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Allowance for Loan Losses and Credit Quality of Loans (Details) - Jun. 30, 2015 $ in Millions | USD ($) Segment
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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%

X
- Definition Represents the maximum repayment term of the debt instrument. + References No definition available. + Details
Name: | nbtb_DebtInstrumentRepaymentTermMaximum
Namespace Prefix: | nbtb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- 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

X
- 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

X
- 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

X
- 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

X
- 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

X
- 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

X
- 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

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

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

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

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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