EMPLOYEE BENEFIT PLANS (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014 USD ($) person	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Amounts recognized in the consolidated balance sheets
Noncurrent liabilities (included in pension and postretirement liabilities)		$ (51,241)	$ (42,418)
Components of net periodic benefit cost
Pension settlement expense		3,202	6,595	$ 2,111
Nonunion Defined Benefit Pension Plan
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans
Curtailment gain or loss recognized in earnings				0
Number of plan participants for which vested pension benefits were settled | person	375
Premium paid to purchase nonparticipating annuity contract	$ 25,400		25,400
Pension benefit obligation settled with nonparticipating annuity contract	23,300
Lump-sum distributions			32,100
Unrecognized net actuarial loss		$ 28,457	24,303
Amortization period for unrecognized net actuarial loss		8 years
Change in benefit obligations
Benefit obligations at beginning of period	211,660	$ 174,410	211,660
Service cost				4,734
Interest cost		5,200	6,039	7,784
Actuarial (gain) loss		494	11,906
Benefits paid		(20,892)	(58,047)
Settlement loss		395	2,852
Benefit obligations at end of period		159,607	174,410	211,660
Change in plan assets
Fair value of plan assets at beginning of period	207,613	158,265	207,613
Actual loss on plan assets		(506)	8,599
Employer contributions		50	100
Benefits paid		(20,892)	(58,047)
Fair value of plan assets at end of period		136,917	158,265	207,613
Funded status		(22,690)	(16,145)
Accumulated benefit obligation		159,607	174,410
Amounts recognized in the consolidated balance sheets
Noncurrent liabilities (included in pension and postretirement liabilities)		(22,690)	(16,145)
Liabilities recognized		(22,690)	(16,145)
Components of net periodic benefit cost
Service cost				4,734
Interest cost		5,200	6,039	7,784
Expected return on plan assets		(9,180)	(10,419)	(13,313)
Pension settlement expense		3,202	5,880	2,111
Amortization of net actuarial loss		3,218	2,398	7,140
Net periodic benefit cost		2,440	3,898	8,456
Supplemental Benefit Plan
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans
Unrecognized net actuarial loss		1,001	1,207
Change in benefit obligations
Benefit obligations at beginning of period	7,092	6,782	7,092
Interest cost		123	184	150
Actuarial (gain) loss		(47)	53
Benefits paid		(1,941)	(853)
Settlement loss			306
Benefit obligations at end of period		4,917	6,782	7,092
Change in plan assets
Employer contributions		1,941	853
Benefits paid		(1,941)	(853)
Funded status		(4,917)	(6,782)
Accumulated benefit obligation		4,917	6,782
Amounts recognized in the consolidated balance sheets
Current liabilities (included in accrued expenses)		(246)	(1,941)
Noncurrent liabilities (included in pension and postretirement liabilities)		(4,671)	(4,841)
Liabilities recognized		(4,917)	(6,782)
Components of net periodic benefit cost
Interest cost		123	184	150
Pension settlement expense			715
Amortization of net actuarial loss		159	214	260
Net periodic benefit cost		282	1,113	410
Postretirement Health Benefit Plan
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans
Unrecognized net actuarial loss		$ 6,280	5,327
Unrecognized prior service credit, amortization period		8 years
Change in benefit obligations
Benefit obligations at beginning of period	$ 16,318	$ 22,116	16,318
Service cost		406	280	331
Interest cost		913	788	751
Actuarial (gain) loss		1,806	5,269
Benefits paid		(625)	(539)
Benefit obligations at end of period		24,616	22,116	16,318
Change in plan assets
Employer contributions		625	539
Benefits paid		(625)	(539)
Funded status		(24,616)	(22,116)
Accumulated benefit obligation		24,616	22,116
Amounts recognized in the consolidated balance sheets
Current liabilities (included in accrued expenses)		(736)	(684)
Noncurrent liabilities (included in pension and postretirement liabilities)		(23,880)	(21,432)
Liabilities recognized		(24,616)	(22,116)
Components of net periodic benefit cost
Service cost		406	280	331
Interest cost		913	788	751
Amortization of prior service credit		(190)	(190)	(190)
Amortization of net actuarial loss		853	93	535
Net periodic benefit cost		$ 1,982	$ 971	$ 1,427