Borrowings, Junior Subordinated Debt (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 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
Trust preferred debt owed to trust	$ 18,720
Final maturity date	Aug. 01, 2029
CNBF Capital Trust I [Member] | LIBOR [Member]
Junior Subordinated Debt [Abstract]
Variable rate basis	3-month LIBOR
Basis spread on variable rate	2.75%
NBT Statutory Trust I [Member]
Junior Subordinated Debt [Abstract]
Issuance date	Nov. 01, 2005
Trust preferred securities outstanding	$ 5,000
Trust preferred debt owed to trust	$ 5,155
Final maturity date	Dec. 01, 2035
NBT Statutory Trust I [Member] | LIBOR [Member]
Junior Subordinated Debt [Abstract]
Variable rate basis	3-month LIBOR
Basis spread on variable rate	1.40%
NBT Statutory Trust II [Member]
Junior Subordinated Debt [Abstract]
Issuance date	Feb. 01, 2006
Trust preferred securities outstanding	$ 50,000
Trust preferred debt owed to trust	$ 51,547
Final maturity date	Mar. 01, 2036
NBT Statutory Trust II [Member] | LIBOR [Member]
Junior Subordinated Debt [Abstract]
Variable rate basis	3-month LIBOR
Basis spread on variable rate	1.40%
Alliance Financial Capital Trust I [Member]
Junior Subordinated Debt [Abstract]
Issuance date	Dec. 01, 2003
Trust preferred securities outstanding	$ 10,000
Trust preferred debt owed to trust	$ 10,310
Final maturity date	Jan. 01, 2034
Alliance Financial Capital Trust I [Member] | LIBOR [Member]
Junior Subordinated Debt [Abstract]
Variable rate basis	3-month LIBOR
Basis spread on variable rate	2.85%
Alliance Financial Capital Trust II [Member]
Junior Subordinated Debt [Abstract]
Issuance date	Sep. 01, 2006
Trust preferred securities outstanding	$ 15,000
Trust preferred debt owed to trust	$ 15,464
Final maturity date	Sep. 01, 2036
Alliance Financial Capital Trust II [Member] | LIBOR [Member]
Junior Subordinated Debt [Abstract]
Variable rate basis	3-month LIBOR
Basis spread on variable rate	1.65%
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