XML 26 R32.htm IDEA: XBRL DOCUMENT v2.4.1.9
Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]      
Balance as of Beginning of Period $ 66,359,000us-gaap_FinancingReceivableAllowanceForCreditLosses $ 69,434,000us-gaap_FinancingReceivableAllowanceForCreditLosses  
Charge-offs (5,680,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs (4,830,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs  
Recoveries 1,038,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery 1,234,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery  
Provision 3,642,000us-gaap_ProvisionForLoanLeaseAndOtherLosses 3,596,000us-gaap_ProvisionForLoanLeaseAndOtherLosses  
Balance as of Ending of Period 65,359,000us-gaap_FinancingReceivableAllowanceForCreditLosses 69,434,000us-gaap_FinancingReceivableAllowanceForCreditLosses  
Allowance for loan losses for acquired loan portfolio 1.9us-gaap_AllowanceForLoanAndLeaseLossesLoansAcquired 0us-gaap_AllowanceForLoanAndLeaseLossesLoansAcquired  
Provision expense and net charge-offs related to acquired loans 600,000nbtb_AllowanceForLoanAndLeaseLossesLoansAcquiredProvisionAndChargeOffs 200,000nbtb_AllowanceForLoanAndLeaseLossesLoansAcquiredProvisionAndChargeOffs  
Allowance loan losses [Abstract]      
Allowance for loan losses 65,359,000us-gaap_FinancingReceivableAllowanceForCreditLosses 69,434,000us-gaap_FinancingReceivableAllowanceForCreditLosses  
Allowance for loans individually evaluated for impairment 2,950,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1   1,100,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Allowance for loans collectively evaluated for impairment 62,409,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment   65,259,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Ending balance of loans 5,623,023,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome   5,595,271,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Commercial Loans [Member]      
Financing Receivable, Allowance for Credit Losses [Roll Forward]      
Balance as of Beginning of Period 32,433,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
35,090,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Charge-offs (798,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
(479,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Recoveries 234,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
399,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Provision (591,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
(573,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Balance as of Ending of Period 31,278,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
34,437,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Allowance loan losses [Abstract]      
Allowance for loan losses 31,278,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
34,437,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
 
Allowance for loans individually evaluated for impairment 2,950,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  1,100,000us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Allowance for loans collectively evaluated for impairment 28,328,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  31,333,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Ending balance of loans 2,484,300,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  2,473,702,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Consumer Loans [Member]      
Financing Receivable, Allowance for Credit Losses [Roll Forward]      
Balance as of Beginning of Period 26,720,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
27,694,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Charge-offs (4,378,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
(4,032,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Recoveries 748,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
741,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Provision 3,066,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
4,033,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Balance as of Ending of Period 26,156,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
28,436,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Allowance loan losses [Abstract]      
Allowance for loan losses 26,156,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
28,436,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
 
Allowance for loans individually evaluated for impairment 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Allowance for loans collectively evaluated for impairment 26,156,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  26,720,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance of loans 2,013,123,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  2,005,980,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Residential Real Estate Mortgages [Member]      
Financing Receivable, Allowance for Credit Losses [Roll Forward]      
Balance as of Beginning of Period 7,130,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
6,520,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Charge-offs (504,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
(319,000)us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Recoveries 56,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
94,000us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Provision 1,016,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
(70,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Balance as of Ending of Period 7,698,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
6,225,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Allowance loan losses [Abstract]      
Allowance for loan losses 7,698,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
6,225,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
 
Allowance for loans individually evaluated for impairment 0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  0us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Allowance for loans collectively evaluated for impairment 7,698,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  7,130,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Ending balance of loans 1,125,600,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  1,115,589,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Unallocated [Member]      
Financing Receivable, Allowance for Credit Losses [Roll Forward]      
Balance as of Beginning of Period 76,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
130,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Charge-offs 0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
0us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Recoveries 0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
0us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Provision 151,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
206,000us-gaap_ProvisionForLoanLeaseAndOtherLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Balance as of Ending of Period 227,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
336,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Allowance loan losses [Abstract]      
Allowance for loan losses 227,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
336,000us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
 
Allowance for loans collectively evaluated for impairment 227,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
  76,000us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_UnallocatedFinancingReceivablesMember
Originated Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 4,904,253,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
  4,847,937,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
Ending balance of loans individually evaluated for impairment 22,945,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
  20,121,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
Ending balance of loans collectively evaluated for impairment 4,881,308,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
  4,827,816,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
Originated Loans [Member] | Commercial Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 2,159,062,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  2,140,371,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 12,253,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  11,079,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment 2,146,809,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  2,129,292,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Originated Loans [Member] | Consumer Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 1,880,448,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  1,858,724,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 6,423,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  5,498,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment 1,874,025,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  1,853,226,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Originated Loans [Member] | Residential Real Estate Mortgages [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 864,743,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  848,842,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 4,269,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  3,544,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment 860,474,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  845,298,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_OriginatedLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Acquired Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 718,770,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
  747,334,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
Ending balance of loans individually evaluated for impairment 9,772,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
  5,675,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
Ending balance of loans collectively evaluated for impairment 708,998,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
  741,659,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
Acquired Loans [Member] | Commercial Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 325,238,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  333,331,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 9,772,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  5,675,000us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment 315,466,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
  327,656,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialPortfolioSegmentMember
Acquired Loans [Member] | Consumer Loans [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 132,675,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  147,256,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment 132,675,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
  147,256,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerPortfolioSegmentMember
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]      
Allowance loan losses [Abstract]      
Ending balance of loans 260,857,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  266,747,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Ending balance of loans individually evaluated for impairment 0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  0us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
Ending balance of loans collectively evaluated for impairment $ 260,857,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember
  $ 266,747,000us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ nbtb_ClassOfFinancingReceivablesAxis
= nbtb_AcquiredLoansMember
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember