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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 987	$ 288	$ 1,975	$ 575
Interest Cost	6,275	5,876	12,551	11,752
Expected Return on Plan Assets	(10,114)	(10,092)	(20,229)	(20,185)
Amortization of Prior Service Credits	(92)	(126)	(183)	(251)
Amortization of Actuarial Loss	1,490	2,179	2,979	4,358
Net Periodic Benefit (Credit) Cost	(1,454)	(1,875)	(2,907)	(3,751)
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0	0	0
Interest Cost	4,580	4,677	9,160	9,353
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	(601)	(1,203)	(1,202)
Amortization of Actuarial Loss	2,315	4,051	4,631	8,102
Net Periodic Benefit (Credit) Cost	$ 6,294	$ 8,127	$ 12,588	$ 16,253