Summary of Significant Accounting Policies, Loans (Details)	12 Months Ended
Dec. 31, 2023
Loans [Abstract]
Minimum number of days past due for loans to be considered nonperforming	90 days
Period of sustained repayment performance for nonperforming TDRs to be returned to performing status	6 months

Period of sustained repayment performance for nonperforming TDRs to be returned to performing status, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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