Federal Reserve Bank Requirement (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Federal Reserve Bank Requirement [Abstract]
Federal Reserve Bank maintenance period (in days)	14D
Average reserve at Federal Reserve Bank for maintenance period	$ 33.4

For banks and other depository institutions, the calculated average reserve balance outstanding for the a specific period as of the Balance Sheet date. Includes noninterest bearing balances with the Federal Reserve Banks.

No definition available.

Name:	nbtb_AverageReserveBalancesWithFederalReserveBank
Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant