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
Employee benefit plans
Service cost	$ 36,002	$ 26,718	$ 29,027
Interest cost	25,741	26,966	23,994
Expected return on plan assets	(33,086)	(30,285)	(27,702)
Net amortization and deferral	17,027	10,975	16,233
Net periodic benefit cost	45,684	34,374	41,552
Other Benefits
Employee benefit plans
Service cost	7,945	7,475	8,317
Interest cost	4,305	5,441	4,873
Expected return on plan assets	(7,236)	(5,794)	(5,639)
Net amortization and deferral	197	758	1,281
Net periodic benefit cost	$ 5,211	$ 7,880	$ 8,832