PENSION AND OTHER POSTRETIREMENT BENEFITS - NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Defined Benefit Plan, Estimated Percentage of Employees to be Entitled to Annuity Payments Upon Retirement	43.00%
Pension Plan [Member]
Net periodic benefit cost [Abstract]
Service Cost	$ 5,337	$ 4,510	$ 5,421
Interest Cost	11,168	10,735	9,439
Expected Return on Plan Assets	(14,789)	(13,491)	(11,914)
Amortizations:
Prior Service Cost (Credits)	212	175	251
Actuarial Loss	10,608	5,716	9,006
Net Periodic Benefit Cost	12,536	7,645	12,203
Capitalized Benefit Costs	(4,805)	(3,047)	(5,002)
Deferred Benefit Costs	(1,007)	0	0
Total Net Periodic Benefit Expense	6,724	4,598	7,201
Other Postretirement Benefits [Member]
Net periodic benefit cost [Abstract]
Service Cost	1,116	891	1,139
Interest Cost	2,973	2,852	2,730
Expected Return on Plan Assets	(2,993)	(2,603)	(2,378)
Amortizations:
Prior Service Cost (Credits)	608	152	(283)
Actuarial Loss	1,342	974	1,738
Net Periodic Benefit Cost	3,046	2,266	2,946
Capitalized Benefit Costs	(1,043)	(722)	(1,172)
Deferred Benefit Costs	(256)	0	0
Total Net Periodic Benefit Expense	$ 1,747	$ 1,544	$ 1,774