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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 288	$ 759	$ 575	$ 1,518
Interest Cost	5,876	6,121	11,752	12,242
Expected Return on Plan Assets	(10,092)	(10,596)	(20,185)	(21,191)
Amortization of Prior Service Credits	(126)	(60)	(251)	(120)
Amortization of Actuarial Loss	2,179	1,955	4,358	3,910
Net Periodic Benefit (Credit) Cost	(1,875)	(1,821)	(3,751)	(3,641)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0	0	0
Interest Cost	4,677	5,986	9,353	11,972
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	(601)	(1,202)	(1,203)
Amortization of Actuarial Loss	4,051	5,778	8,102	11,556
Net Periodic Benefit (Credit) Cost	$ 8,127	$ 11,163	$ 16,253	$ 22,325