COMPONENTS OF PENSION AND OTHER POST-EMPLOYMENT BENEFIT (OPEB) PLANS NET PERIODIC BENEFIT COSTS - Schedule of Components of Net Periodic Benefit (Credit) Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 288	$ 737
Interest Cost	5,876	6,316
Expected Return on Plan Assets	(10,092)	(10,596)
Amortization of Prior Service Credits	(126)	(126)
Amortization of Actuarial Loss	2,179	2,224
Net Periodic Benefit (Credit) Cost	(1,875)	(1,445)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	4,677	5,986
Expected Return on Plan Assets	0	0
Amortization of Prior Service Credits	(601)	(601)
Amortization of Actuarial Loss	4,051	5,778
Net Periodic Benefit (Credit) Cost	$ 8,127	$ 11,163