v3.26.1
STATEMENTS OF NET ASSETS AVAILABLE FOR PLAN BENEFITS - NBT Bancorp Inc. 401(k) and Employee Stock Ownership Plan [Member] - USD ($)
Dec. 31, 2025
Dec. 31, 2024
Investments, at fair value:    
Investments, at fair value $ 411,209,167 $ 360,983,991
Receivables:    
Notes receivable from participants 3,492,310 3,450,393
Due from broker 86,234 62,387
Contributions receivable from employer 675,053 1,987,973
Total receivables 4,253,597 5,500,753
Total assets 415,462,764 366,484,744
Liabilities    
Due to broker 92,118 41,865
Total liabilities 92,118 41,865
Net assets available for plan benefits 415,370,646 366,442,879
Mutual Funds [Member]    
Investments, at fair value:    
Investments, at fair value 363,169,532 307,131,380
Common Stock of NBT Bancorp Inc. [Member]    
Investments, at fair value:    
Investments, at fair value 30,074,182 35,226,305
Stable Value Fund [Member]    
Investments, at fair value:    
Investments, at fair value 17,933,465 18,539,578
Cash and Money Market Funds [Member]    
Investments, at fair value:    
Investments, at fair value $ 31,988 $ 86,728