$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

$cbu Overview Financials Valuation SEC Filings Company Website

2018 Q4 Form 10-K Financial Statement

#000114036120004510 Filed on March 02, 2020

Income Statement

Concept	2018 Q4	2017 Q4	2017
Revenue			$329.5M
YoY Change
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development			$37.58M
YoY Change
% of Gross Profit
Depreciation & Amortization	$8.300M	$9.000M	$16.02M
YoY Change	-7.78%	76.47%	-21.45%
% of Gross Profit
Operating Expenses			$37.58M
YoY Change
Operating Profit
YoY Change
Interest Expense			$13.78M
YoY Change
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$51.50M	$47.60M	$160.0M
YoY Change	8.19%	20.2%	3.47%
Income Tax	$10.70M	$13.60M	$9.248M
% Of Pretax Income	20.78%	28.57%	5.78%
Net Earnings	$40.80M	$72.00M	$150.7M
YoY Change	-43.33%	172.73%	45.2%
Net Earnings / Revenue			45.75%
Basic Earnings Per Share			$3.07
Diluted Earnings Per Share	$786.1K	$1.401M	$3.03
COMMON SHARES
Basic Shares Outstanding			48.84M
Diluted Shares Outstanding			49.47M

Balance Sheet

Concept	2018 Q4	2017 Q4	2017
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$211.8M	$221.0M
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	$120.0M	$123.0M	$123.0M
YoY Change	-2.45%	9.82%	9.82%
Goodwill	$733.5M	$734.4M
YoY Change	-0.13%
Intangibles	$73.85M	$90.66M
YoY Change	-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	$10.61B	$10.75B	$10.75B
YoY Change	-1.29%	24.0%	24.0%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$157.0M	$181.0M	$181.0M
YoY Change	-13.26%	25.69%	25.69%
Accrued Expenses
YoY Change
Deferred Revenue
YoY Change
Short-Term Debt	$259.0M	$337.0M	$337.0M
YoY Change	-23.15%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$157.0M	$181.0M	$181.0M
YoY Change	-13.26%	25.69%	25.69%
LONG-TERM LIABILITIES
Long-Term Debt	$98.00M	$123.0M	$123.0M
YoY Change	-20.33%	20.59%	20.59%
Other Long-Term Liabilities
YoY Change
Total Long-Term Liabilities	$98.00M	$123.0M	$123.0M
YoY Change	-20.33%	20.59%	20.59%
TOTAL LIABILITIES
Total Short-Term Liabilities	$157.0M	$181.0M	$181.0M
Total Long-Term Liabilities	$98.00M	$123.0M	$123.0M
Total Liabilities	$8.894B	$9.111B	$9.111B
YoY Change	-2.39%	22.0%	22.0%
SHAREHOLDERS EQUITY
Retained Earnings	$795.6M
YoY Change
Common Stock
YoY Change
Preferred Stock
YoY Change
Treasury Stock (at cost)	$11.53M
YoY Change
Treasury Stock Shares	$319.0K
Shareholders Equity	$1.714B	$1.635B	$1.635B
YoY Change
Total Liabilities & Shareholders Equity	$10.61B	$10.75B	$10.75B
YoY Change	-1.29%	24.0%	24.0%

Cashflow Statement

Concept	2018 Q4	2017 Q4	2017
OPERATING ACTIVITIES
Net Income	$40.80M	$72.00M	$150.7M
YoY Change	-43.33%	172.73%	45.2%
Depreciation, Depletion And Amortization	$8.300M	$9.000M	$16.02M
YoY Change	-7.78%	76.47%	-21.45%
Cash From Operating Activities	$53.60M	$50.80M	$189.7M
YoY Change	5.51%	58.75%	39.67%
INVESTING ACTIVITIES
Capital Expenditures	-$3.700M	-$3.100M	$10.82M
YoY Change	19.35%	-32.61%	-187.25%
Acquisitions			$107.4M
YoY Change
Other Investing Activities	$20.90M	$58.90M	$142.2M
YoY Change	-64.52%	-520.71%	-229.74%
Cash From Investing Activities	$17.20M	$55.80M	$131.4M
YoY Change	-69.18%	-401.62%	-207.68%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net			-$1.257M
YoY Change			-107.86%
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-115.8M	-127.1M	-273.9M
YoY Change	-8.89%	11454.55%	-4069.04%
NET CHANGE
Cash From Operating Activities	53.60M	50.80M	189.7M
Cash From Investing Activities	17.20M	55.80M	131.4M
Cash From Financing Activities	-115.8M	-127.1M	-273.9M
Net Change In Cash	-45.00M	-20.50M	47.18M
YoY Change	119.51%	-265.32%	127.93%
FREE CASH FLOW
Cash From Operating Activities	$53.60M	$50.80M	$189.7M
Capital Expenditures	-$3.700M	-$3.100M	$10.82M
Free Cash Flow	$57.30M	$53.90M	$178.9M
YoY Change	6.31%	47.27%	20.68%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value
CY2019	dei	Amendment Flag AmendmentFlag	false
CY2019	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2019	dei	Entity Registrant Name EntityRegistrantName	COMMUNITY BANK SYSTEM, INC.
CY2019	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2019
CY2019	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2019	dei	Entity Central Index Key EntityCentralIndexKey	0000723188
CY2019Q4	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	cbu:AccruedInterestAndOtherLiabilities
CY2019	dei	Document Type DocumentType	10-K
CY2019	dei	Document Annual Report DocumentAnnualReport	true
CY2019	dei	Document Period End Date DocumentPeriodEndDate	2019-12-31
CY2019	dei	Document Transition Report DocumentTransitionReport	false
CY2019	dei	Entity File Number EntityFileNumber	001-13695
CY2019	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2019	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	16-1213679
CY2019	dei	Entity Address Address Line1 EntityAddressAddressLine1	5790 Widewaters Parkway
CY2019	dei	Entity Address City Or Town EntityAddressCityOrTown	DeWitt
CY2019	dei	Entity Address State Or Province EntityAddressStateOrProvince	NY
CY2019	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	13214
CY2019	dei	City Area Code CityAreaCode	315
CY2019	dei	Local Phone Number LocalPhoneNumber	445-2282
CY2019	dei	Security12b Title Security12bTitle	Common Stock, $1.00 par value per share
CY2019	dei	Trading Symbol TradingSymbol	CBU
CY2019	dei	Security Exchange Name SecurityExchangeName	NYSE
CY2019	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2019	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2019	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2019	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2019	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2019	dei	Entity Small Business EntitySmallBusiness	false
CY2019	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2019	dei	Entity Shell Company EntityShellCompany	false
CY2019Q2	dei	Entity Public Float EntityPublicFloat	3341455914
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CY2019Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	3011551000
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CY2019Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	42965000
CY2018Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	44678000
CY2019Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	43915000
CY2018Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	45609000
CY2019Q4	us-gaap	Loans Receivable Held For Sale Net Not Part Of Disposal Group LoansReceivableHeldForSaleNetNotPartOfDisposalGroup	0
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CY2018Q4	cbu	Core Deposit Intangibles Net CoreDepositIntangiblesNet	18596000
CY2019Q4	cbu	Other Finite Lived Intangible Assets Net OtherFiniteLivedIntangibleAssetsNet	46695000
CY2018Q4	cbu	Other Finite Lived Intangible Assets Net OtherFiniteLivedIntangibleAssetsNet	55250000
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CY2018Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	6009555000
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CY2018Q4	us-gaap	Deposits Deposits	8322371000
CY2019Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	8300000
CY2018Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	54400000
CY2019Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	241708000
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CY2019Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies
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CY2017	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	25986000
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	24090000
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	21471000
CY2017	us-gaap	Other Noninterest Expense OtherNoninterestExpense	22609000
CY2019	us-gaap	Noninterest Expense NoninterestExpense	372026000
CY2018	us-gaap	Noninterest Expense NoninterestExpense	345289000
CY2017	us-gaap	Noninterest Expense NoninterestExpense	347149000
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
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	159965000
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	40275000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	44347000
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9248000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.26
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.28
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.07
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.23
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.24
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.03
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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	707000
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	605000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	3087000
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	263000
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
CY2017	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerBeforeTax	1858000
CY2019	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerTax	-0
CY2018	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerTax	-0
CY2017	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerTax	711000
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	444000
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
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
CY2017	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	-859000
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
CY2017	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditTax	-324000
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
CY2017	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	-535000
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
CY2017	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 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
CY2017	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 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
CY2017	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 Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerBeforeTax	0
CY2018	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerBeforeTax	0
CY2019	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger After Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerAfterTax	0
CY2018	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger After Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerAfterTax	0
CY2017	cbu	Other Comprehensive Income Loss Defined Benefit Plan Gain Loss Arising During Period Due To Plan Merger After Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossArisingDuringPeriodDueToPlanMergerAfterTax	1147000
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
CY2017	us-gaap	Other Comprehensive Income Defined Benefit Plans Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent	-168000
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
CY2017	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	-17851000
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
CY2017	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	-6787000
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
CY2017	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	-11064000
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
CY2017	cbu	Other Comprehensive Income Reclassification Adjustment For Equity Securities Net Of Tax OtherComprehensiveIncomeReclassificationAdjustmentForEquitySecuritiesNetOfTax	0
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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	2000
CY2017Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax Effect AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTaxEffect	-7044000
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	34882000
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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	1000
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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	1000
CY2019	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	37124000
CY2018	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-30402000
CY2017	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-11065000
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
CY2017	cbu	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent Including Cumulative Effect Of Change In Accounting Principle OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParentIncludingCumulativeEffectOfChangeInAccountingPrinciple	-10897000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	204142000
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	127035000
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	139820000
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
CY2017Q4	cbu	Accumulated Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Gross Of Tax AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansGrossOfTax	28677000
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
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	32837000
CY2017Q4	us-gaap	Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax	21633000
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
CY2017Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Gross AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentGross	23940000
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
CY2017Q4	cbu	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Tax Effect AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentTaxEffect	6006000
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
CY2017Q4	us-gaap	Accumulated Other Comprehensive Income Loss Available For Sale Securities Adjustment Net Of Tax AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax	17934000
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	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-3699000
CY2016Q4	us-gaap	Stockholders Equity StockholdersEquity	1198100000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-10897000
CY2017	us-gaap	Tax Cuts And Jobs Act Of2017 Reclassification From Aoci To Retained Earnings Tax Effect TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect	0
CY2017	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.32
CY2017	us-gaap	Dividends Common Stock DividendsCommonStock	65497000
CY2017	cbu	Stock Issued During Period Value Employee Stock Ownership Plan Net Of Impact Of Net Settlement Of Tax Withholding Obligations StockIssuedDuringPeriodValueEmployeeStockOwnershipPlanNetOfImpactOfNetSettlementOfTaxWithholdingObligations	4563000
CY2017	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	5137000
CY2017	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	343132000
CY2017	cbu	Deferred Compensation Arrangements Value Acquired DeferredCompensationArrangementsValueAcquired	0
CY2017	cbu	Treasury Stock Value Acquired And Issued To Deferred Compensation Arrangements Cost Method TreasuryStockValueAcquiredAndIssuedToDeferredCompensationArrangementsCostMethod	-0
CY2017	us-gaap	Stock Issued During Period Value Employee Benefit Plan StockIssuedDuringPeriodValueEmployeeBenefitPlan	10060000
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
CY2017Q4	us-gaap	Cumulative Effect Of New Accounting Principle In Period Of Adoption CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	0
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	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	5285000
CY2019	cbu	Stock Issued During Period Value Deferred Compensation Arrangements StockIssuedDuringPeriodValueDeferredCompensationArrangements	0
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
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
CY2019	us-gaap	Depreciation Depreciation	15891000
CY2018	us-gaap	Depreciation Depreciation	15749000
CY2017	us-gaap	Depreciation Depreciation	16024000
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	15956000
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	18155000
CY2017	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	16941000
CY2019	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	6176000
CY2018	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	9404000
CY2017	cbu	Accretion Amortization On Investments Loans And Borrowings AccretionAmortizationOnInvestmentsLoansAndBorrowings	6619000
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	5285000
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	6064000
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	5137000
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	8430000
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10837000
CY2017	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10984000
CY2019	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	2302000
CY2018	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	-2663000
CY2017	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	28692000
CY2019	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	378000
CY2018	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-10252000
CY2017	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-26090000
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
CY2018	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	449000
CY2017	us-gaap	Amortization Of Mortgage Servicing Rights Ms Rs AmortizationOfMortgageServicingRightsMSRs	499000
CY2019	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	19000
CY2018	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	657000
CY2017	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-0
CY2019	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-0
CY2018	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-318000
CY2017	us-gaap	Gains Losses On Extinguishment Of Debt GainsLossesOnExtinguishmentOfDebt	-0
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1678000
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1579000
CY2017	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	1586000
CY2019	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	4882000
CY2018	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	-0
CY2017	us-gaap	Marketable Securities Realized Gain Loss MarketableSecuritiesRealizedGainLoss	2000
CY2019	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	-11000
CY2018	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	80000
CY2017	cbu	Net Gain Loss On Sale Of Loans And Other Assets NetGainLossOnSaleOfLoansAndOtherAssets	-181000
CY2019	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-2545000
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	189674000
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
CY2017	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	0
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
CY2017	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	157278000
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
CY2017	us-gaap	Proceeds From Maturities Prepayments And Calls Of Other Investments ProceedsFromMaturitiesPrepaymentsAndCallsOfOtherInvestments	30116000
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
CY2017	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	90380000
CY2019	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	202000
CY2018	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	31000
CY2017	cbu	Payments To Acquire Equity And Other Securities PaymentsToAcquireEquityAndOtherSecurities	13302000
CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	140382000
CY2018	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	35414000
CY2017	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	-164846000
CY2019	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	90381000
CY2018	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	16000
CY2017	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	52132000
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
CY2017	us-gaap	Payments To Acquire Businesses Net Of Cash Acquired PaymentsToAcquireBusinessesNetOfCashAcquired	107414000
CY2019	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	1597000
CY2018	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	0
CY2017	cbu	Settlement Of Bank Owned Life Insurance Policies SettlementOfBankOwnedLifeInsurancePolicies	1779000
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	5686000
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	12646000
CY2017	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	10819000
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
CY2017	us-gaap	Payments For Proceeds From Real Estate Partnership Investment Net PaymentsForProceedsFromRealEstatePartnershipInvestmentNet	733000
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
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	131371000
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	104435000
CY2018	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	-122049000
CY2017	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	-79940000
CY2019	us-gaap	Repayments Of Debt RepaymentsOfDebt	646000
CY2018	us-gaap	Repayments Of Debt RepaymentsOfDebt	95000
CY2017	us-gaap	Repayments Of Debt RepaymentsOfDebt	81544000
CY2019	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-64405000
CY2018	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-47339000
CY2017	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-144809000
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
CY2017	cbu	Repayments Of Subordinated Debt Held By Unconsolidated Subsidiary Trusts RepaymentsOfSubordinatedDebtHeldByUnconsolidatedSubsidiaryTrusts	-0
CY2019	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	6915000
CY2018	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	6443000
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	4563000
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	286000
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	298000
CY2017	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	3306000
CY2019	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	6884000
CY2018	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	12561000
CY2017	us-gaap	Proceeds From Sale Of Treasury Stock ProceedsFromSaleOfTreasuryStock	10060000
CY2019	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	286000
CY2018	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	298000
CY2017	us-gaap	Increase Decrease In Deferred Compensation IncreaseDecreaseInDeferredCompensation	3306000
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	80241000
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	71495000
CY2017	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	62305000
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
CY2017	us-gaap	Excess Tax Benefit From Share Based Compensation Financing Activities ExcessTaxBenefitFromShareBasedCompensationFinancingActivities	-1433000
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
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-273864000
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
CY2017	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	47181000
CY2018Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	211834000
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	221038000
CY2016Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	173857000
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
CY2019	us-gaap	Interest Paid Net InterestPaidNet	25425000
CY2018	us-gaap	Interest Paid Net InterestPaidNet	17926000
CY2017	us-gaap	Interest Paid Net InterestPaidNet	13705000
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	46457000
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	30266000
CY2017	us-gaap	Income Taxes Paid IncomeTaxesPaid	41231000
CY2019Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	21342000
CY2018Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	19808000
CY2017Q4	us-gaap	Dividends Payable Current And Noncurrent DividendsPayableCurrentAndNoncurrent	17460000
CY2019	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	2522000
CY2018	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	3299000
CY2017	us-gaap	Transfer To Other Real Estate TransferToOtherRealEstate	3518000
CY2019	us-gaap	Stock Issued1 StockIssued1	0
CY2018	us-gaap	Stock Issued1 StockIssued1	0
CY2017	us-gaap	Stock Issued1 StockIssued1	343132000
CY2019	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	548856000
CY2018	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	115000
CY2017	us-gaap	Fair Value Of Assets Acquired FairValueOfAssetsAcquired	1961246000
CY2019	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	589733000
CY2018	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	31000
CY2017	us-gaap	Liabilities Assumed1 LiabilitiesAssumed1	1870449000
CY2019Q4	cbu	Number Of Significant Consolidated Subsidiaries Owned NumberOfSignificantConsolidatedSubsidiariesOwned	2
CY2019Q4	cbu	Number Of Unconsolidated Subsidiary Business Trusts Owned NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned	1
CY2019Q4	cbu	Number Of Customer Facilities NumberOfCustomerFacilities	231
CY2019	us-gaap	Use Of Estimates UseOfEstimates	<span style="color: #000000; font-family: 'Times New Roman'; font-size: 10pt; font-style: italic; font-weight: bold;">Critical Accounting Estimates in the Preparation of Financial Statements</span> <div style="text-align: left; color: #000000; font-family: 'Times New Roman'; font-size: 10pt;">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 loan losses, actuarial assumptions associated with the pension, post-retirement and other employee benefit plans, the provision for income taxes, investment valuation and other-than-temporary impairment, the carrying value of goodwill and other intangible assets, and acquired loan valuations.</div>
CY2019	cbu	Number Of Main Components Of Economic Risk NumberOfMainComponentsOfEconomicRisk	3
CY2019Q4	cbu	Number Of Types Of Performance Obligations NumberOfTypesOfPerformanceObligations	2
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
CY2018Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	26400000
CY2018Q4	us-gaap	Unbilled Contracts Receivable UnbilledContractsReceivable	7800000
CY2018Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	2200000
CY2019Q4	us-gaap	Due From Banks DueFromBanks	10400000
CY2018Q4	us-gaap	Due From Banks DueFromBanks	15000000.0
CY2019	cbu	Number Of Days Past Due For Loans To Be Placed On Nonaccrual Status NumberOfDaysPastDueForLoansToBePlacedOnNonaccrualStatus	P90D
CY2019	cbu	Period For Which Nonaccrual Tdr Loan Remains On Nonaccrual Status PeriodForWhichNonaccrualTDRLoanRemainsOnNonaccrualStatus	P12M
CY2019Q4	us-gaap	Other Real Estate And Foreclosed Assets OtherRealEstateAndForeclosedAssets	1300000
CY2018Q4	us-gaap	Other Real Estate And Foreclosed Assets OtherRealEstateAndForeclosedAssets	1300000
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
CY2019	cbu	Number Of Broad Components Used In Allowance Methodology NumberOfBroadComponentsUsedInAllowanceMethodology	2
CY2019	cbu	Number Of Calculations Used For General Loan Loss Allocation NumberOfCalculationsUsedForGeneralLoanLossAllocation	2
CY2019	cbu	Number Of Main Loan Segments NumberOfMainLoanSegments	5
CY2019	cbu	Period Of Historical Net Charge Off Data For Each Loan Class Used In Determining Allowance Level PeriodOfHistoricalNetChargeOffDataForEachLoanClassUsedInDeterminingAllowanceLevel	P36M
CY2019	cbu	Number Of Qualitative Environmental Factors Used In Qualitative Calculation For Loan Loss Allocation NumberOfQualitativeEnvironmentalFactorsUsedInQualitativeCalculationForLoanLossAllocation	8
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions	88
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	710602000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	8351000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions	169
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	576527000
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
CY2019	us-gaap	Advertising Expense AdvertisingExpense	7100000
CY2018	us-gaap	Advertising Expense AdvertisingExpense	5100000
CY2017	us-gaap	Advertising Expense AdvertisingExpense	5700000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	62
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	83378000
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	789000
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	150
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	793980000
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	9140000
CY2019	us-gaap	Prior Period Reclassification Adjustment Description PriorPeriodReclassificationAdjustmentDescription	<span style="color: #000000; font-family: 'Times New Roman'; font-size: 10pt; font-style: italic; font-weight: bold;">Reclassifications</span> <div style="text-align: left; color: #000000; font-family: 'Times New Roman'; font-size: 10pt;">Certain reclassifications have been made to prior years’ balances to conform to the current year presentation.</div>
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 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	3259000
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Short Term Advances BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedShortTermAdvances	-0
CY2019Q3	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Securities Sold Under Agreement To Repurchase Short Term BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSecuritiesSoldUnderAgreementToRepurchaseShortTerm	-0
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
CY2019Q4	cbu	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities Subordinated Notes Payable BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesSubordinatedNotesPayable	-0
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	54727000
CY2019Q3	us-gaap	Goodwill Goodwill	40307000
CY2019	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	8600000
CY2018	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	-800000
CY2017	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	26000000.0
CY2019	cbu	Business Acquisitions Pro Forma Acquisition Related Expenses BusinessAcquisitionsProFormaAcquisitionRelatedExpenses	8000000.0
CY2017	cbu	Business Acquisitions Pro Forma Acquisition Related Expenses BusinessAcquisitionsProFormaAcquisitionRelatedExpenses	25700000
CY2019	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	602817000
CY2018	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	594174000
CY2017	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	546977000
CY2016	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	536183000
CY2019	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	178427000
CY2018	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	167914000
CY2017	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	176257000
CY2016	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	109186000
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
CY2018Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	2952278000
CY2018Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	10339000
CY2018Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	26568000
CY2018Q4	us-gaap	Available For Sale Securities AvailableForSaleSecurities	2936049000
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
CY2018Q4	us-gaap	Equity Securities Fv Ni Cost EquitySecuritiesFvNiCost	251000
CY2018Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Gain Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedGainBeforeTax	200000
CY2018Q4	cbu	Equity Securities Fv Ni Accumulated Gross Unrealized Loss Before Tax EquitySecuritiesFvNiAccumulatedGrossUnrealizedLossBeforeTax	19000
CY2018Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	432000
CY2019Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	42965000
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
CY2018Q4	cbu	Other Investments And Equity Securities At Cost OtherInvestmentsAndEquitySecuritiesAtCost	44678000
CY2018Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Gain Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedGainBeforeTax	950000
CY2018Q4	cbu	Other Investments And Equity Securities Accumulated Gross Unrealized Loss Before Tax OtherInvestmentsAndEquitySecuritiesAccumulatedGrossUnrealizedLossBeforeTax	19000
CY2018Q4	cbu	Other Investment And Equity Securities Fair Value OtherInvestmentAndEquitySecuritiesFairValue	45609000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	1156000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	384
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	1584618000
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	25412000
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	553
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	2161145000
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	26568000
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position Less Than12 Months Number Of Positions EquityAndOtherSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsNumberOfPositions	1
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position Less Than12 Months EquityAndOtherSecuritiesContinuousUnrealizedLossPositionLessThan12Months	82000
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss EquityAndOtherSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	19000
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position12 Months Or Longer Number Of Positions EquityAndOtherSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerNumberOfPositions	0
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position12 Months Or Longer EquityAndOtherSecuritiesContinuousUnrealizedLossPosition12MonthsOrLonger	0
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss EquityAndOtherSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	0
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position Number Of Positions EquityAndOtherSecuritiesContinuousUnrealizedLossPositionNumberOfPositions	1
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position EquityAndOtherSecuritiesContinuousUnrealizedLossPosition	82000
CY2018Q4	cbu	Equity And Other Securities Continuous Unrealized Loss Position Accumulated Loss EquityAndOtherSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss	19000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingBalance	7400000
CY2018Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	437000
CY2017Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	976000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost	677169000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	680805000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	905531000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	925987000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	453320000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	456833000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	494419000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	494870000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date Amortized Cost Basis AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis	2530439000
CY2019Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate	2558495000
CY2019Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	3011551000
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	3044428000
CY2019Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	1471000000
CY2018Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	1447000000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Outstanding Principal Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingPrincipalBalance	16200000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Outstanding Principal Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingPrincipalBalance	6936000
CY2019Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	6890543000
CY2018Q4	us-gaap	Loans And Leases Receivable Gross Carrying Amount LoansAndLeasesReceivableGrossCarryingAmount	6281121000
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49911000
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	49284000
CY2019Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	6840632000
CY2018Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	6231837000
CY2019Q4	us-gaap	Unamortized Loan Commitment And Origination Fees And Unamortized Discounts Or Premiums UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums	32300000
CY2018Q4	us-gaap	Unamortized Loan Commitment And Origination Fees And Unamortized Discounts Or Premiums UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums	28400000
CY2019	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Additions CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions	551000
CY2018	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Additions CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions	0
CY2019	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	493000
CY2018	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	783000
CY2018Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	20661000
CY2017Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	22344000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	5720000
CY2018	us-gaap	Loans And Leases Receivable Related Parties Additions LoansAndLeasesReceivableRelatedPartiesAdditions	2600000
CY2019	us-gaap	Loans And Leases Receivable Related Parties Proceeds LoansAndLeasesReceivableRelatedPartiesProceeds	8895000
CY2018	us-gaap	Loans And Leases Receivable Related Parties Proceeds LoansAndLeasesReceivableRelatedPartiesProceeds	4283000
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	17486000
CY2018Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	20661000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentCarryingAmountNet	11797000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentCarryingAmountNet	5446000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Non Impairment Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairmentOutstandingBalance	1448046000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Non Impairment Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairmentOutstandingBalance	1271584000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Non Impaired Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairedCarryingAmountNet	1428154000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Non Impaired Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesNonImpairedCarryingAmountNet	1247691000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impaired And Non Impaired Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedOutstandingBalance	1464246000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impaired And Non Impaired Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedOutstandingBalance	1278520000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impaired And Non Impaired Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedCarryingAmountNet	1439951000
CY2018Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impaired And Non Impaired Carrying Amount Net CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairedAndNonImpairedCarryingAmountNet	1253137000
CY2019Q4	cbu	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Impairment Outstanding Balance CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesImpairmentOutstandingBalance	17100000
CY2019	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	138000
CY2018	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	244000
CY2019Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	633000
CY2018Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	437000
CY2019Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	0
CY2018Q4	us-gaap	Impaired Financing Receivable With No Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance	3956000
CY2019Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	1414000
CY2018Q4	us-gaap	Impaired Financing Receivable With Related Allowance Unpaid Principal Balance ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance	2230000
CY2019Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	1414000
CY2018Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	6186000
CY2019Q4	cbu	Impaired Financing Receivable Contractual Balance ImpairedFinancingReceivableContractualBalance	2944000
CY2018Q4	cbu	Impaired Financing Receivable Contractual Balance ImpairedFinancingReceivableContractualBalance	12078000
CY2019Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	0
CY2018Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	956000
CY2019	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	5078000
CY2018	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	7618000
CY2019	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod	0
CY2018	us-gaap	Impaired Financing Receivable Interest Income Accrual Method ImpairedFinancingReceivableInterestIncomeAccrualMethod	0
CY2019Q4	cbu	Financing Receivable Modifications Number Of Contracts FinancingReceivableModificationsNumberOfContracts	248
CY2019Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	6982000
CY2018Q4	cbu	Financing Receivable Modifications Number Of Contracts FinancingReceivableModificationsNumberOfContracts	218
CY2018Q4	us-gaap	Financing Receivable Modifications Recorded Investment FinancingReceivableModificationsRecordedInvestment	5525000
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	73
CY2019	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	2798000
CY2018	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	52
CY2018	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	1035000
CY2016Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	47233000
CY2017	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	16757000
CY2017	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	6123000
CY2017	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10984000
CY2017Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	47583000
CY2018	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	15486000
CY2018	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	6350000
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10837000
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
CY2019	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Provisions ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisions	326000
CY2018	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Provisions ValuationAllowanceForImpairmentOfRecognizedServicingAssetsProvisions	-0
CY2019	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Recoveries ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRecoveries	28000
CY2018	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Recoveries ValuationAllowanceForImpairmentOfRecognizedServicingAssetsRecoveries	0
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
CY2019Q4	cbu	Servicing Asset At Amortized Cost Net ServicingAssetAtAmortizedCostNet	674000
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	297920000
CY2018Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	247549000
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	133282000
CY2018Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	127561000
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	164638000
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	119988000
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
CY2018Q4	us-gaap	Finite Lived Intangible Assets Gross FiniteLivedIntangibleAssetsGross	150518000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	76672000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	73846000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	13800000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	11786000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	10105000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	8457000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	7041000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	11924000
CY2019Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	63113000
CY2018Q4	cbu	Servicing Asset At Amortized Cost Net ServicingAssetAtAmortizedCostNet	1137000
CY2019Q4	us-gaap	Servicing Asset At Amortized Value Fair Value ServicingAssetAtAmortizedValueFairValue	1362000
CY2017Q4	us-gaap	Goodwill Gross GoodwillGross	739254000
CY2018	us-gaap	Goodwill Written Off Related To Sale Of Business Unit GoodwillWrittenOffRelatedToSaleOfBusinessUnit	927000
CY2018Q4	us-gaap	Goodwill Gross GoodwillGross	738327000
CY2019	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	40307000
CY2019Q4	us-gaap	Goodwill Gross GoodwillGross	778634000
CY2017Q4	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	4824000
CY2018	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	-0
CY2018Q4	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	4824000
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	-0
CY2019Q4	us-gaap	Goodwill Impaired Accumulated Impairment Loss GoodwillImpairedAccumulatedImpairmentLoss	4824000
CY2017Q4	us-gaap	Goodwill Goodwill	734430000
CY2018	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	-927000
CY2018Q4	us-gaap	Goodwill Goodwill	733503000
CY2019	us-gaap	Goodwill Period Increase Decrease GoodwillPeriodIncreaseDecrease	40307000
CY2019Q4	us-gaap	Goodwill Goodwill	773810000
CY2018	us-gaap	Interest Expense Deposits InterestExpenseDeposits	10658000
CY2017	us-gaap	Interest Expense Deposits InterestExpenseDeposits	8031000
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	7773000
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	9180000
CY2018Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	1137000
CY2017Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	1358000
CY2019	us-gaap	Servicing Asset At Amortized Value Additions ServicingAssetAtAmortizedValueAdditions	17000
CY2018	us-gaap	Servicing Asset At Amortized Value Additions ServicingAssetAtAmortizedValueAdditions	228000
CY2019	cbu	Servicing Asset At Amortized Cost Increase Due To Business Acquisition ServicingAssetAtAmortizedCostIncreaseDueToBusinessAcquisition	196000
CY2018	cbu	Servicing Asset At Amortized Cost Increase Due To Business Acquisition ServicingAssetAtAmortizedCostIncreaseDueToBusinessAcquisition	0
CY2019	us-gaap	Servicing Asset At Amortized Value Amortization1 ServicingAssetAtAmortizedValueAmortization1	378000
CY2018	us-gaap	Servicing Asset At Amortized Value Amortization1 ServicingAssetAtAmortizedValueAmortization1	449000
CY2019Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	972000
CY2018Q4	us-gaap	Servicing Asset At Amortized Value ServicingAssetAtAmortizedValue	1137000
CY2018Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	-0
CY2017Q4	us-gaap	Valuation Allowance For Impairment Of Recognized Servicing Assets Balance ValuationAllowanceForImpairmentOfRecognizedServicingAssetsBalance	-0
CY2018Q4	us-gaap	Servicing Asset At Amortized Value Fair Value ServicingAssetAtAmortizedValueFairValue	2397000
CY2019	us-gaap	Mortgage Loans On Real Estate Cost Of Mortgages Sold MortgageLoansOnRealEstateCostOfMortgagesSold	2204000
CY2018	us-gaap	Mortgage Loans On Real Estate Cost Of Mortgages Sold MortgageLoansOnRealEstateCostOfMortgagesSold	18228000
CY2019Q4	cbu	Mortgage Loans Serviced For Others MortgageLoansServicedForOthers	294093000
CY2018Q4	cbu	Mortgage Loans Serviced For Others MortgageLoansServicedForOthers	333862000
CY2019Q4	cbu	Custodial Escrow Balances Maintained In Connection With Loans Serviced For Others CustodialEscrowBalancesMaintainedInConnectionWithLoansServicedForOthers	4596000
CY2018Q4	cbu	Custodial Escrow Balances Maintained In Connection With Loans Serviced For Others CustodialEscrowBalancesMaintainedInConnectionWithLoansServicedForOthers	4982000
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Weighted Average Life1 ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1	P20Y10M24D
CY2018	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Weighted Average Life1 ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1	P21Y4M24D
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed	0.187
CY2018	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed	0.093
CY2019	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Discount Rate ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate	0.030
CY2018	us-gaap	Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Discount Rate ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate	0.036
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	34804000
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	32504000
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	31152000
CY2019Q4	us-gaap	Noninterest Bearing Domestic Deposit Checking NoninterestBearingDomesticDepositChecking	2465902000
CY2018Q4	us-gaap	Noninterest Bearing Domestic Deposit Checking NoninterestBearingDomesticDepositChecking	2312816000
CY2019Q4	us-gaap	Interest Bearing Domestic Deposit Checking InterestBearingDomesticDepositChecking	2138348000
CY2018Q4	us-gaap	Interest Bearing Domestic Deposit Checking InterestBearingDomesticDepositChecking	1920545000
CY2019Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1538203000
CY2018Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1448208000
CY2019Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	1916385000
CY2018Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	1901262000
CY2019Q4	us-gaap	Time Deposits TimeDeposits	936129000
CY2018Q4	us-gaap	Time Deposits TimeDeposits	739540000
CY2019Q4	us-gaap	Deposits Deposits	8994967000
CY2018Q4	us-gaap	Deposits Deposits	8322371000
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
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.007
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.192
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.208
CY2017	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.058
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	3678000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	1796000
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Checking InterestExpenseDomesticDepositLiabilitiesChecking	1032000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	942000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	858000
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	841000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	5836000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	3638000
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Money Market InterestExpenseDomesticDepositLiabilitiesMoneyMarket	2981000
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	10004000
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	4366000
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Time Deposit InterestExpenseDomesticDepositLiabilitiesTimeDeposit	3177000
CY2019	us-gaap	Interest Expense Deposits InterestExpenseDeposits	20460000
CY2019Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	505008000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More Next Twelve Months TimeDepositsMaturities250000OrMoreNextTwelveMonths	73893000
CY2019Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	162729000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More Year Two TimeDepositsMaturities250000OrMoreYearTwo	23356000
CY2019Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	84028000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More Year Three TimeDepositsMaturities250000OrMoreYearThree	7297000
CY2019Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	87907000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More Year Four TimeDepositsMaturities250000OrMoreYearFour	5719000
CY2019Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	96439000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More Year Five TimeDepositsMaturities250000OrMoreYearFive	20252000
CY2019Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	18000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More After Year Five TimeDepositsMaturities250000OrMoreAfterYearFive	0
CY2019Q4	us-gaap	Time Deposits TimeDeposits	936129000
CY2019Q4	cbu	Time Deposits Maturities250000 Or More TimeDepositsMaturities250000OrMore	130517000
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.23
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	4000000
CY2011Q2	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Additional Shares Authorized ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized	900000
CY2019Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	8300000
CY2018Q4	cbu	Federal Home Loan Bank Overnight Advance FederalHomeLoanBankOvernightAdvance	54400000
CY2019Q4	us-gaap	Debt Instrument Unamortized Discount Premium Net DebtInstrumentUnamortizedDiscountPremiumNet	-795000
CY2018Q4	us-gaap	Debt Instrument Unamortized Discount Premium Net DebtInstrumentUnamortizedDiscountPremiumNet	0
CY2019Q4	us-gaap	Junior Subordinated Notes JuniorSubordinatedNotes	13795000
CY2018Q4	us-gaap	Junior Subordinated Notes JuniorSubordinatedNotes	0
CY2019Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	77320000
CY2018Q4	us-gaap	Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust JuniorSubordinatedDebentureOwedToUnconsolidatedSubsidiaryTrust	97939000
CY2019Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	241708000
CY2018Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	259367000
CY2019Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	3750000
CY2018Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	1976000
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	344873000
CY2018Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	413682000
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations Including Current Maturities LongTermDebtAndCapitalLeaseObligationsIncludingCurrentMaturities	344873000
CY2019Q4	us-gaap	Debt Weighted Average Interest Rate DebtWeightedAverageInterestRate	0.0165
CY2019	us-gaap	Long Term Debt Weighted Average Interest Rate Over Time LongTermDebtWeightedAverageInterestRateOverTime	0.0186
CY2018	us-gaap	Long Term Debt Weighted Average Interest Rate Over Time LongTermDebtWeightedAverageInterestRateOverTime	0.0172
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2019Q4	cbu	Number Of Unconsolidated Subsidiary Business Trusts Owned NumberOfUnconsolidatedSubsidiaryBusinessTrustsOwned	1
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	6788000
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-699000
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	2122000
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-28146000
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
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-546000
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	40275000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	44347000
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9248000
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.015
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.016
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Tax Exempt Income EffectiveIncomeTaxRateReconciliationTaxExemptIncome	0.038
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
CY2017	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.025
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
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
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant	1200000
CY2018	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	0
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	12059000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	12131000
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	5393000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeBenefits	4479000
CY2019Q4	cbu	Deferred Tax Assets Tax Deferred Expense Operating Lease Liabilities DeferredTaxAssetsTaxDeferredExpenseOperatingLeaseLiabilities	9801000
CY2018Q4	cbu	Deferred Tax Assets Tax Deferred Expense Operating Lease Liabilities DeferredTaxAssetsTaxDeferredExpenseOperatingLeaseLiabilities	0
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	837000
CY2018Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	541000
CY2019Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	28090000
CY2018Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	17151000
CY2019Q4	cbu	Deferred Tax Liabilities Unrealized Gains On Investment Securities DeferredTaxLiabilitiesUnrealizedGainsOnInvestmentSecurities	21547000
CY2018Q4	cbu	Deferred Tax Liabilities Unrealized Gains On Investment Securities DeferredTaxLiabilitiesUnrealizedGainsOnInvestmentSecurities	14451000
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Goodwill DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill	39189000
CY2018Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Goodwill DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill	39540000
CY2019Q4	cbu	Deferred Tax Liabilities Right Of Use Assets DeferredTaxLiabilitiesRightOfUseAssets	9566000
CY2018Q4	cbu	Deferred Tax Liabilities Right Of Use Assets DeferredTaxLiabilitiesRightOfUseAssets	0
CY2019Q4	cbu	Deferred Tax Liabilities Deferred Expense Deferred Loan Origination Costs DeferredTaxLiabilitiesDeferredExpenseDeferredLoanOriginationCosts	7639000
CY2018Q4	cbu	Deferred Tax Liabilities Deferred Expense Deferred Loan Origination Costs DeferredTaxLiabilitiesDeferredExpenseDeferredLoanOriginationCosts	6851000
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	2736000
CY2018Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	3098000
CY2019Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	162000
CY2018Q4	us-gaap	Deferred Tax Liabilities Mortgage Servicing Rights DeferredTaxLiabilitiesMortgageServicingRights	277000
CY2019Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	13769000
CY2018Q4	us-gaap	Deferred Tax Liabilities Prepaid Expenses DeferredTaxLiabilitiesPrepaidExpenses	11078000
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	94608000
CY2018Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	75295000
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	66518000
CY2018Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	58144000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.020
CY2019	cbu	Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of2017 Deferred Tax Asset Income Tax Expense Percentage EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActOf2017DeferredTaxAssetIncomeTaxExpensePercentage	0
CY2018	cbu	Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of2017 Deferred Tax Asset Income Tax Expense Percentage EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActOf2017DeferredTaxAssetIncomeTaxExpensePercentage	0
CY2017	cbu	Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of2017 Deferred Tax Asset Income Tax Expense Percentage EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActOf2017DeferredTaxAssetIncomeTaxExpensePercentage	-0.237
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
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.015
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	24000
CY2016Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	92000
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
CY2017	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	68000
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	24000
CY2019Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	0
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.35
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2017	cbu	Marginal Income Tax Rate MarginalIncomeTaxRate	0.3770
CY2018	cbu	Marginal Income Tax Rate MarginalIncomeTaxRate	0.2429
CY2018	us-gaap	Tax Cuts And Jobs Act Of2017 Change In Tax Rate Income Tax Expense Benefit TaxCutsAndJobsActOf2017ChangeInTaxRateIncomeTaxExpenseBenefit	-38000000.0
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P5Y11M4D
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P4Y9M7D
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	42300000
CY2019Q4	us-gaap	Statutory Accounting Practices Statutory Amount Available For Dividend Payments StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPayments	119300000
CY2019Q4	cbu	Bank Capital And Surplus Transferable To Company Maximum BankCapitalAndSurplusTransferableToCompanyMaximum	0.10
CY2019Q4	cbu	Aggregate Bank Capital And Surplus Transferable To Company Maximum AggregateBankCapitalAndSurplusTransferableToCompanyMaximum	0.20
CY2009	cbu	Other Comprehensive Income Loss Negative Postretirement Medical Plan Amendment Net Of Tax OtherComprehensiveIncomeLossNegativePostretirementMedicalPlanAmendmentNetOfTax	3500000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.0231
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.24
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.03
CY2019	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.58
CY2018Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.06375
CY2019	cbu	Maximum Percentage Of Pension Gain Loss Not Amortized MaximumPercentageOfPensionGainLossNotAmortized	0.10
CY2019Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	31800000
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsMethodUsed	Black-Scholes option-pricing model
CY2018	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	167897000
CY2017	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	150120000
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51732000
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51165000
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	48843000
CY2019Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Outstanding Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions	1502994
CY2019Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Exercise Price Beginning Balance1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1	42.82
CY2019	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Remaining Contractual Term2 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2	P5Y11M4D
CY2019Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Exercisable Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions	929120
CY2019Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Exercise Price1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1	36.73
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
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	12.78
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
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y6M
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
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.0319
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
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.2971
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
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
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	200000
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
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
CY2017	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-597000
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	168663000
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.26
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.28
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.07
CY2019	us-gaap	Net Income Loss NetIncomeLoss	169063000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	168641000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	150717000
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
CY2017	us-gaap	Amount Of Dilutive Securities Stock Options And Restrictive Stock Units AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits	-597000
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
CY2017	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	150120000
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51732000
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	51165000
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	48843000
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
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	627000
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	52248000
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	51748000
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	49470000
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.44
CY2017	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.32
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CY2018Q4	us-gaap	Stock Repurchase Program Number Of Shares Authorized To Be Repurchased StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased	2600000
CY2019	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	0
CY2019Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Face Amount Liability FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability	1181652000
CY2018Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Face Amount Liability FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability	1167745000
CY2019Q4	us-gaap	Line Of Credit Facility Current Borrowing Capacity LineOfCreditFacilityCurrentBorrowingCapacity	25000000.0
CY2019Q4	us-gaap	Federal Home Loan Bank Advances General Debt Obligations Disclosures Amount Of Available Unused Funds FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds	1800000000
CY2019Q4	cbu	Federal Reserve Advances General Debt Obligations Disclosures Amount Of Available Unused Funds FederalReserveAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds	25100000
CY2019Q4	cbu	Federal Reserve Required Average Total Reserve FederalReserveRequiredAverageTotalReserve	100300000
CY2019Q4	cbu	Federal Reserve Required Cash Deposit FederalReserveRequiredCashDeposit	77200000
CY2019Q4	cbu	Federal Reserve Required Reserve Deposit FederalReserveRequiredReserveDeposit	23100000
CY2019	cbu	Lessee Operating Lease Option To Terminate Term LesseeOperatingLeaseOptionToTerminateTerm	P1Y
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	11150000
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	8724000
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	18000
CY2019	us-gaap	Short Term Lease Cost ShortTermLeaseCost	240000
CY2019	us-gaap	Lease Cost LeaseCost	8982000
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	7938000
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	14145000
CY2019Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.070
CY2019Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.085
CY2018Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.07875
CY2018Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.09875
CY2019Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	1148336000
CY2019Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	0.1080
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	39895000
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	40913000
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P6Y7M6D
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0295
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 LesseeOperatingLeaseLiabilityPaymentsDue	45422000
CY2019Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	4509000
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	40913000
CY2019Q4	us-gaap	Lessee Operating Lease Lease Not Yet Commenced Term Of Contract1 LesseeOperatingLeaseLeaseNotYetCommencedTermOfContract1	P5Y
CY2019Q4	cbu	Operating Lease Lease Not Yet Commenced Liability OperatingLeaseLeaseNotYetCommencedLiability	600000
CY2019Q4	cbu	Operating Lease Lease Not Yet Commenced Right Of Use Asset OperatingLeaseLeaseNotYetCommencedRightOfUseAsset	600000
CY2018	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	9000000.0
CY2017	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	7300000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due Current OperatingLeasesFutureMinimumPaymentsDueCurrent	8452000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due In Two Years OperatingLeasesFutureMinimumPaymentsDueInTwoYears	7262000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due In Three Years OperatingLeasesFutureMinimumPaymentsDueInThreeYears	5673000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due In Four Years OperatingLeasesFutureMinimumPaymentsDueInFourYears	4411000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due In Five Years OperatingLeasesFutureMinimumPaymentsDueInFiveYears	2621000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due Thereafter OperatingLeasesFutureMinimumPaymentsDueThereafter	10390000
CY2018Q4	us-gaap	Operating Leases Future Minimum Payments Due OperatingLeasesFutureMinimumPaymentsDue	38809000
CY2019Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.105
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	0.0400
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	0.0500
CY2019Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	1148336000
CY2019Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	0.1723
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	0.0600
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	0.0800
CY2019Q4	us-gaap	Capital Capital	1198724000
CY2019Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	0.1799
CY2019Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	533112000
CY2019Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0800
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	0.1000
CY2019Q4	us-gaap	Common Equity Tier One Capital CommonEquityTierOneCapital	1073281000
CY2019Q4	us-gaap	Common Equity Tier One Capital Ratio CommonEquityTierOneCapitalRatio	0.1611
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
CY2018Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	1093166000
CY2018Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	0.1108
CY2018Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy TierOneLeverageCapitalRequiredForCapitalAdequacy	394700000
CY2018Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.0400
CY2018Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized TierOneLeverageCapitalRequiredToBeWellCapitalized	493375000
CY2018Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	0.0500
CY2018Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	1093166000
CY2018Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	0.1823
CY2018Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy TierOneRiskBasedCapitalRequiredForCapitalAdequacy	359747000
CY2018Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0600
CY2018Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	472168000
CY2018Q4	cbu	Tier One Risk Based Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.07875
CY2018Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized TierOneRiskBasedCapitalRequiredToBeWellCapitalized	479662000
CY2018Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.0800
CY2018Q4	us-gaap	Capital Capital	1142927000
CY2018Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	0.1906
CY2018Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	479662000
CY2018Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0800
CY2018Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer CapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	592083000
CY2018Q4	cbu	Capital Required For Capital Adequacy Plus Capital Conservation Buffer To Risk Weighted Assets CapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferToRiskWeightedAssets	0.09875
CY2018Q4	us-gaap	Capital Required To Be Well Capitalized CapitalRequiredToBeWellCapitalized	599578000
CY2018Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.1000
CY2018Q4	us-gaap	Common Equity Tier One Capital CommonEquityTierOneCapital	998111000
CY2018Q4	us-gaap	Common Equity Tier One Capital Ratio CommonEquityTierOneCapitalRatio	0.1665
CY2018Q4	us-gaap	Common Equity Tier One Capital Required For Capital Adequacy CommonEquityTierOneCapitalRequiredForCapitalAdequacy	269810000
CY2018Q4	cbu	Common Equity Tier1 Capital Required For Capital Adequacy Ratio CommonEquityTier1CapitalRequiredForCapitalAdequacyRatio	0.0450
CY2018Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBuffer	382231000
CY2018Q4	cbu	Common Equity Tier One Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio CommonEquityTierOneCapitalRequiredForCapitalAdequacyPlusCapitalConservationBufferRatio	0.06375
CY2018Q4	us-gaap	Common Equity Tier One Capital Required To Be Well Capitalized CommonEquityTierOneCapitalRequiredToBeWellCapitalized	389726000
CY2018Q4	cbu	Common Equity Tier1 Capital Required To Be Well Capitalized Ratio CommonEquityTier1CapitalRequiredToBeWellCapitalizedRatio	0.0650
CY2017	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	16941000
CY2017	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	25986000
CY2017	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	304222000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	159965000
CY2017Q4	us-gaap	Assets Assets	10746198000
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	851000
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	586000
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
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
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
CY2017	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	315675000
CY2017	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	10984000
CY2017	us-gaap	Noninterest Income NoninterestIncome	202423000
CY2017Q4	us-gaap	Goodwill Goodwill	734430000
CY2017Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	90658000

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$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

2018 Q4 Form 10-K Financial Statement

#000114036120004510 Filed on March 02, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$CBU COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu

2018 Q4 Form 10-K Financial Statement

#000114036120004510 Filed on March 02, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$CBU
COMMUNITY FINANCIAL SYSTEM, INC. Stock $cbu