EMPLOYEE BENEFITS (Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Net periodic benefit cost
Service cost	$ 10,829	$ 7,989	$ 8,701
Interest cost	8,266	8,320	7,500
Expected return on plan assets	(13,539)	(10,784)	(10,502)
Amortization of prior service cost	0	0	0
Amortization of net loss	3,914	3,603	4,287
Net periodic benefit cost	9,470	9,128	9,986
Post-retirement Benefits
Net periodic benefit cost
Service cost	1,728	1,823	2,998
Interest cost	1,014	1,274	2,009
Expected return on plan assets	0	0	0
Amortization of prior service cost	(8,084)	(8,684)	(5,409)
Amortization of net loss	375	894	2,355
Net periodic benefit cost	$ (4,967)	$ (4,693)	$ 1,953