EMPLOYEE BENEFITS (Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Net periodic benefit cost
Service cost	$ 8,701	$ 6,857	$ 6,490
Interest cost	7,500	7,060	6,654
Expected return on plan assets	(10,502)	(9,650)	(7,952)
Amortization of prior service cost	0	0	0
Amortization of net loss	4,287	3,562	3,968
Net periodic benefit cost	9,986	7,829	9,160
Post-retirement Benefits
Net periodic benefit cost
Service cost	2,998	2,021	3,728
Interest cost	2,009	1,927	3,015
Expected return on plan assets	0	0	0
Amortization of prior service cost	(5,409)	(5,409)	0
Amortization of net loss	2,355	1,846	1,518
Net periodic benefit cost	$ 1,953	$ 385	$ 8,261