EMPLOYEE BENEFIT PLANS - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans
Components of net periodic benefit cost:
Interest cost	$ 0	$ 0	$ 816
Actuarial (loss) gain amortization	0	0	737
Settlement charge	0	3,325	29,767
Net periodic expense	0	3,325	31,320
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	70	94	392
Interest cost	227	223	466
Expected long-term return on assets	(249)	(316)	(457)
Prior service cost amortization	(454)	(465)	0
Actuarial (loss) gain amortization	10	0	0
Settlement charge	0	45	0
Curtailment gain	0	(816)	0
Net periodic expense	$ (396)	$ (1,235)	$ 401