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Summary of Significant Accounting Policies, Securities (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 USD ($)
Securities [Abstract] |
Allowance for credit losses - HTM debt securities | $ 0

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- References No definition available. + Details
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Namespace Prefix: | nbtb_
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Balance Type: | na
Period Type: | duration

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- Definition Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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Balance Type: | debit
Period Type: | duration