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Allowance for Loan Losses and Credit Quality of Loans (Details) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) Segment | Dec. 31, 2016 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Loan portfolio segments | Segment | 3 |
Commercial Loans [Member] | Commercial Real Estate [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Loan amount, percentage of appraised value or purchase price of the property | 80.00% |
Commercial Loans [Member] | Agricultural Real Estate [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Loan amount, percentage of appraised value or purchase price of the property | 75.00% |
Commercial Loans [Member] | Business Banking [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Business banking loans, amount available | $ 750 |
Consumer Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Unsecured consumer loans originated through relationship with leading national technology-driven consumer lending company | $ 403,600 | $ 374,900
Consumer Loans [Member] | Indirect [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Percentage of automobile financing to indirect relationships with dealers | 70.00% |
Consumer Loans [Member] | Indirect [Member] | Minimum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Principal repayment term of loan | 3 years |
Consumer Loans [Member] | Indirect [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Principal repayment term of loan | 6 years |
Consumer Loans [Member] | Home Equity [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Home equity loan amount, percentage of equity in home | 85.00% |
Consumer Loans [Member] | Direct [Member] | Minimum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Principal repayment term of loan | 1 year |
Consumer Loans [Member] | Direct [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Principal repayment term of loan | 10 years |
Residential Real Estate Mortgages [Member] | Maximum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Loan amount, percentage of appraised value or purchase price of the property | 85.00% |

X
- Definition Represents the principal repayment term of the financing receivable, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | nbtb_FinancingReceivablePrincipalRepaymentTerm
Namespace Prefix: | nbtb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the percentage of the equity in home, for the originated amounts of home equity loans. + References No definition available. + Details
Name: | nbtb_HomeEquityLoanOriginationAmountPercentageOfEquityInHome
Namespace Prefix: | nbtb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the percentage of the appraised value or purchase price of a property for the originated amounts of loans. + References No definition available. + Details
Name: | nbtb_LoanOriginationAmountPercentageOfAppraisedValueOrPurchasePriceOfProperty
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 loan amount available for business banking customers. + References No definition available. + Details
Name: | nbtb_SmallBusinessLoansAmountAvailable
Namespace Prefix: | nbtb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of unsecured consumer loans originated through relationship with leading national technology-driven consumer lending company. + References No definition available. + Details
Name: | nbtb_UnsecuredConsumerLoansOriginatedThroughRelationshipWithLeadingNationalTechnologyDrivenConsumerLendingCompany
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_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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