Allowance for Loan Losses and Credit Quality of Loans (Details) - Jun. 30, 2015 $ in Millions	USD ($) Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan portfolio segments	3
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	80.00%
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	75.00%
Business Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Business banking loans, maximum amount \| $	$ 0.5
Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of automobile financing to indirect relationships with dealers (in hundredths)	75.00%
Principal repayment term of loan, minimum	3 years
Principal repayment term of loan, maximum	6 years
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Home equity loan amount, percentage of equity in home, maximum (in hundredths)	85.00%
Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal repayment term of loan, minimum	1 year
Principal repayment term of loan, maximum	10 years
Residential Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	85.00%

Represents the maximum repayment term of the debt instrument.

No definition available.

Name:	nbtb_DebtInstrumentRepaymentTermMaximum
Namespace Prefix:	nbtb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum repayment term of the debt instrument.

+ References

No definition available.

+ Details

Name:	nbtb_DebtInstrumentRepaymentTermMinimum
Namespace Prefix:	nbtb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the maximum percentage of the equity in home , for the originated amounts of home equity loans.

+ References

No definition available.

+ Details

Name:	nbtb_HomeEquityLoanOriginationAmountPercentageOfEuityInHomeMaximum
Namespace Prefix:	nbtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the maximum percentage of the appraised value or purchase price of a property, for the originated amounts of real estate loans.

+ References

No definition available.

+ Details

Name:	nbtb_LoanOriginationAmountPercentageOfAppraisedValueOfPropertyOrPurchasePriceMaximum
Namespace Prefix:	nbtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the number of portfolio segments within the loan portfolio.

+ References

No definition available.

+ Details

Name:	nbtb_LoanPortfolioSegments
Namespace Prefix:	nbtb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of automobile financing to indirect relationships the Company maintains with dealers.

+ References

No definition available.

+ Details

Name:	nbtb_PercentageOfAutomobileFinancingToIndirectRelationshipsWithDealers
Namespace Prefix:	nbtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the maximum loan amount available for small business customers.

+ References

No definition available.

+ Details

Name:	nbtb_SmallBusinessLoansAmountMaximum
Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nbtb_AgriculturalRealEstateFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nbtb_SmallBusinessFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nbtb_IndirectFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=nbtb_DirectFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: