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
	Mar. 31, 2014	Mar. 31, 2013
Postretirement Medical Benefits
Components of net periodic benefit cost:
Service cost	$ 822	$ 1,109
Interest cost	3,203	3,035
Amortization of deferred items	5	1,001
Total net periodic benefit cost	$ 4,030	$ 5,145