RETIREMENT AND POSTRETIREMENT PLANS - Net periodic cost for the Employee Retirement Plan (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Net Periodic Benefit Cost
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	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
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
Settlement loss recognized	$ (7,231)
Employee Retirement Plan
Net Periodic Benefit Cost
Interest cost	217	$ 210
Expected return on assets	(323)	(360)
Amortization of unrealized loss	233	203
Net periodic (credit) benefit	127	53
Total benefit cost	127	53
Pension Plan
Net Periodic Benefit Cost
Interest cost	271	310
Expected return on assets	(534)	(680)
Amortization of unrealized loss	49
Net periodic (credit) benefit	(214)	(370)
Settlement loss recognized	7,231
Total benefit cost	7,017	(370)
Supplemental Employee Retirement Plan
Net Periodic Benefit Cost
Contributions to the BNB Bank Pension Plan or the Employee Retirement Plan	$ 0	$ 0