BENEFIT PLANS (Combined Funded Status of Plans and their Reconciliation with Related Amounts Recognized in Consolidated Financial Statements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in Benefit Obligation
Projected benefit obligation at beginning of year	$ 1,083,222	$ 911,700
Service cost	4,851	4,157
Interest cost	44,065	44,392
Actuarial (gain) loss	(63,725)	167,041
Benefits paid	(79,960)	(44,068)
Projected benefit obligation at end of year	988,453	1,083,222	$ 911,700
Change in Plan Assets
Fair value of assets at beginning of year	816,972	756,624
Actual return on plan assets	(5,373)	98,928
Employer contributions	14,047	5,488	4,855
Benefits paid	(79,960)	(44,068)
Fair value of assets at end of year	745,686	816,972	756,624
Funded status	(242,767)	(266,250)
Amounts Recognized in the Consolidated Balance Sheets
Noncurrent assets	0	0
Current liabilities	(9,106)	(13,719)
Noncurrent liabilities	(233,661)	(252,531)
Net amount recognized	(242,767)	(266,250)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial (gain) loss	222,580	249,867
Prior service credit	(404)	(356)
Total amount recognized	222,176	249,511
Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in Benefit Obligation
Projected benefit obligation at beginning of year	85,336	92,888
Service cost	1,894	2,146	2,830
Interest cost	2,485	3,297	3,260
Liability reduction from curtailment	0	(2,639)
Actuarial (gain) loss	(35,195)	(2,617)
Benefits paid	(5,915)	(7,739)	(6,258)
Projected benefit obligation at end of year	48,605	85,336	92,888
Change in Plan Assets
Fair value of assets at beginning of year	0	0
Actual return on plan assets	0	0
Benefits paid	(5,915)	(7,739)	(6,258)
Fair value of assets at end of year	0	0	$ 0
Funded status	(48,605)	(85,336)
Amounts Recognized in the Consolidated Balance Sheets
Current liabilities	(6,287)	(8,964)
Noncurrent liabilities	(42,318)	(76,372)
Net amount recognized	(48,605)	(85,336)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial (gain) loss	(24,325)	10,921
Prior service credit	(23,928)	(28,160)
Total amount recognized	$ (48,253)	$ (17,239)