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

Represent participant early retirement minimum service period under employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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

The percentage of employee contributions that are immediately vested in an employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	nbtb_EmployeeBenefitPlanEmployeeContributionVestingPercentage
Namespace Prefix:	nbtb_
Data Type:	dtr:percentItemType
Balance Type:	na
Period Type:	duration

Amount of plan asset, in forfeited account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	nbtb_EmployeeBenefitPlanForfeitedFromAccount
Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The period over which a participant loan (note receivable from participant account) is required to be repaid under the terms of the plan.

No definition available.

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

The amount of spread, margin, or percentage points above or below a referenced variable interest rate used to determine the interest rate charged on participant notes receivable.

No definition available.

Name:	nbtb_EmployeeBenefitPlanNoteReceivableFromParticipantAccountSpreadOnVariableRate
Namespace Prefix:	nbtb_
Data Type:	dtr:percentItemType
Balance Type:	na
Period Type:	duration

Participant age limit to participate in the employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	nbtb_EmployeeBenefitPlanParticipantAgeLimitToParticipateInPlan
Namespace Prefix:	nbtb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The period of employment an employee is required to complete before becoming eligible to participate in the plan.

No definition available.

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

The number of hours of service a participant must complete in order to become eligible to participate in the plan.

No definition available.

Name:	nbtb_EmployeeBenefitPlanParticipantServiceCompletedToBeEligibleToParticipateInPlan
Namespace Prefix:	nbtb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Participant eligible to participate upon completing the schedules service in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	nbtb_EmployeeBenefitPlanParticipantServiceScheduledToCompleteToBeEligibleToParticipateInPlan
Namespace Prefix:	nbtb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the minimum period of service required for a plan participant to become fully vested in the employer contributions under employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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

The participant's vested balance without requiring the participant's consent or request. If the vested balance does not exceed this threshold amount, the plan must distribute the balance regardless of participant under employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	nbtb_EmployeeBenefitPlanParticipantsVestedAccountValue
Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the period of time over which an employee must remain employed before becoming fully vested in the employer's contributions or benefits under employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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

Amount of increase in net asset available for benefit from cash contribution from employer of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForEmployerContributionCash
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Indicates (true false) whether description of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) is published and made available.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionAvailable
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:booleanItemType
Balance Type:	na
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-SubTopic 205
-Topic 962
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionMatchingPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of participant compensation eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanEmployerContributionParticipantCompensationMatchedPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of plan asset, in forfeited nonvested account, no longer allocated to participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of decrease in forfeited nonvested account of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from employer contribution.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(5)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

Name:	us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Percentage of maximum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow to total participant account balance.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Amount of minimum account balance that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) can borrow.

Name:	us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMinimumBorrowingAmount
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Name:	us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate
Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Name:	dei_LegalEntityAxis=nbtb_EBP002Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_ParticipantsContributionEligibleFor100MatchingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_ParticipantsContributionFrom1To5EligibleFor50MatchingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_CompanyMatchingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_DiscretionaryContributionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_WorkerRetirementAccumulationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_ParticipantsContributionsAndNetInvestmentIncomeOfLossMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_SafeHarborEmployerMatchingContributionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_TerminationDueToDeathRetirementOrPermanentDisabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_LoansOtherThanLoansForPurchaseOfPrimaryResidenceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap-ebp_EmployeeBenefitPlanContributionParticipatingEmployerAxis=nbtb_LoansForPurchaseOfPrimaryResidenceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: