PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Reconciliation of Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets:
Fair value of plan assets at beginning of the period	$ 273,895
Fair value of plan assets at the end of period	233,930	$ 273,895
Pension Benefits
Change in projected benefit obligation:
Projected benefit obligation at beginning of the period	295,566	280,193
Expected administrative expenses	940	700	$ 1,870
Interest cost	10,160	9,455	9,662
Plan amendments	0	0
Participant contributions	0	0
Actuarial (gain) loss	(26,385)	27,925
Benefits paid	(7,095)	(7,617)
Benefits paid related to settlement	(29,480)	(11,969)
Loss (gain) related to settlement	893	(472)
Administrative expenses paid	(984)	(2,649)
Projected benefit obligation at end of the period	243,615	295,566	280,193
Accumulated benefit obligation at end of the period	243,615	295,566
Change in plan assets:
Fair value of plan assets at beginning of the period	273,895	263,027
Actual return on plan assets	(10,306)	33,103
Employer contributions	7,900	0
Participant contributions	0	0
Actual expenses paid	(984)	(2,649)
Benefits paid	(7,095)	(7,617)
Benefits paid related to settlement	(29,480)	(11,969)
Fair value of plan assets at the end of period	233,930	273,895	263,027
Funded status	(9,685)	(21,671)
Other Benefits
Change in projected benefit obligation:
Projected benefit obligation at beginning of the period	3,806	5,736
Expected administrative expenses	0	0	0
Interest cost	120	173	196
Plan amendments	0	(1,317)
Participant contributions	209	206
Actuarial (gain) loss	(43)	(284)
Benefits paid	(490)	(708)
Benefits paid related to settlement	0	0
Loss (gain) related to settlement	0	0
Administrative expenses paid	0	0
Projected benefit obligation at end of the period	3,602	3,806	5,736
Accumulated benefit obligation at end of the period	0	0
Change in plan assets:
Fair value of plan assets at beginning of the period	0	0
Actual return on plan assets	0	0
Employer contributions	281	502
Participant contributions	209	206
Actual expenses paid	0	0
Benefits paid	(490)	(708)
Benefits paid related to settlement	0	0
Fair value of plan assets at the end of period	0	0	$ 0
Funded status	$ (3,602)	$ (3,806)