POSTRETIREMENT MEDICAL BENEFITS AND PENSION - Postretirement Medicial Benefit Obligations Balance Sheet Disclosures (Details) (Postretirement Medical Benefits, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Postretirement Medical Benefits
Components of net periodic benefit cost:
Service cost	$ 822	$ 1,109	$ 1,645	$ 2,218
Interest cost	3,203	3,035	6,407	6,069
Amortization of deferred items	4	1,001	9	2,003
Total net periodic benefit cost	$ 4,029	$ 5,145	$ 8,061	$ 10,290