EMPLOYEE BENEFIT PLANS (Funded status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Nonunion Defined Benefit Pension Plan
Change in benefit obligations
Benefit obligations at beginning of period	$ 159,607	$ 174,410
Interest cost	4,572	5,200	$ 6,039
Actuarial (gain) loss	4,202	494
Benefits paid	(16,896)	(20,892)
Settlement loss	521	395
Benefit obligations at end of period	152,006	159,607	174,410
Change in plan assets
Fair value of plan assets at beginning of period	136,917	158,265
Actual return (loss) on plan assets	11,384	(506)
Employer contributions	13,400	50
Benefits paid	(16,896)	(20,892)
Fair value of plan assets at end of period	144,805	136,917	158,265
Funded status	(7,201)	(22,690)
Accumulated benefit obligation	152,006	159,607
Supplemental Benefit Plan
Change in benefit obligations
Benefit obligations at beginning of period	4,917	6,782
Interest cost	130	123	184
Actuarial (gain) loss	(7)	(47)
Benefits paid	(246)	(1,941)
Benefit obligations at end of period	4,794	4,917	6,782
Change in plan assets
Employer contributions	246	1,941
Benefits paid	(246)	(1,941)
Funded status	(4,794)	(4,917)
Accumulated benefit obligation	4,794	4,917
Postretirement Health Benefit Plan
Change in benefit obligations
Benefit obligations at beginning of period	24,616	22,116
Service cost	429	406	280
Interest cost	1,017	913	788
Actuarial (gain) loss	133	1,806
Benefits paid	(663)	(625)
Benefit obligations at end of period	25,532	24,616	$ 22,116
Change in plan assets
Employer contributions	663	625
Benefits paid	(663)	(625)
Funded status	(25,532)	(24,616)
Accumulated benefit obligation	$ 25,532	$ 24,616