Number of available for sale debt securities sold during the period.

No definition available.

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- Definition

Number of issuers that issued debt securities whose debt ratings were downgraded during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of regional financial institutions that issued debt securities during the period.

+ References

No definition available.

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

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

- Definition

Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27357-111563

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- Details

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Subsequent Event (Details) $ in Thousands		1 Months Ended	3 Months Ended
Subsequent Event (Details) $ in Thousands	May 04, 2023 USD ($) DebtSecurities FinancialInstitution	Apr. 30, 2023 FinancialInstitution	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale [Abstract]
Pre-tax loss on sale of AFS securities			$ (5,000)	$ (0)
Aggregate amortized cost			1,707,940		$ 1,743,882
Estimated fair value			1,512,008		1,527,225
Corporate [Member]
Debt Securities, Available-for-Sale [Abstract]
Aggregate amortized cost			55,414		60,404
Estimated fair value			47,237		$ 54,240
Subordinated Debt Securities [Member]
Debt Securities, Available-for-Sale [Abstract]
Aggregate amortized cost			7,000
Estimated fair value			$ 4,800
Subsequent Event [Member] \| Subordinated Debt Securities [Member]
Debt Securities, Available-for-Sale [Abstract]
Number of subordinated debt securities sold \| DebtSecurities	2
Pre-tax loss on sale of AFS securities	$ 4,500
Number of regional financial institutions that issued debt securities \| FinancialInstitution	2
Number of issuers of debt securities whose debt ratings were downgraded \| FinancialInstitution		2