COMPONENTS OF PENSION AND OTHER POSTRETIREMENT 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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 759	$ 389	$ 2,277	$ 1,166
Interest Cost	6,121	5,576	18,363	18,621
Expected Return on Plan Assets	(10,596)	(11,195)	(31,787)	(34,933)
Amortization of Prior Service Credits	(60)	(60)	(180)	(180)
Recognized Net Actuarial Loss	1,955	2,360	5,865	5,826
Settlement Loss	0	3,651	0	17,347
Net Periodic Benefit (Credit) Cost	(1,821)	721	(5,462)	7,847
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0	0	0	0
Interest Cost	5,986	6,060	17,958	18,181
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service Credits	(601)	0	(1,804)	0
Recognized Net Actuarial Loss	5,778	4,792	17,334	14,376
Settlement Loss	0	0	0	0
Net Periodic Benefit (Credit) Cost	$ 11,163	$ 10,852	$ 33,488	$ 32,557