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Summary of Significant Accounting Policies, Other Financial Instruments (Details) | 12 Months Ended
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Dec. 31, 2024
Other Financial Instruments [Abstract] |
Standby letters of credit expiration period | 1 year

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

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- Definition Represents expiration period of standby letters of credit, 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_StandbyLettersOfCreditExpirationPeriod
Namespace Prefix: | nbtb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration