Trust Preferred Debentures (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Debt Instrument [Line Items]
Proceeds from issuance of junior subordinated deferrable interest debentures to wholly owned trusts	$ 75.4
Wholly owned Delaware statutory business trusts - variable interest entities	three wholly owned Delaware statutory business trusts
Fixed rate to convert to a floating rate (in years)	5 years
Deferral period of payments of interest, description	ten consecutive semi-annual periods with respect to each deferral period
Tier I risk based regulatory capital included from Trust preferred securities issued by subsidiary trusts	74
Minimum assets for bank holding companies to be subject to the same capital requirements as insured depository institutions	500
CNBF Capital Trust I VIE Entity Not Primary Beneficiary [Member] | CNBF Capital Trust I Debenture [Member]
Debt Instrument [Line Items]
Trust preferred debt owed to trust	18.7
Trust preferred securities outstanding	18
Issuance Date	1999-06-30
Interest Rate	three-month LIBOR plus 275 basis points
Final maturity date	2029-08-31
Common equity securities issued by Variable Interest Entity to NBT	0.7
CNBF Trust I securities owned by bank	1
NBT Statutory Trust I VIE Entity Not Primary Beneficiary [Member] | NBT Statutory Trust I Debenture [Member]
Debt Instrument [Line Items]
Trust preferred debt owed to trust	5.2
Trust preferred securities outstanding	5
Issuance Date	2005-11-30
Interest Rate	three-month LIBOR plus 140 basis points
Final maturity date	2035-12-01
Common equity securities issued by Variable Interest Entity to NBT	0.2
Original issuance fixed interest rate (in hundredths)	6.30%
NBT Statutory Trust II VIE Entity Not Primary Beneficiary [Member] | NBT Statutory Trust II Debenture [Member]
Debt Instrument [Line Items]
Trust preferred debt owed to trust	51.5
Trust preferred securities outstanding	50
Issuance Date	2006-02-28
Interest Rate	three-month LIBOR plus 140 basis points
Final maturity date	2036-03-15
Common equity securities issued by Variable Interest Entity to NBT	$ 1.5
Original issuance fixed interest rate (in hundredths)	6.195%