$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

$cbu Overview Financials Valuation SEC Filings Company Website

2019 Q4 Form 10-K Financial Statement

#000110465921030055 Filed on March 01, 2021

Income Statement

Concept	2019 Q4	2019 Q3	2018 Q4
Revenue		$98.65M
YoY Change		8.52%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development		$10.68M
YoY Change		1.58%
% of Gross Profit
Depreciation & Amortization	$8.100M	$8.200M	$8.300M
YoY Change	-2.41%	-2.38%	-7.78%
% of Gross Profit
Operating Expenses		$10.68M
YoY Change		1.58%
Operating Profit
YoY Change
Interest Expense		$7.371M
YoY Change		56.66%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$51.70M	$49.69M	$51.50M
YoY Change	0.39%	-8.89%	8.19%
Income Tax	$8.900M	$10.47M	$10.70M
% Of Pretax Income	17.21%	21.07%	20.78%
Net Earnings	$42.90M	$39.22M	$40.80M
YoY Change	5.15%	-9.02%	-43.33%
Net Earnings / Revenue		39.76%
Basic Earnings Per Share		$0.76
Diluted Earnings Per Share	$817.1K	$0.75	$786.1K
COMMON SHARES
Basic Shares Outstanding	51.70M	51.75M
Diluted Shares Outstanding		52.25M

Balance Sheet

Concept	2019 Q4	2019 Q3	2018 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$205.0M	$1.014B	$211.8M
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	$164.6M	$169.9M	$120.0M
YoY Change	37.21%	41.61%	-2.45%
Goodwill	$773.8M	$39.97M	$733.5M
YoY Change	5.5%	-94.55%	-0.13%
Intangibles	$63.11M	$67.08M	$73.85M
YoY Change	-14.53%	-14.25%	-18.54%
Long-Term Investments
YoY Change
Other Assets
YoY Change
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$11.41B	$11.60B	$10.61B
YoY Change	7.57%	8.8%	-1.29%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$174.0M	$216.0M	$157.0M
YoY Change	10.83%	41.18%	-13.26%
Accrued Expenses	$41.00M	$43.00M
YoY Change
Deferred Revenue
YoY Change
Short-Term Debt	$242.0M	$233.0M	$259.0M
YoY Change	-6.56%	-15.27%	-23.15%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$215.0M	$259.0M	$157.0M
YoY Change	36.94%	69.28%	-13.26%
LONG-TERM LIABILITIES
Long-Term Debt	$91.00M	$91.00M	$98.00M
YoY Change	-7.14%	-7.14%	-20.33%
Other Long-Term Liabilities	$1.000M	$1.000M
YoY Change
Total Long-Term Liabilities	$92.00M	$92.00M	$98.00M
YoY Change	-6.12%	-6.12%	-20.33%
TOTAL LIABILITIES
Total Short-Term Liabilities	$215.0M	$259.0M	$157.0M
Total Long-Term Liabilities	$92.00M	$92.00M	$98.00M
Total Liabilities	$9.555B	$9.757B	$8.894B
YoY Change	7.44%	8.52%	-2.39%
SHAREHOLDERS EQUITY
Retained Earnings	$882.9M	$861.3M	$795.6M
YoY Change	10.97%
Common Stock
YoY Change
Preferred Stock
YoY Change
Treasury Stock (at cost)	$6.823M	$6.875M	$11.53M
YoY Change	-40.81%
Treasury Stock Shares	$180.8K	$182.9K	$319.0K
Shareholders Equity	$1.855B	$1.840B	$1.714B
YoY Change
Total Liabilities & Shareholders Equity	$11.41B	$11.60B	$10.61B
YoY Change	7.57%	8.79%	-1.29%

Cashflow Statement

Concept	2019 Q4	2019 Q3	2018 Q4
OPERATING ACTIVITIES
Net Income	$42.90M	$39.22M	$40.80M
YoY Change	5.15%	-9.02%	-43.33%
Depreciation, Depletion And Amortization	$8.100M	$8.200M	$8.300M
YoY Change	-2.41%	-2.38%	-7.78%
Cash From Operating Activities	$73.50M	$39.10M	$53.60M
YoY Change	37.13%	-28.91%	5.51%
INVESTING ACTIVITIES
Capital Expenditures	-$700.0K	-$1.000M	-$3.700M
YoY Change	-81.08%	-72.22%	19.35%
Acquisitions		$500.0K
YoY Change
Other Investing Activities	-$708.0M	-$64.00M	$20.90M
YoY Change	-3487.56%	36.46%	-64.52%
Cash From Investing Activities	-$708.7M	-$65.10M	$17.20M
YoY Change	-4220.35%	28.91%	-69.18%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-174.0M	165.3M	-115.8M
YoY Change	50.26%	7413.64%	-8.89%
NET CHANGE
Cash From Operating Activities	73.50M	39.10M	53.60M
Cash From Investing Activities	-708.7M	-65.10M	17.20M
Cash From Financing Activities	-174.0M	165.3M	-115.8M
Net Change In Cash	-809.2M	139.3M	-45.00M
YoY Change	1698.22%	1979.1%	119.51%
FREE CASH FLOW
Cash From Operating Activities	$73.50M	$39.10M	$53.60M
Capital Expenditures	-$700.0K	-$1.000M	-$3.700M
Free Cash Flow	$74.20M	$40.10M	$57.30M
YoY Change	29.49%	-31.57%	6.31%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value
CY2020	dei	Amendment Flag AmendmentFlag	false
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	4000000
CY2020	dei	Entity Central Index Key EntityCentralIndexKey	0000723188
CY2020	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2020	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
CY2020	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2020	dei	Entity Registrant Name EntityRegistrantName	COMMUNITY BANK SYSTEM, INC.
CY2020Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies
CY2019Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset Statement Of Financial Position Extensible List OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	us-gaap:PropertyPlantAndEquipmentNet
CY2019Q4	us-gaap	Operating Lease Liability Statement Of Financial Position Extensible List OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList	us-gaap:OperatingLeaseLiability
CY2020Q4	us-gaap	Operating Lease Liability Statement Of Financial Position Extensible List OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList	us-gaap:OperatingLeaseLiability
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P6Y1M6D
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P6Y7M6D
CY2020	dei	Document Type DocumentType	10-K
CY2020	dei	Document Annual Report DocumentAnnualReport	true
CY2020	dei	Document Period End Date DocumentPeriodEndDate	2020-12-31
CY2020	dei	Document Transition Report DocumentTransitionReport	false
CY2020	dei	Entity File Number EntityFileNumber	001-13695
CY2020	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2020	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	16-1213679
CY2020	dei	Entity Address Address Line1 EntityAddressAddressLine1	5790 Widewaters Parkway
CY2020	dei	Entity Address City Or Town EntityAddressCityOrTown	DeWitt
CY2020	dei	Entity Address State Or Province EntityAddressStateOrProvince	NY
CY2020	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	13214
CY2020	dei	City Area Code CityAreaCode	315
CY2020	dei	Local Phone Number LocalPhoneNumber	445-2282
CY2020	dei	Security12b Title Security12bTitle	Common Stock, $1.00 par value per share
CY2020	dei	Trading Symbol TradingSymbol	CBU
CY2020	dei	Security Exchange Name SecurityExchangeName	NYSE
CY2020	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2020	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2020	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2020	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2020	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2020	dei	Entity Small Business EntitySmallBusiness	false
CY2020	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2020	dei	Icfr Auditor Attestation Flag IcfrAuditorAttestationFlag	true
CY2020	dei	Entity Shell Company EntityShellCompany	false
CY2020Q2	dei	Entity Public Float EntityPublicFloat	3000356306
CY2021Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	53675085
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	1645805000
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CY2020Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	3427779000
CY2019Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	3011551000
CY2020Q4	us-gaap	Available For Sale Securities AvailableForSaleSecurities	3547892000
CY2019Q4	us-gaap	Available For Sale Securities AvailableForSaleSecurities	3044428000
CY2020Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	46511000
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CY2019Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	42965000
CY2020Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	47455000
CY2019Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	43915000
CY2020Q4	us-gaap	Loans Receivable Held For Sale Net Not Part Of Disposal Group LoansReceivableHeldForSaleNetNotPartOfDisposalGroup	1622000
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CY2019Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	6890543000
CY2020Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	60869000
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49911000
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CY2019Q4	cbu	Core Deposit Intangibles Net CoreDepositIntangiblesNet	16418000
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CY2020Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	0
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CY2020Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	284008000
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CY2018	us-gaap	Labor And Related Expense LaborAndRelatedExpense	207363000
CY2020	us-gaap	Occupancy Net OccupancyNet	40732000
CY2019	us-gaap	Occupancy Net OccupancyNet	39850000
CY2018	us-gaap	Occupancy Net OccupancyNet	39948000
CY2020	us-gaap	Communications And Information Technology CommunicationsAndInformationTechnology	45755000
CY2019	us-gaap	Communications And Information Technology CommunicationsAndInformationTechnology	41407000
CY2018	us-gaap	Communications And Information Technology CommunicationsAndInformationTechnology	39094000
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	14297000
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15956000
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	18155000
CY2020	us-gaap	Professional Fees ProfessionalFees	11605000
CY2019	us-gaap	Professional Fees ProfessionalFees	10783000
CY2018	us-gaap	Professional Fees ProfessionalFees	10644000
CY2020	us-gaap	Business Development BusinessDevelopment	9463000
CY2019	us-gaap	Business Development BusinessDevelopment	11416000
CY2018	us-gaap	Business Development BusinessDevelopment	9383000
CY2020	us-gaap	Litigation Settlement Expense LitigationSettlementExpense	2950000
CY2019	us-gaap	Litigation Settlement Expense LitigationSettlementExpense	0
CY2018	us-gaap	Litigation Settlement Expense LitigationSettlementExpense	0
CY2020	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	4933000
CY2019	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	8608000
CY2018	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	-769000
CY2020	us-gaap	Other Noninterest Expense OtherNoninterestExpense	18415000
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	24090000
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	21471000
CY2020	us-gaap	Noninterest Expense NoninterestExpense	376534000
CY2019	us-gaap	Noninterest Expense NoninterestExpense	372026000
CY2018	us-gaap	Noninterest Expense NoninterestExpense	345289000
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	206076000
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	209338000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	212988000
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	41400000
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	40275000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	44347000
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.10
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.26
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.28
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.08
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.23
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.24
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-8379000
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	2563000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	12647000
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-2012000
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	605000
CY2019	cbu	Stock Issued During Period Value Deferred Compensation Arrangements StockIssuedDuringPeriodValueDeferredCompensationArrangements	0
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	3087000
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-6367000
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	1958000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	9560000
CY2020	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-471000
CY2019	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-115000
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	4882000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	0
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	-1398000
CY2020	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-113000
CY2019	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-28000
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-340000
CY2020	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-358000
CY2019	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-87000
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax	-1058000
CY2020	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionBeforeTax	0
CY2019	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionBeforeTax	0
CY2018	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionBeforeTax	-775000
CY2020	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionTax	0
CY2019	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionTax	0
CY2018	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionTax	-189000
CY2020	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionNetOfTax	0
CY2019	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionNetOfTax	0
CY2018	cbu	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Initial Projected Benefit Obligation Recognized Upon Plan Adoption Net Of Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForInitialProjectedBenefitObligationRecognizedUponPlanAdoptionNetOfTax	-586000
CY2020	us-gaap	Other Comprehensive Income Defined Benefit Plans Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent	-6009000
CY2019	us-gaap	Other Comprehensive Income Defined Benefit Plans Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent	2045000
CY2018	us-gaap	Other Comprehensive Income Defined Benefit Plans Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent	11204000
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	87237000
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	53988000
CY2018	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	-39894000
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	20943000
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	13176000
CY2018	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	-9700000
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	66294000
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	40812000
CY2018	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	-30194000
CY2020	cbu	Other Comprehensive Income Reclassification Adjustment For Equity Securities Net Of Tax OtherComprehensiveIncomeReclassificationAdjustmentForEquitySecuritiesNetOfTax	0
CY2019	cbu	Other Comprehensive Income Reclassification Adjustment For Equity Securities Net Of Tax OtherComprehensiveIncomeReclassificationAdjustmentForEquitySecuritiesNetOfTax	0
CY2018	cbu	Other Comprehensive Income Reclassification Adjustment For Equity Securities Net Of Tax OtherComprehensiveIncomeReclassificationAdjustmentForEquitySecuritiesNetOfTax	-208000
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	0
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	0
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	1194000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	0
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	0
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	3688000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	0
CY2020	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	66294000
CY2019	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	37124000
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	5285000
CY2018	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-30402000
CY2020	cbu	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Including Cumulative Effect Of Change In Accounting Principle OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentIncludingCumulativeEffectOfChangeInAccountingPrinciple	72303000
CY2019	cbu	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Including Cumulative Effect Of Change In Accounting Principle OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentIncludingCumulativeEffectOfChangeInAccountingPrinciple	35079000
CY2018	cbu	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Including Cumulative Effect Of Change In Accounting Principle OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentIncludingCumulativeEffectOfChangeInAccountingPrinciple	-41606000
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2020	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	236979000
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	204142000
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	127035000
CY2020Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Gross Of Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansGrossOfTax	38267000
CY2019Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Gross Of Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansGrossOfTax	46175000
CY2018Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Gross Of Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansGrossOfTax	43497000
CY2020Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax Effect AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTaxEffect	-9394000
CY2019Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax Effect AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTaxEffect	-11293000
CY2018Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax Effect AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTaxEffect	-10660000
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	28873000
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	34882000
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	32837000
CY2020Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Gross AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentGross	120114000
CY2019Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Gross AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentGross	32877000
CY2018Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Gross AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentGross	-16229000
CY2020Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Tax Effect AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentTaxEffect	29164000
CY2019Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Tax Effect AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentTaxEffect	8221000
CY2018Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Tax Effect AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentTaxEffect	-3761000
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	90950000
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	24656000
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	-12468000
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	62077000
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-10226000
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-45305000
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	1635315000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-41398000
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.44
CY2018	us-gaap	Dividends Common Stock DividendsCommonStock	73843000
CY2018	cbu	Stock Issued During Period Value Employee Stock Ownership Plan Net Of Impact Of Net Settlement Of Tax Withholding Obligations StockIssuedDuringPeriodValueEmployeeStockOwnershipPlanNetOfImpactOfNetSettlementOfTaxWithholdingObligations	6443000
CY2018	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	6064000
CY2018	cbu	Stock Issued During Period Value Deferred Compensation Arrangements StockIssuedDuringPeriodValueDeferredCompensationArrangements	0
CY2018	cbu	Treasury Stock Value Acquired And Issued To Deferred Compensation Arrangements Cost Method TreasuryStockValueAcquiredAndIssuedToDeferredCompensationArrangementsCostMethod	0
CY2018	us-gaap	Stock Issued During Period Value Employee Benefit Plan StockIssuedDuringPeriodValueEmployeeBenefitPlan	12561000
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	1713783000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	35079000
CY2019	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.58
CY2019	us-gaap	Dividends Common Stock DividendsCommonStock	81775000
CY2019	cbu	Stock Issued During Period Value Employee Stock Ownership Plan Net Of Impact Of Net Settlement Of Tax Withholding Obligations StockIssuedDuringPeriodValueEmployeeStockOwnershipPlanNetOfImpactOfNetSettlementOfTaxWithholdingObligations	6915000
CY2019	cbu	Treasury Stock Value Acquired And Issued To Deferred Compensation Arrangements Cost Method TreasuryStockValueAcquiredAndIssuedToDeferredCompensationArrangementsCostMethod	0
CY2019	us-gaap	Stock Issued During Period Value Employee Benefit Plan StockIssuedDuringPeriodValueEmployeeBenefitPlan	6884000
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	1855234000
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	72303000
CY2020	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.66
CY2020	us-gaap	Dividends Common Stock DividendsCommonStock	88484000
CY2020	cbu	Stock Issued During Period Value Employee Stock Ownership Plan Net Of Impact Of Net Settlement Of Tax Withholding Obligations StockIssuedDuringPeriodValueEmployeeStockOwnershipPlanNetOfImpactOfNetSettlementOfTaxWithholdingObligations	15792000
CY2020	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	6419000
CY2020	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	76942000
CY2020	cbu	Stock Issued During Period Value Deferred Compensation Arrangements StockIssuedDuringPeriodValueDeferredCompensationArrangements	0
CY2020	cbu	Treasury Stock Value Acquired And Issued To Deferred Compensation Arrangements Cost Method TreasuryStockValueAcquiredAndIssuedToDeferredCompensationArrangementsCostMethod	0
CY2020	us-gaap	Stock Issued During Period Value Employee Benefit Plan StockIssuedDuringPeriodValueEmployeeBenefitPlan	85000
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	2104107000
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2020	us-gaap	Depreciation Depreciation	15963000
CY2019	us-gaap	Depreciation Depreciation	15891000
CY2018	us-gaap	Depreciation Depreciation	15749000
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	14297000
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15956000
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	18155000
CY2020	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	11353000
CY2019	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	6176000
CY2018	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	9404000
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	6419000
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	5285000
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	6064000
CY2020	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	14212000
CY2019	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	8430000
CY2018	us-gaap	Provision For Loan Lease And Other Losses ProvisionForLoanLeaseAndOtherLosses	10837000
CY2020	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	2336000
CY2019	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	2302000
CY2018	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	-2663000
CY2020	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	379000
CY2019	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	378000
CY2018	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	449000
CY2020	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-6000
CY2019	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	19000
CY2018	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	657000
CY2020	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	421000
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	0
CY2018	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-318000
CY2020	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1915000
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1678000
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1579000
CY2020	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	0
CY2018	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	80000
CY2020	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	16939000
CY2019	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-2545000
CY2018	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-10252000
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	179483000
CY2019	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	4882000
CY2018	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	0
CY2020	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	3505000
CY2019	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	-11000
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	202502000
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	221408000
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	0
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	590179000
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	0
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	885549000
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	209857000
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	140784000
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Other Investments ProceedsFromMaturitiesPrepaymentsAndCallsOfOtherInvestments	516000
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Other Investments ProceedsFromMaturitiesPrepaymentsAndCallsOfOtherInvestments	3995000
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Other Investments ProceedsFromMaturitiesPrepaymentsAndCallsOfOtherInvestments	5867000
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	1114914000
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	810122000
CY2018	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	78131000
CY2020	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	3234000
CY2019	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	202000
CY2018	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	31000
CY2020	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	185131000
CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	140382000
CY2018	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	35414000
CY2020	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	55973000
CY2019	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	90381000
CY2018	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	16000
CY2020	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	-34360000
CY2019	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	4653000
CY2018	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	1737000
CY2020	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	0
CY2019	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	1597000
CY2018	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	0
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	14395000
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	5686000
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	12646000
CY2020	us-gaap	Payments For Proceeds From Real Estate Partnership Investment Net PaymentsForProceedsFromRealEstatePartnershipInvestmentNet	1471000
CY2019	us-gaap	Payments For Proceeds From Real Estate Partnership Investment Net PaymentsForProceedsFromRealEstatePartnershipInvestmentNet	1637000
CY2018	us-gaap	Payments For Proceeds From Real Estate Partnership Investment Net PaymentsForProceedsFromRealEstatePartnershipInvestmentNet	1197000
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-398720000
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-157054000
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	17495000
CY2020	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	1713733000
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	104435000
CY2018	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	-122049000
CY2020	us-gaap	Repayments Of Debt RepaymentsOfDebt	3092000
CY2019	us-gaap	Repayments Of Debt RepaymentsOfDebt	646000
CY2018	us-gaap	Repayments Of Debt RepaymentsOfDebt	95000
CY2020	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	30908000
CY2019	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-64405000
CY2018	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-47339000
CY2020	cbu	Repayments Of Subordinated Debt Held By Unconsolidated Subsidiary Trusts RepaymentsOfSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts	2062000
CY2019	cbu	Repayments Of Subordinated Debt Held By Unconsolidated Subsidiary Trusts RepaymentsOfSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts	22681000
CY2018	cbu	Repayments Of Subordinated Debt Held By Unconsolidated Subsidiary Trusts RepaymentsOfSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts	25207000
CY2020	cbu	Repayment Of Subordinate Notes Payable RepaymentOfSubordinateNotesPayable	10000000
CY2019	cbu	Repayment Of Subordinate Notes Payable RepaymentOfSubordinateNotesPayable	0
CY2018	cbu	Repayment Of Subordinate Notes Payable RepaymentOfSubordinateNotesPayable	0
CY2020	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	15792000
CY2019	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	6915000
CY2018	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	6443000
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	271000
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	286000
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	298000
CY2020	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	85000
CY2019	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	6884000
CY2018	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	12561000
CY2020	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	271000
CY2019	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	286000
CY2018	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	298000
CY2020	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	87131000
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	80241000
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	71495000
CY2020	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	-1313000
CY2019	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	-3159000
CY2018	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	-1021000
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	1660012000
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-52252000
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-248107000
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	1440775000
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	-6804000
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	-9204000
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	205030000
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	211834000
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	221038000
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	1645805000
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	205030000
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	211834000
CY2020	us-gaap	Interest Paid Net InterestPaidNet	21169000
CY2019	us-gaap	Interest Paid Net InterestPaidNet	25425000
CY2018	us-gaap	Interest Paid Net InterestPaidNet	17926000
CY2020	us-gaap	Income Taxes Paid IncomeTaxesPaid	39578000
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	46457000
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	30266000
CY2020Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	22695000
CY2020	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	1291000
CY2019Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	21342000
CY2018Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	19808000
CY2020	us-gaap	Advertising Expense AdvertisingExpense	6100000
CY2019	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	2522000
CY2018	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	3299000
CY2020	us-gaap	Stock Issued1 StockIssued1	76942000
CY2019	us-gaap	Stock Issued1 StockIssued1	0
CY2018	us-gaap	Stock Issued1 StockIssued1	0
CY2020	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	547654000
CY2019	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	548856000
CY2018	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	115000
CY2020	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	529431000
CY2019	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	589733000
CY2018	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	31000
CY2020Q4	cbu	Number Of Significant Consolidated Subsidiaries Owned NumberOfSignificantConsolidatedSubsidiariesOwned	2
CY2020Q4	cbu	Number Of Unconsolidated Subsidiary Business Trusts Owned NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned	1
CY2020Q4	cbu	Number Of Customer Facilities NumberOfCustomerFacilities	232
CY2020	us-gaap	Use Of Estimates UseOfEstimates	<p style="font-family:'Times New Roman','Times','serif';font-size:10pt;font-style:italic;font-weight:bold;margin:0pt;">Critical Accounting Estimates in the Preparation of Financial Statements</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;margin:0pt 0pt 12pt 0pt;">The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Critical accounting estimates include the allowance for credit losses, actuarial assumptions associated with the pension, post-retirement and other employee benefit plans, the provision for income taxes, investment valuation, the carrying value of goodwill and other intangible assets, and acquired loan valuations.</p>
CY2020Q4	cbu	Number Of Types Of Performance Obligations NumberOfTypesOfPerformanceObligations	2
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	30300000
CY2020	cbu	Number Of Main Components Of Economic Risk NumberOfMainComponentsOfEconomicRisk	3
CY2020Q4	us-gaap	Unbilled Contracts Receivable UnbilledContractsReceivable	7700000
CY2020Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	1400000
CY2019Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	26800000
CY2019Q4	us-gaap	Unbilled Contracts Receivable UnbilledContractsReceivable	7500000
CY2019Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	1800000
CY2020Q4	us-gaap	Due From Banks DueFromBanks	7700000
CY2019Q4	us-gaap	Due From Banks DueFromBanks	10400000
CY2020Q4	us-gaap	Accrued Fees And Other Revenue Receivable AccruedFeesAndOtherRevenueReceivable	22200000
CY2020Q4	us-gaap	Other Real Estate And Foreclosed Assets OtherRealEstateAndForeclosedAssets	900000
CY2019Q4	us-gaap	Other Real Estate And Foreclosed Assets OtherRealEstateAndForeclosedAssets	1300000
CY2020Q4	us-gaap	Qualified Affordable Housing Project Investments Commitment QualifiedAffordableHousingProjectInvestmentsCommitment	900000
CY2020	us-gaap	Affordable Housing Project Investment Write Down Amount AffordableHousingProjectInvestmentWriteDownAmount	0
CY2019	us-gaap	Advertising Expense AdvertisingExpense	7100000
CY2018	us-gaap	Advertising Expense AdvertisingExpense	5100000
CY2020	us-gaap	Prior Period Reclassification Adjustment Description PriorPeriodReclassificationAdjustmentDescription	<p style="font-family:'Times New Roman','Times','serif';font-size:10pt;font-style:italic;font-weight:bold;margin:0pt;">Reclassifications</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;margin:0pt 0pt 12pt 0pt;">Certain reclassifications have been made to prior years’ balances to conform to the current year presentation.</p>
CY2019Q3	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	500000
CY2019Q3	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	95034000
CY2019Q3	us-gaap	Business Combination Consideration Transferred Equity Interests Issued And Issuable BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable	0
CY2019Q3	us-gaap	Business Combination Consideration Transferred1 BusinessCombinationConsiderationTransferred1	95034000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Cash And Equivalents BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents	90381000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets Marketable Securities BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsMarketableSecurities	39770000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Loans Acquired BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLoansAcquired	479877000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment	13970000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets Receivables BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables	1130000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Noncurrent Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets	14109000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deposits Acquired BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDepositsAcquired	568161000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Other BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther	2922000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Other Federal Home Loan Bank Advances BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOtherFederalHomeLoanBankAdvances	2420000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Subordinated Notes Payable BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesSubordinatedNotesPayable	13831000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Subordinated Debt Held By Unconsolidated Subsidiary Trusts BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts	2062000
CY2019Q3	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet	55064000
CY2019Q3	us-gaap	Goodwill Goodwill	39970000
CY2020	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	607382000
CY2019	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	626229000
CY2018	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	594174000
CY2020	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	171147000
CY2019	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	180237000
CY2018	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	167914000
CY2020Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	3427779000
CY2020Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	136901000
CY2020Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	16788000
CY2020Q4	us-gaap	Available For Sale Securities AvailableForSaleSecurities	3547892000
CY2019Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	3011551000
CY2019Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	42017000
CY2019Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	9140000
CY2019Q4	us-gaap	Available For Sale Securities AvailableForSaleSecurities	3044428000
CY2020Q4	us-gaap	Equity Securities Fv Ni Cost EquitySecuritiesFvNiCost	251000
CY2020Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Gain Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedGainBeforeTax	194000
CY2020Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Loss Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedLossBeforeTax	0
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	445000
CY2019Q4	us-gaap	Equity Securities Fv Ni Cost EquitySecuritiesFvNiCost	251000
CY2019Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Gain Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedGainBeforeTax	200000
CY2019Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Loss Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedLossBeforeTax	0
CY2019Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	451000
CY2020Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	46511000
CY2020Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Gain Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax	944000
CY2020Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Loss Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax	0
CY2020Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	47455000
CY2019Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Gain Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax	950000
CY2019Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Loss Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax	0
CY2019Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	43915000
CY2019Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	42965000
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions	117
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	913612000
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	16788000
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	3
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	14000
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	0
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	120
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	913626000
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	16788000
CY2020Q4	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	0
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost	215400000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	217938000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	732939000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	768761000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	460678000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	496977000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	1469746000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	1498001000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date Amortized Cost Basis AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis	2878763000
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate	2981677000
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	3427779000
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	3547892000
CY2020Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	2030000000.00
CY2019Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	1470000000
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49911000
CY2020Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	7355083000
CY2019Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	6840632000
CY2020Q4	us-gaap	Unamortized Loan Commitment And Origination Fees And Unamortized Discounts Or Premiums UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums	25500000
CY2019Q4	us-gaap	Unamortized Loan Commitment And Origination Fees And Unamortized Discounts Or Premiums UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums	32300000
CY2019Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	0
CY2020Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	7415952000
CY2019Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	6890543000
CY2020Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	60869000
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	17486000
CY2018Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	20661000
CY2020	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	4194000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	5720000
CY2020	us-gaap	Loans And Leases Receivable Related Parties Proceeds LoansAndLeasesReceivableRelatedPartiesProceeds	6131000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Proceeds LoansAndLeasesReceivableRelatedPartiesProceeds	8895000
CY2020Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	15549000
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	17486000
CY2019	us-gaap	Financing Receivable Nonaccrual Interest Income FinancingReceivableNonaccrualInterestIncome	0
CY2020	us-gaap	Financing Receivable Nonaccrual Interest Income FinancingReceivableNonaccrualInterestIncome	0
CY2020Q4	us-gaap	Financing Receivable Recorded Investment Nonaccrual Status FinancingReceivableRecordedInvestmentNonaccrualStatus	1500000
CY2020Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	27437000
CY2020Q4	cbu	Outstanding Loan Balances Of11 Number Of Borrowers OutstandingLoanBalancesOf11NumberOfBorrowers	800000
CY2020Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	8138000
CY2019Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	1414000
CY2020Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	35575000
CY2019Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	1414000
CY2020Q4	cbu	Impaired Financing Receivable Contractual Balance ImpairedFinancingReceivableContractualBalance	38362000
CY2019Q4	cbu	Impaired Financing Receivable Contractual Balance ImpairedFinancingReceivableContractualBalance	2944000
CY2020Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	3874000
CY2019Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	0
CY2020	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	12200000
CY2019	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	5100000
CY2018	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	7600000
CY2018	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod	0
CY2019	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod	0
CY2020	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod	0
CY2020	cbu	Customer Payment Deferral Program Deferral Period CustomerPaymentDeferralProgramDeferralPeriod	P180D
CY2020	cbu	Number Of Borrowers Representing66.5 Million In Outstanding Loan Balances NumberOfBorrowersRepresenting66.5MillionInOutstandingLoanBalances	74
CY2020Q4	cbu	Outstanding Loan Balances Of74 Number Of Borrowers OutstandingLoanBalancesOf74NumberOfBorrowers	66500000
CY2020	cbu	Percentage Of Total Loans Outstanding PercentageOfTotalLoansOutstanding	0.009
CY2020	cbu	Number Of Borrowers Representing65.7 Million In Outstanding Loan Balances NumberOfBorrowersRepresenting65.7MillionInOutstandingLoanBalances	63
CY2020Q4	cbu	Outstanding Loan Balances Of63 Number Of Borrowers OutstandingLoanBalancesOf63NumberOfBorrowers	65700000
CY2020	cbu	Number Of Borrowers Representing0.8 Million In Outstanding Loan Balances NumberOfBorrowersRepresenting0.8MillionInOutstandingLoanBalances	11
CY2020Q4	cbu	Financing Receivable Modifications Number Of Contracts FinancingReceivableModificationsNumberOfContracts	247000
CY2020Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	6984000
CY2019Q4	cbu	Financing Receivable Modifications Number Of Contracts FinancingReceivableModificationsNumberOfContracts	248000
CY2019Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	6982000
CY2020	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	55000
CY2020	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	1756000
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	73000
CY2019	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	2798000
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49911000
CY2019Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	0
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	49911000
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49284000
CY2019	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	13727000
CY2019	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	5924000
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	8430000
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49911000
CY2020Q4	cbu	Allowance For Credit Losses To Total Loans Ratio AllowanceForCreditLossesToTotalLoansRatio	0.82
CY2019	cbu	Increase Decrease In Allowance For Credit Losses To Total Loans Ratio Over The Same Quarter In Prior Year IncreaseDecreaseInAllowanceForCreditLossesToTotalLoansRatioOverTheSameQuarterInPriorYear	0.0010
CY2020	us-gaap	Financing Receivable Significant Purchases FinancingReceivableSignificantPurchases	339704000
CY2020	us-gaap	Financing Receivable Significant Sales FinancingReceivableSignificantSales	79709000
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	312434000
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	297920000
CY2020Q4	cbu	Property Plant And Equipment And Operating Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	146779000
CY2019Q4	cbu	Property Plant And Equipment And Operating Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	133282000
CY2020Q4	cbu	Property Plant And Equipment And Operating Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	165655000
CY2019Q4	cbu	Property Plant And Equipment And Operating Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	164638000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	159865000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	106925000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	52940000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	155741000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	92628000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	63113000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	12640000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	10844000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	9082000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	7551000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	6374000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	6449000
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	52940000
CY2018Q4	us-gaap	Goodwill Goodwill	733503000
CY2018	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	40307000
CY2019Q4	us-gaap	Goodwill Goodwill	773810000
CY2019	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	19898000
CY2020Q4	us-gaap	Goodwill Goodwill	793708000
CY2019Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	972000
CY2018Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	1137000
CY2020	us-gaap	Servicing Asset At Amortized Value Additions ServicingAssetAtAmortizedValueAdditions	715000
CY2019	us-gaap	Servicing Asset At Amortized Value Additions ServicingAssetAtAmortizedValueAdditions	17000
CY2020	cbu	Servicing Asset At Amortized Cost Increase Due To Business Acquisition ServicingAssetAtAmortizedCostIncreaseDueToBusinessAcquisition	122000
CY2019	cbu	Servicing Asset At Amortized Cost Increase Due To Business Acquisition ServicingAssetAtAmortizedCostIncreaseDueToBusinessAcquisition	196000
CY2020	us-gaap	Servicing Asset At Amortized Value Amortization1 ServicingAssetAtAmortizedValueAmortization1	379000
CY2019	us-gaap	Servicing Asset At Amortized Value Amortization1 ServicingAssetAtAmortizedValueAmortization1	378000
CY2020Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	1430000
CY2019Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	972000
CY2019Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	298000
CY2018Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	0
CY2020	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Provisions ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisions	150000
CY2019	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Provisions ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisions	326000
CY2020	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Recoveries ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRecoveries	229000
CY2019	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Recoveries ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRecoveries	28000
CY2020Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	219000
CY2019Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	298000
CY2020Q4	cbu	Servicing Asset At Amortized Cost Net ServicingAssetAtAmortizedCostNet	1211000
CY2019Q4	cbu	Servicing Asset At Amortized Cost Net ServicingAssetAtAmortizedCostNet	674000
CY2020Q4	us-gaap	Servicing Asset At Amortized Value Fair Value ServicingAssetAtAmortizedValueFairValue	1384000
CY2019Q4	us-gaap	Servicing Asset At Amortized Value Fair Value ServicingAssetAtAmortizedValueFairValue	1362000
CY2020	us-gaap	Mortgage Loans On Real Estate Cost Of Mortgages Sold MortgageLoansOnRealEstateCostOfMortgagesSold	79709000
CY2019	us-gaap	Mortgage Loans On Real Estate Cost Of Mortgages Sold MortgageLoansOnRealEstateCostOfMortgagesSold	2204000
CY2020Q4	cbu	Mortgage Loans Serviced For Others MortgageLoansServicedForOthers	351759000
CY2019Q4	cbu	Mortgage Loans Serviced For Others MortgageLoansServicedForOthers	294093000
CY2020Q4	cbu	Custodial Escrow Balances Maintained In Connection With Loans Serviced For Others CustodialEscrowBalancesMaintainedInConnectionWithLoansServicedForOthers	5583000
CY2019Q4	cbu	Custodial Escrow Balances Maintained In Connection With Loans Serviced For Others CustodialEscrowBalancesMaintainedInConnectionWithLoansServicedForOthers	4596000
CY2020	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Weighted Average Life1 ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1	P21Y6M
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Weighted Average Life1 ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1	P20Y10M24D
CY2020	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed	0.304
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed	0.187
CY2020	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Discount Rate ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate	0.021
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Discount Rate ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate	0.030
CY2020Q4	us-gaap	Noninterest Bearing Domestic Deposit Checking NoninterestBearingDomesticDepositChecking	3361768000
CY2019Q4	us-gaap	Noninterest Bearing Domestic Deposit Checking NoninterestBearingDomesticDepositChecking	2465902000
CY2020Q4	us-gaap	Interest Bearing Domestic Deposit Checking InterestBearingDomesticDepositChecking	2876420000
CY2019Q4	us-gaap	Interest Bearing Domestic Deposit Checking InterestBearingDomesticDepositChecking	2138348000
CY2020Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1949517000
CY2019Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1538203000
CY2020Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	2103498000
CY2019Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	1916385000
CY2020Q4	us-gaap	Time Deposits TimeDeposits	933771000
CY2019Q4	us-gaap	Time Deposits TimeDeposits	936129000
CY2020Q4	us-gaap	Deposits Deposits	11224974000
CY2019Q4	us-gaap	Deposits Deposits	8994967000
CY2020	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	2182000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	3678000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	1796000
CY2020	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	665000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	942000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	858000
CY2020	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	2685000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	5836000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	3638000
CY2020	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	11229000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	10004000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	4366000
CY2020	us-gaap	Interest Expense Deposits InterestExpenseDeposits	16761000
CY2019	us-gaap	Interest Expense Deposits InterestExpenseDeposits	20460000
CY2018	us-gaap	Interest Expense Deposits InterestExpenseDeposits	10658000
CY2020Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	570039000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More Next Twelve Months TimeDepositsMaturities250000OrMoreNextTwelveMonths	140887000
CY2020Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	126106000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More Year Two TimeDepositsMaturities250000OrMoreYearTwo	7182000
CY2020Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	106713000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More Year Three TimeDepositsMaturities250000OrMoreYearThree	6632000
CY2020Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	109573000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More Year Four TimeDepositsMaturities250000OrMoreYearFour	22310000
CY2020Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	21244000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More Year Five TimeDepositsMaturities250000OrMoreYearFive	2595000
CY2020Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	96000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More After Year Five TimeDepositsMaturities250000OrMoreAfterYearFive	0
CY2020Q4	us-gaap	Time Deposits TimeDeposits	933771000
CY2020Q4	cbu	Time Deposits Maturities250000 Or More TimeDepositsMaturities250000OrMore	179606000
CY2020Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	0
CY2019Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	8300000
CY2020Q4	us-gaap	Debt Instrument Unamortized Discount Premium Net DebtInstrumentUnamortizedDiscountPremiumNet	303000
CY2019Q4	us-gaap	Debt Instrument Unamortized Discount Premium Net DebtInstrumentUnamortizedDiscountPremiumNet	795000
CY2020Q4	us-gaap	Junior Subordinated Notes JuniorSubordinatedNotes	3303000
CY2019Q4	us-gaap	Junior Subordinated Notes JuniorSubordinatedNotes	13795000
CY2020Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	77320000
CY2019Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	77320000
CY2020Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	284008000
CY2019Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	241708000
CY2020Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	6658000
CY2019Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	3750000
CY2020Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	371289000
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	344873000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	44347000
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	2122000
CY2020	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-331000
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-1603000
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	541000
CY2020Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	371289000
CY2020Q4	us-gaap	Debt Weighted Average Interest Rate DebtWeightedAverageInterestRate	0.0076
CY2020	us-gaap	Long Term Debt Weighted Average Interest Rate Over Time LongTermDebtWeightedAverageInterestRateOverTime	0.0127
CY2019	us-gaap	Long Term Debt Weighted Average Interest Rate Over Time LongTermDebtWeightedAverageInterestRateOverTime	0.0186
CY2020Q4	cbu	Number Of Unconsolidated Subsidiary Business Trusts Owned NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned	1
CY2020	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	35728000
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	34804000
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	32504000
CY2020	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	8008000
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	7773000
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	9180000
CY2020	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-2005000
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-699000
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	41400000
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	40275000
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	15004000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	12059000
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	7552000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	5393000
CY2020Q4	cbu	Deferred Tax Assets Tax Deferred Expense Operating Lease Liabilities DeferredTaxAssetsTaxDeferredExpenseOperatingLeaseLiabilities	8601000
CY2019Q4	cbu	Deferred Tax Assets Tax Deferred Expense Operating Lease Liabilities DeferredTaxAssetsTaxDeferredExpenseOperatingLeaseLiabilities	9801000
CY2020Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	900000
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	837000
CY2020Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	32057000
CY2019Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	28090000
CY2020Q4	cbu	Deferred Tax Liabilities Unrealized Gains On Investment Securities DeferredTaxLiabilitiesUnrealizedGainsOnInvestmentSecurities	43325000
CY2019Q4	cbu	Deferred Tax Liabilities Unrealized Gains On Investment Securities DeferredTaxLiabilitiesUnrealizedGainsOnInvestmentSecurities	21547000
CY2020Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Goodwill DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill	40802000
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Goodwill DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill	39189000
CY2020Q4	cbu	Deferred Tax Liabilities Right Of Use Assets DeferredTaxLiabilitiesRightOfUseAssets	8384000
CY2019Q4	cbu	Deferred Tax Liabilities Right Of Use Assets DeferredTaxLiabilitiesRightOfUseAssets	9566000
CY2020Q4	cbu	Deferred Tax Liabilities Deferred Expense Deferred Loan Origination Costs DeferredTaxLiabilitiesDeferredExpenseDeferredLoanOriginationCosts	7904000
CY2019Q4	cbu	Deferred Tax Liabilities Deferred Expense Deferred Loan Origination Costs DeferredTaxLiabilitiesDeferredExpenseDeferredLoanOriginationCosts	7639000
CY2020Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	3089000
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	2736000
CY2020Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	291000
CY2019Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	162000
CY2020Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	16987000
CY2019Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	13769000
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	120782000
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	94608000
CY2020Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	88725000
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	66518000
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.025
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.034
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.008
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.016
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.009
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
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
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.015
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.015
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.016
CY2020	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.030
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.013
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.013
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.014
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.003
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.003
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.201
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.192
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.208
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	24000
CY2020	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	0
CY2019	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	0
CY2018	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	24000
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2020Q4	us-gaap	Statutory Accounting Practices Statutory Amount Available For Dividend Payments StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPayments	110700000
CY2020Q4	cbu	Bank Capital And Surplus Transferable To Company Maximum BankCapitalAndSurplusTransferableToCompanyMaximum	0.10
CY2020Q4	cbu	Aggregate Bank Capital And Surplus Transferable To Company Maximum AggregateBankCapitalAndSurplusTransferableToCompanyMaximum	0.20
CY2020	cbu	Defined Benefit Plan Additional Unamortized Actuarial Gain Loss DefinedBenefitPlanAdditionalUnamortizedActuarialGainLoss	1100000
CY2009	cbu	Other Comprehensive Income Loss Negative Postretirement Medical Plan Amendment Net Of Tax OtherComprehensiveIncomeLossNegativePostretirementMedicalPlanAmendmentNetOfTax	3500000
CY2020	cbu	Maximum Percentage Of Pension Gain Loss Not Amortized MaximumPercentageOfPensionGainLossNotAmortized	0.10
CY2020Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	1400000
CY2011Q2	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized	900000
CY2014Q2	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized	1000000
CY2017Q2	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized	1000000
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	800000
CY2020Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Outstanding Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions	1542259
CY2020Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Exercise Price Beginning Balance1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1	45.49
CY2020	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Remaining Contractual Term2 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2	P5Y11M8D
CY2020Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Exercisable Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions	978833
CY2020Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Exercise Price1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1	40.77
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P5Y11M8D
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P4Y8M26D
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	25900000
CY2020Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	21100000
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsMethodUsed	Black-Scholes option-pricing model
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	10.86
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	14.16
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	13.44
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y6M
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y6M
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y6M
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0257
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0273
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0291
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2929
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2931
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2944
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0067
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0244
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0282
CY2020	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	600000
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	500000
CY2018	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	400000
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2020	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-514000
CY2019	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-400000
CY2018	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-744000
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	164162000
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	168663000
CY2018	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	167897000
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	52969000
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51732000
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51165000
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.10
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.26
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.28
CY2020	us-gaap	Net Income Loss NetIncomeLoss	164676000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2020	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-514000
CY2019	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-400000
CY2018	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-744000
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	164162000
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	168663000
CY2018	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	167897000
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	52969000
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51732000
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51165000
CY2020	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	352000
CY2019	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	516000
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	583000
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	53321000
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	52248000
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	51748000
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.08
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.23
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.24
CY2020	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.66
CY2019	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.58
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.44
CY2020Q4	us-gaap	Stock Repurchase Program Number Of Shares Authorized To Be Repurchased StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased	2600000
CY2020	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	0
CY2019Q4	us-gaap	Stock Repurchase Program Number Of Shares Authorized To Be Repurchased StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased	2680000
CY2020Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Face Amount Liability FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability	1352781000
CY2019Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Face Amount Liability FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability	1181652000
CY2020Q4	us-gaap	Line Of Credit Facility Current Borrowing Capacity LineOfCreditFacilityCurrentBorrowingCapacity	25000000.0
CY2020Q4	us-gaap	Federal Home Loan Bank Advances General Debt Obligations Disclosures Amount Of Available Unused Funds FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds	1660000000
CY2020Q4	cbu	Federal Reserve Advances General Debt Obligations Disclosures Amount Of Available Unused Funds FederalReserveAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds	256200000
CY2020	us-gaap	Litigation Settlement Expense LitigationSettlementExpense	3000000.0
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	8697000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	7505000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	6336000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	4973000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	3688000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	8222000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	39421000
CY2020Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	3564000
CY2020	cbu	Lessee Operating Lease Option To Terminate Term LesseeOperatingLeaseOptionToTerminateTerm	P1Y
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	35857000
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	40913000
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	9000000
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	8724000
CY2020	us-gaap	Variable Lease Cost VariableLeaseCost	53000
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	18000
CY2020	us-gaap	Short Term Lease Cost ShortTermLeaseCost	369000
CY2019	us-gaap	Short Term Lease Cost ShortTermLeaseCost	240000
CY2020	us-gaap	Lease Cost LeaseCost	9422000
CY2019	us-gaap	Lease Cost LeaseCost	8982000
CY2018	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	9000000.0
CY2020Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy TierOneLeverageCapitalRequiredForCapitalAdequacy	517736000
CY2020Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	4.00
CY2020Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized TierOneLeverageCapitalRequiredToBeWellCapitalized	647169000
CY2020Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	5.00
CY2020Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	1314864000
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	8478000
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	7938000
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	3519000
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	14145000
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	34908000
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	39895000
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0282
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0295
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	35857000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	9396000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	7952000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	6664000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	5695000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	4565000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	11150000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	45422000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	4509000
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	40913000
CY2020Q4	cbu	Required Capital Conservation Ratio RequiredCapitalConservationRatio	0.0250
CY2020Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.070
CY2020Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.085
CY2020Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.105
CY2020Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	1314864000
CY2020Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	10.16
CY2020Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	18.99
CY2020Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy TierOneRiskBasedCapitalRequiredForCapitalAdequacy	415472000
CY2020Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	6.00
CY2020Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	588585000
CY2020Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.0850
CY2020Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized TierOneRiskBasedCapitalRequiredToBeWellCapitalized	553962000
CY2020Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	8.00
CY2020Q4	us-gaap	Capital Capital	1375704000
CY2020Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	19.87
CY2020Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	553962000
CY2020Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	8.00
CY2020Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer CapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	727075000
CY2020Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.1050
CY2020Q4	us-gaap	Capital Required To Be Well Capitalized CapitalRequiredToBeWellCapitalized	692453000
CY2020Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	10.00
CY2020Q4	us-gaap	Common Equity Tier One Capital CommonEquityTierOneCapital	1239754000
CY2020Q4	us-gaap	Common Equity Tier One Capital Ratio CommonEquityTierOneCapitalRatio	17.90
CY2020Q4	us-gaap	Common Equity Tier One Capital Required For Capital Adequacy CommonEquityTierOneCapitalRequiredForCapitalAdequacy	311604000
CY2020Q4	cbu	Common Equity Tier1 Capital Required For Capital Adequacy Ratio CommonEquityTier1CapitalRequiredForCapitalAdequacyRatio	0.0450
CY2020Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	484717000
CY2020Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.0700
CY2020Q4	us-gaap	Common Equity Tier One Capital Required To Be Well Capitalized CommonEquityTierOneCapitalRequiredToBeWellCapitalized	450094000
CY2020Q4	cbu	Common Equity Tier1 Capital Required To Be Well Capitalized Ratio CommonEquityTier1CapitalRequiredToBeWellCapitalizedRatio	0.0650
CY2019Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	1148336000
CY2019Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	10.80
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy TierOneLeverageCapitalRequiredForCapitalAdequacy	425431000
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	4.00
CY2019Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized TierOneLeverageCapitalRequiredToBeWellCapitalized	531788000
CY2019Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	5.00
CY2019Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	1148336000
CY2019Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	17.23
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy TierOneRiskBasedCapitalRequiredForCapitalAdequacy	399834000
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	6.00
CY2019Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	566432000
CY2019Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.0850
CY2019Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized TierOneRiskBasedCapitalRequiredToBeWellCapitalized	533112000
CY2019Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	8.00
CY2019Q4	us-gaap	Capital Capital	1198724000
CY2019Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	17.99
CY2019Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	533112000
CY2019Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	8.00
CY2019Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer CapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	699710000
CY2019Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.1050
CY2019Q4	us-gaap	Capital Required To Be Well Capitalized CapitalRequiredToBeWellCapitalized	666390000
CY2019Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	10.00
CY2019Q4	us-gaap	Common Equity Tier One Capital CommonEquityTierOneCapital	1073281000
CY2019Q4	us-gaap	Common Equity Tier One Capital Ratio CommonEquityTierOneCapitalRatio	16.11
CY2019Q4	us-gaap	Common Equity Tier One Capital Required For Capital Adequacy CommonEquityTierOneCapitalRequiredForCapitalAdequacy	299876000
CY2019Q4	cbu	Common Equity Tier1 Capital Required For Capital Adequacy Ratio CommonEquityTier1CapitalRequiredForCapitalAdequacyRatio	0.0450
CY2019Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	466473000
CY2019Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.0700
CY2019Q4	us-gaap	Common Equity Tier One Capital Required To Be Well Capitalized CommonEquityTierOneCapitalRequiredToBeWellCapitalized	433154000
CY2019Q4	cbu	Common Equity Tier1 Capital Required To Be Well Capitalized Ratio CommonEquityTier1CapitalRequiredToBeWellCapitalizedRatio	0.0650
CY2020Q4	us-gaap	Fair Value Assets Level1 To Level2 Transfers Amount FairValueAssetsLevel1ToLevel2TransfersAmount	0
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15956000
CY2019	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	8608000
CY2019	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	347462000
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	209338000
CY2019Q4	us-gaap	Assets Assets	11410295000
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	1588000
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	1074000
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	851000
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	586000
CY2020	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	368403000
CY2020	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	14212000
CY2020	us-gaap	Noninterest Income NoninterestIncome	228419000
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	14297000
CY2020	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	4933000
CY2020	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	357304000
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	206076000
CY2020Q4	us-gaap	Assets Assets	13931094000
CY2020Q4	us-gaap	Goodwill Goodwill	793708000
CY2020Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	52940000
CY2019	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	359175000
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	8430000
CY2019	us-gaap	Noninterest Income NoninterestIncome	230619000
CY2019Q4	us-gaap	Goodwill Goodwill	773810000
CY2019Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	63113000
CY2018	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	345055000
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10837000
CY2018	us-gaap	Noninterest Income NoninterestIncome	224059000
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	18155000
CY2018	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	-769000
CY2018	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	327903000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	212988000
CY2018Q4	us-gaap	Assets Assets	10607295000
CY2018Q4	us-gaap	Goodwill Goodwill	733503000
CY2018Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	73846000

Files In Submission

Name	View Source	Status
0001104659-21-030055-index-headers.html	Edgar Link	pending
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$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

2019 Q4 Form 10-K Financial Statement

#000110465921030055 Filed on March 01, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$CBU COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

2019 Q4 Form 10-K Financial Statement

#000110465921030055 Filed on March 01, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu