EMPLOYEE BENEFITS (Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Net periodic benefit cost
Service cost	$ 7,989	$ 8,701	$ 6,857
Interest cost	8,320	7,500	7,060
Expected return on plan assets	(10,784)	(10,502)	(9,650)
Amortization of prior service cost	0	0	0
Amortization of net loss	3,603	4,287	3,562
Net periodic benefit cost	9,128	9,986	7,829
Post-retirement Benefits
Net periodic benefit cost
Service cost	1,823	2,998	2,021
Interest cost	1,274	2,009	1,927
Expected return on plan assets	0	0	0
Amortization of prior service cost	(8,684)	(5,409)	(5,409)
Amortization of net loss	894	2,355	1,846
Net periodic benefit cost	$ (4,693)	$ 1,953	$ 385