PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Funded status) (Details) - Nonunion Defined Benefit Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Change in benefit obligations
Benefit obligations at beginning of period	$ 137,417
Interest cost	1,015	$ 1,240
Actuarial gain	(3,487)
Benefits paid	(4,864)
Benefit obligations at end of period	130,081
Change in plan assets
Fair value of plan assets at beginning of period	124,831
Actual return on plan assets	402
Benefits paid	(4,864)
Fair value of plan assets at end of period	120,369
Funded status at period end	(9,712)
Accumulated benefit obligation	$ 130,081
Adjusted funding target attainment percentage			112.97%