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Junior Subordinated Debt (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 USD ($) Trust Period
Debt Instrument [Line Items] |
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] |
Debt Instrument [Line Items] |
Number of wholly owned Delaware statutory business trusts | 1
CNBF Capital Trust I [Member] | LIBOR [Member] |
Debt Instrument [Line Items] |
Issuance Date | Aug. 01, 1999
Trust Preferred Securities Outstanding | $ 18,000
Variable rate basis | 3-month LIBOR
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] | LIBOR [Member] |
Debt Instrument [Line Items] |
Issuance Date | Nov. 01, 2005
Trust Preferred Securities Outstanding | $ 5,000
Variable rate basis | 3-month LIBOR
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] | LIBOR [Member] |
Debt Instrument [Line Items] |
Issuance Date | Feb. 01, 2006
Trust Preferred Securities Outstanding | $ 50,000
Variable rate basis | 3-month LIBOR
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] | LIBOR [Member] |
Debt Instrument [Line Items] |
Issuance Date | Dec. 01, 2003
Trust Preferred Securities Outstanding | $ 10,000
Variable rate basis | 3-month LIBOR
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] | LIBOR [Member] |
Debt Instrument [Line Items] |
Issuance Date | Sep. 01, 2006
Trust Preferred Securities Outstanding | $ 15,000
Variable rate basis | 3-month LIBOR
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] |
Debt Instrument [Line Items] |
Number of wholly owned Delaware statutory business trusts | 2
Trusts [Member] |
Debt Instrument [Line Items] |
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] |
Debt Instrument [Line Items] |
Trust equity method investment | $ 1,000

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