PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Components of net periodic benefit cost:
Defined benefit plan contributions	$ 300	$ 500	$ 1,300	$ 1,200
RIGP
Components of net periodic benefit cost:
Service cost	(9)	3	(26)	9
Interest cost	106	137	316	413
Expected return on plan assets	(64)	(84)	(192)	(251)
Amortization of unrecognized losses	130	211	391	632
Actuarial loss due to settlements	122	451	365	451
Net periodic benefit cost	285	718	854	1,254
Retiree Medical Plan
Components of net periodic benefit cost:
Service cost	81	92	242	274
Interest cost	327	333	982	1,000
Expected return on plan assets	0	0	0	0
Amortization of unrecognized losses	0	50	0	149
Actuarial loss due to settlements	0	0	0	0
Net periodic benefit cost	$ 408	$ 475	$ 1,224	$ 1,423