BENEFIT PLANS (Components of Net Periodic Benefit Cost, Amounts Recognized in Other Comprehensive Income, Weighted-Average Assumptions) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of Net Periodic Benefit Cost
Service cost		$ 4,851	$ 4,157
Interest cost		44,065	44,392
Pension Plans, Defined Benefit [Member]
Components of Net Periodic Benefit Cost
Service cost		4,851	4,157	$ 21,904
Interest cost		44,065	44,392	40,995
Expected return on plan assets		(54,736)	(50,802)	(47,425)
Settlement charge		2,031	0	0
Curtailment gain (loss)		0	0	855
Amortization of prior service cost		48	188	339
Amortization of actuarial loss		21,641	11,221	20,429
Net periodic pension/postretirement benefit cost		17,900	9,156	37,097
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)		(3,615)	118,915	(163,205)
Prior service cost (credit)		0	0	(583)
Reclassification of actuarial loss to net periodic postretirement benefit cost		(23,672)	(11,221)	(20,429)
Reclassification of prior service cost to net periodic pension benefit cost		(48)	(188)	(1,194)
Amount recognized in other comprehensive income		(27,335)	107,506	(185,411)
Amount recognized in net periodic pension benefit cost and other comprehensive income		$ (9,435)	$ 116,662	$ (148,314)
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate		4.14%	4.91%	4.33%
Expected return on plan assets		7.50%	7.50%	7.50%
Rate of compensation increase (for salary-related plans)		3.70%	3.50%	3.50%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate		4.54%	4.14%	4.91%
Rate of compensation increase (for salary-related plans)		3.50%	3.70%	3.50%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of Net Periodic Benefit Cost
Service cost		$ 1,894	$ 2,146	$ 2,830
Interest cost		2,485	3,297	3,260
Curtailment gain (loss)	$ (3,832)	0	(3,832)	0
Amortization of prior service cost		(4,232)	(4,327)	(4,863)
Amortization of actuarial loss		37	227	1,372
Net periodic pension/postretirement benefit cost		184	(2,489)	2,599
Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income
Net actuarial loss (gain)		(35,209)	(5,256)	(20,444)
Reclassification of actuarial loss to net periodic postretirement benefit cost		(37)	(227)	(1,372)
Reclassification of prior service cost to net periodic pension benefit cost		4,232	8,159	4,863
Amount recognized in other comprehensive income		(31,014)	2,676	(16,953)
Amount recognized in net periodic pension benefit cost and other comprehensive income		$ (30,830)	$ 187	$ (14,354)
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for next year			7.50%	7.50%
Rate to which the cost trend rate gradually declines			5.00%	5.00%
Year that the rate reaches the rate it is assumed to maintain			2025	2019
Weighted-average assumptions used to determine net periodic benefit cost for years ended December 31
Discount rate		3.50%	4.10%	3.30%
Weighted-average assumptions used to determine benefit obligation at December 31
Discount rate		3.69%	3.50%	4.10%