PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Components of net periodic benefit cost:
Defined benefit plan contributions	$ 800	$ 200
RIGP
Components of net periodic benefit cost:
Service cost	(9)	3
Interest cost	127	138
Expected return on plan assets	(71)	(84)
Amortization of unrecognized losses	145	211
Net periodic benefit cost	192	268
Retiree Medical Plan
Components of net periodic benefit cost:
Service cost	91	91
Interest cost	333	333
Expected return on plan assets	0	0
Amortization of unrecognized losses	50	50
Net periodic benefit cost	$ 474	$ 474