssetAllocations	0.98
CY2018Q4	us-gaap	Cash Equivalents At Carrying Value CashEquivalentsAtCarryingValue	3122000
CY2018Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	34697000
CY2018Q4	fisi	Fixed Income Securities FixedIncomeSecurities	34472000
CY2018Q4	us-gaap	Investments And Cash InvestmentsAndCash	75188000
CY2018Q4	us-gaap	Pension And Other Postretirement And Postemployment Benefit Plans Liabilities Current And Noncurrent PensionAndOtherPostretirementAndPostemploymentBenefitPlansLiabilitiesCurrentAndNoncurrent	109000
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-519000
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	1300000
CY2019Q4	us-gaap	Fair Value Assets Level1 To Level2 Transfers Amount FairValueAssetsLevel1ToLevel2TransfersAmount	0
CY2018Q4	us-gaap	Fair Value Assets Level1 To Level2 Transfers Amount FairValueAssetsLevel1ToLevel2TransfersAmount	0
CY2019Q4	us-gaap	Fair Value Assets Level2 To Level1 Transfers Amount FairValueAssetsLevel2ToLevel1TransfersAmount	0
CY2018Q4	us-gaap	Fair Value Assets Level2 To Level1 Transfers Amount FairValueAssetsLevel2ToLevel1TransfersAmount	0
CY2019Q4	us-gaap	Fair Value Liabilities Level2 To Level1 Transfers Amount FairValueLiabilitiesLevel2ToLevel1TransfersAmount	0
CY2018Q4	us-gaap	Fair Value Liabilities Level2 To Level1 Transfers Amount FairValueLiabilitiesLevel2ToLevel1TransfersAmount	0
CY2017Q4	us-gaap	Fair Value Assets Level1 To Level2 Transfers Amount FairValueAssetsLevel1ToLevel2TransfersAmount	0
CY2017Q4	us-gaap	Fair Value Assets Level2 To Level1 Transfers Amount FairValueAssetsLevel2ToLevel1TransfersAmount	0
CY2017Q4	us-gaap	Fair Value Liabilities Level2 To Level1 Transfers Amount FairValueLiabilitiesLevel2ToLevel1TransfersAmount	0
CY2019	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	2
CY2019Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	8861000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	10111000

Files In Submission

Name	View Source	Status
0001564590-20-008690-index-headers.html	Edgar Link	pending
0001564590-20-008690-index.html	Edgar Link	pending
0001564590-20-008690.txt	Edgar Link	pending
0001564590-20-008690-xbrl.zip	Edgar Link	pending
FilingSummary.xml	Edgar Link	unprocessable
Financial_Report.xlsx	Edgar Link	pending
fisi-10k_20191231.htm	Edgar Link	pending
fisi-20191231.xml	Edgar Link	completed
fisi-20191231.xsd	Edgar Link	pending
fisi-20191231_cal.xml	Edgar Link	unprocessable
fisi-20191231_def.xml	Edgar Link	unprocessable
fisi-20191231_lab.xml	Edgar Link	unprocessable
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fisi-ex21_7.htm	Edgar Link	pending
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$FISI
FINANCIAL INSTITUTIONS INC Stock $fisi

2018 Q4 Form 10-K Financial Statement

#000156459020008690 Filed on March 04, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$FISI FINANCIAL INSTITUTIONS INC Stock $fisi

2018 Q4 Form 10-K Financial Statement

#000156459020008690 Filed on March 04, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$FISI
FINANCIAL INSTITUTIONS INC Stock $fisi