EMPLOYEE BENEFIT PLANS - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	2,706	3,197	3,021
Expected return on plan assets	(3,504)	(3,107)	(3,934)
Amortization of losses (gains)	861	449	673
Net periodic benefit cost (credit)	63	539	(240)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	6	7
Interest cost	51	54	38
Expected return on plan assets	0	0	0
Amortization of losses (gains)	8	0	2
Net periodic benefit cost (credit)	$ 65	$ 60	$ 47