POSTRETIREMENT MEDICAL BENEFITS AND PENSION - Pension Benefit Disclosures (Details) - Pension - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 376	$ 500	$ 882	$ 1,000
Interest cost	1,971	1,638	3,957	3,384
Expected return on plan assets	(2,680)	(2,154)	(5,319)	(4,307)
Pension settlement accounting	(347)	0	(347)	0
Amortization of deferred items	1,140	359	2,250	719
Total net periodic benefit cost	$ 460	$ 343	1,423	$ 796
Employer contributions during the period			3,300
Expected employer contributions to pension plans during the remainder of the year			$ 500