EMPLOYEE BENEFITS (Obligation and Funded Status) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Reconciliation of benefit obligation
Benefit obligation at beginning of year	$ 171,876	$ 160,390
Service cost	6,857	6,490	$ 6,675
Interest cost	7,060	6,654	5,999
Actuarial loss	26,963	2,215
Adjustment for plan amendment	0	0
Benefit payments	(4,407)	(3,873)
Benefit obligation at end of year	208,349	171,876	160,390
Reconciliation of fair value of plan assets
Fair value of plan assets at beginning of year	128,430	106,600
Actual return on plan assets	22,225	9,320
Employer contributions	11,396	16,383
Benefit payments	(4,407)	(3,873)
Fair value of plan assets at end of year	157,644	128,430	106,600
Funded status at end of year	(50,705)	(43,446)
Accumulated pension benefit obligation	184,436	152,620
Post-retirement Benefits
Reconciliation of benefit obligation
Benefit obligation at beginning of year	46,785	72,175
Service cost	2,021	3,728	5,220
Interest cost	1,927	3,015	2,856
Actuarial loss	6,326	1,468
Adjustment for plan amendment	0	(32,289)
Benefit payments	(1,331)	(1,312)
Benefit obligation at end of year	55,728	46,785	72,175
Reconciliation of fair value of plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	1,331	1,311
Benefit payments	(1,331)	(1,311)
Fair value of plan assets at end of year	0	0	$ 0
Funded status at end of year	$ (55,728)	$ (46,785)