PENSION AND POST RETIREMENT BENEFIT PLANS - Net Periodic Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest and service cost	$ 1,995	$ 2,138	$ 3,990	$ 4,276
Expected return on plan assets	(3,443)	(3,342)	(6,886)	(6,684)
Amortization of net loss	826	830	1,652	1,660
Net periodic benefit	$ (622)	$ (374)	$ (1,244)	$ (748)