Name:	nbtb_AverageReserveBalancesWithFederalReserveBank
Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Name:	nbtb_FederalReserveBankRequirementAbstract
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Data Type:	xbrli:stringItemType
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Period Type:	duration

Describe the approximate period of the guarantee or each group of similar guarantees.

No definition available.

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

The dollar amount of principal for mortgage loans being serviced for others.

No definition available.

Name:	nbtb_LoansServicedByCompanyForUnrelatedThirdParties
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Specific period of time established required to maintain reserve balances with the Federal Reserve Bank expressed in days.

No definition available.

Name:	nbtb_MaintenancePeriodBasisFederalReserveBank
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Data Type:	xbrli:durationItemType
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The percentage of the Company's loans secured by real estate.

No definition available.

Name:	nbtb_PercentageOfCompanysLoansSecuredByRealEstate
Namespace Prefix:	nbtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
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Data Type:	xbrli:stringItemType
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Name:	us-gaap_GuaranteeObligationsLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Name:	us-gaap_ServicingAsset
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Data Type:	xbrli:monetaryItemType
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Name:	us-gaap_GuaranteeObligationsByNatureAxis=nbtb_CommitmentToExtendCreditsCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=nbtb_LoansSoldWithRecourseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_FinancialStandbyLetterOfCreditMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_LetterOfCreditMember
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Data Type:	na
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