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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 288	$ 759	$ 863	$ 2,277
Interest Cost	5,876	6,121	17,628	18,363
Expected Return on Plan Assets	(10,092)	(10,596)	(30,277)	(31,787)
Amortization of Prior Service Credits	(126)	(60)	(377)	(180)
Amortization of Actuarial Loss	2,179	1,955	6,537	5,865
Net Periodic Benefit (Credit) Cost	(1,875)	(1,821)	(5,626)	(5,462)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0	0	0
Interest Cost	4,677	5,986	14,030	17,958
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	(601)	(1,804)	(1,804)
Amortization of Actuarial Loss	4,051	5,778	12,154	17,334
Net Periodic Benefit (Credit) Cost	$ 8,127	$ 11,163	$ 24,380	$ 33,488