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v3.23.1

Allowance for Credit Losses and Credit Quality of Loans, Amortized Cost Basis of Loans Modified to Borrowers Experiencing Financial Difficulty (Details) - Term Extension [Member] $ in Thousands | 3 Months Ended
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Mar. 31, 2023 USD ($)
Modified Loans Disaggregated by Class of Financing Receivable and Type of Concession Granted [Abstract] |
Amortized cost | $ 43
% of total class of financing receivables | 0.002%
Residential [Member] |
Modified Loans Disaggregated by Class of Financing Receivable and Type of Concession Granted [Abstract] |
Amortized cost | $ 43
% of total class of financing receivables | 0.002%

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- Definition Amortized cost of financing receivable modified during period for debtor experiencing financial difficulty. + References No definition available. + Details
Name: | nbtb_FinancingReceivableModifiedInPeriodAmount
Namespace Prefix: | nbtb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Percentage of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables. + References No definition available. + Details
Name: | nbtb_FinancingReceivableModifiedInPeriodToTotalFinancingReceivablesPercentage
Namespace Prefix: | nbtb_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | nbtb_FinancingReceivableModifiedLoansDisaggregatedByClassOfFinancingReceivableAndTypeOfConcessionGrantedAbstract
Namespace Prefix: | nbtb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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