Document and Entity Information
Oct. 28, 2019
Cover [Abstract]  
Document Type 8-K
Amendment Flag false
Document Period End Date Oct. 28, 2019
Entity Registrant Name NBT BANCORP INC.
Entity Incorporation, State or Country Code DE
Entity File Number 000-14703
Entity Tax Identification Number 16-1268674
Entity Address, Address Line One 52 South Broad Street
Entity Address, City or Town Norwich
Entity Address, State or Province NY
Entity Address, Postal Zip Code 13815
City Area Code 607
Local Phone Number 337-2265
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Emerging Growth Company false
Entity Central Index Key 0000790359
Title of 12(b) Security Common Stock, par value $0.01 per share
Trading Symbol NBTB
Security Exchange Name NASDAQ