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Borrowings, Junior Subordinated Debt (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 USD ($) Trust Period
Junior Subordinated Debt [Abstract] |
Number of statutory business trusts included in the Trusts | Trust | 5
Minimum assets for bank holding companies to be subject to the same capital requirements as insured depository institutions | $ 500,000
CNBF Capital Trust I [Member] |
Junior Subordinated Debt [Abstract] |
Number of wholly owned Delaware statutory business trusts | Trust | 1
Issuance date | Aug. 01, 1999
Trust preferred securities outstanding | $ 18,000
Variable rate basis | 3-month Term SOFR + 0.26161% plus 2.75%
Term of variable rate basis | 3 months
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] | nbtb:TermSecuredOvernightFinancingRateSOFRRateMember
Credit spread adjustment | 0.26161%
Basis spread on variable rate | 2.75%
Trust preferred debt owed to trust | $ 18,720
Final maturity date | Aug. 01, 2029
NBT Statutory Trust I [Member] |
Junior Subordinated Debt [Abstract] |
Issuance date | Nov. 01, 2005
Trust preferred securities outstanding | $ 5,000
Variable rate basis | 3-month Term SOFR + 0.26161% plus 1.40%
Term of variable rate basis | 3 months
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] | nbtb:TermSecuredOvernightFinancingRateSOFRRateMember
Credit spread adjustment | 0.26161%
Basis spread on variable rate | 1.40%
Trust preferred debt owed to trust | $ 5,155
Final maturity date | Dec. 01, 2035
NBT Statutory Trust II [Member] |
Junior Subordinated Debt [Abstract] |
Issuance date | Feb. 01, 2006
Trust preferred securities outstanding | $ 50,000
Variable rate basis | 3-month Term SOFR + 0.26161% plus 1.40%
Term of variable rate basis | 3 months
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] | nbtb:TermSecuredOvernightFinancingRateSOFRRateMember
Credit spread adjustment | 0.26161%
Basis spread on variable rate | 1.40%
Trust preferred debt owed to trust | $ 51,547
Final maturity date | Mar. 01, 2036
Alliance Financial Capital Trust I [Member] |
Junior Subordinated Debt [Abstract] |
Issuance date | Dec. 01, 2003
Trust preferred securities outstanding | $ 10,000
Variable rate basis | 3-month Term SOFR + 0.26161% plus 2.85%
Term of variable rate basis | 3 months
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] | nbtb:TermSecuredOvernightFinancingRateSOFRRateMember
Credit spread adjustment | 0.26161%
Basis spread on variable rate | 2.85%
Trust preferred debt owed to trust | $ 10,310
Final maturity date | Jan. 01, 2034
Alliance Financial Capital Trust II [Member] |
Junior Subordinated Debt [Abstract] |
Issuance date | Sep. 01, 2006
Trust preferred securities outstanding | $ 15,000
Variable rate basis | 3-month Term SOFR + 0.26161% plus 1.65%
Term of variable rate basis | 3 months
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration] | nbtb:TermSecuredOvernightFinancingRateSOFRRateMember
Credit spread adjustment | 0.26161%
Basis spread on variable rate | 1.65%
Trust preferred debt owed to trust | $ 15,464
Final maturity date | Sep. 01, 2036
Alliance Financial Capital [Member] |
Junior Subordinated Debt [Abstract] |
Number of wholly owned Delaware statutory business trusts | Trust | 2
Trusts [Member] |
Junior Subordinated Debt [Abstract] |
Trust preferred securities outstanding | $ 98,000
Trust preferred debt owed to trust | 101,000
Trust equity method investment | $ 3,200
Debentures period semi-annual deferral periods | Period | 10
Trust preferred securities included in Tier I capital | $ 97,000
NBT Bancorp Inc [Member] |
Junior Subordinated Debt [Abstract] |
Trust equity method investment | $ 1,000

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