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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Postretirement Medical Benefits
Components of net periodic benefit cost:
Service cost	$ 822	$ 1,109	$ 2,467	$ 3,327
Interest cost	3,203	3,035	9,610	9,104
Amortization of deferred items	4	1,001	13	3,004
Total net periodic benefit cost	$ 4,029	$ 5,145	$ 12,090	$ 15,435