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, 2019	Mar. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 987	$ 288
Interest Cost	6,275	5,876
Expected Return on Plan Assets	(10,114)	(10,092)
Amortization of Prior Service Credits	(92)	(126)
Amortization of Actuarial Loss	1,490	2,179
Net Periodic Benefit (Credit) Cost	(1,454)	(1,875)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0
Interest Cost	4,580	4,677
Expected Return on Plan Assets	0	0
Amortization of Prior Service Credits	(601)	(601)
Amortization of Actuarial Loss	2,315	4,051
Net Periodic Benefit (Credit) Cost	$ 6,294	$ 8,127