ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and postretirement plans:
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 332	$ (1,601)	$ (19,828)
Prior service cost
Pension and postretirement plans:
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	454	465	0
Actuarial losses
Pension and postretirement plans:
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(10)	(3,058)	(30,504)
Pension and Postretirement Plans
Pension and postretirement plans:
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	444	(2,593)	(30,504)
Income tax (expense) benefit	(112)	992	10,676
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 332	$ (1,601)	$ (19,828)