EMPLOYEE BENEFIT PLANS - Components of cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of net periodic benefit cost
Pension settlement expense		$ 89	$ 8,505
Nonunion Defined Benefit Pension Plan
Components of net periodic benefit cost
Interest cost			624
Expected return on plan assets			(31)
Pension settlement expense			4,164
Amortization of net actuarial (gain) loss			260
Net periodic benefit cost			5,017
Noncash charge to pension settlement expense			4,000
Supplemental Benefit Plan
Components of net periodic benefit cost
Interest cost	$ 4	9	39
Pension settlement expense		89	370
Amortization of net actuarial (gain) loss	9	8	95
Net periodic benefit cost	13	106	504
Postretirement Health Benefit Plan
Components of net periodic benefit cost
Service cost	192	187	320
Interest cost	427	576	1,212
Amortization of prior service credit		(1)	(33)
Amortization of net actuarial (gain) loss	(548)	(597)	898
Net periodic benefit cost	$ 71	$ 165	$ 2,397