RETIREMENT AND POSTRETIREMENT PLANS - Net periodic benefit (credit) cost for the Employee Retirement Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense	Other Noninterest Expense
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 175		$ 525
Interest cost	$ 310	330	$ 930	990
Expected return on assets	(680)	(687)	(2,040)	(2,062)
Net periodic credit	(370)	(182)	(1,110)	(547)
Retirement Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	210	222	630	667
Expected return on assets	(360)	(382)	(1,080)	(1,147)
Amortization of unrealized loss	203	147	608	442
Net periodic credit	53	$ (13)	158	$ (38)
Supplemental Employee Retirement Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Contributions to the BNB Bank Pension Plan or the Employee Retirement Plan	$ 0		$ 0