EMPLOYEE BENEFITS (Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Net periodic benefit cost
Service cost	$ 6,857	$ 6,490	$ 6,675
Interest cost	7,060	6,654	5,999
Expected return on plan assets	(9,650)	(7,952)	(7,800)
Amortization of prior service cost	0	0	0
Amortization of net loss	3,562	3,968	4,546
Net periodic benefit cost	7,829	9,160	9,420
Post-retirement Benefits
Net periodic benefit cost
Service cost	2,021	3,728	5,220
Interest cost	1,927	3,015	2,856
Expected return on plan assets	0	0	0
Amortization of prior service cost	(5,409)	0	0
Amortization of net loss	1,846	1,518	2,920
Net periodic benefit cost	$ 385	$ 8,261	$ 10,996