POSTRETIREMENT MEDICAL BENEFITS AND PENSION - Pension Benefit Disclosures (Details) - Pension - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 436	$ 500	$ 1,318	$ 1,500
Interest cost	1,831	1,747	5,780	5,240
Expected return on plan assets	(2,435)	(2,154)	(7,744)	(6,461)
Pension settlement accounting	(1,529)	0	(1,874)	0
Amortization of deferred items	1,059	359	3,301	1,078
Total net periodic benefit cost	$ (638)	$ 452	781	$ 1,357
Employer contributions during the period			3,500
Expected employer contributions to pension plans during the remainder of the year			$ 300