POSTRETIREMENT BENEFIT PLANS - Components of cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Components of net periodic benefit cost (credit)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income	Other, net	Other, net	Other, net	Other, net
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income	Other, net	Other, net	Other, net	Other, net
Supplemental Benefit Plan
Components of net periodic benefit cost (credit)
Interest cost	$ 1	$ 1	$ 3	$ 2
Amortization of net actuarial (gain) loss	2	3	4	5
Net periodic benefit cost (credit)	3	4	7	7
Postretirement Health Benefit Plan
Components of net periodic benefit cost (credit)
Service cost	39	48	78	96
Interest cost	110	107	220	214
Amortization of net actuarial (gain) loss	(191)	(137)	(382)	(274)
Net periodic benefit cost (credit)	$ (42)	$ 18	$ (84)	$ 36