POSTRETIREMENT MEDICAL BENEFITS Expected Future Cash Flows (Details) - Postretirement Medical Benefits [Member] $ in Thousands	Dec. 31, 2016 USD ($)
Expected future payments, postretirement medical benefits:
2017 - Postretirement Medical Benefits	$ 16,462
2018 - Postretirement Medical Benefits	16,794
2019 - Postretirement Medical Benefits	17,354
2020 - Postretirement Medical Benefits	17,929
2021 - Postretirement Medical Benefits	18,374
Years 2022 - 2026 - Postretirement Medical Benefits	97,014
Expected future receipts, Medicare D Subsidy:
2017 - Medicare D Subsidy	(1,570)
2018 - Medicare D Subsidy	(1,638)
2019 - Medicare D Subsidy	(1,700)
2020 - Medicare D Subsidy	(1,759)
2021 - Medicare D Subsidy	(1,818)
Years 2022 - 2026 - Medicare D Subsidy	(9,708)
Expected future payments, net
2017 - Net Postretirement Medical Benefits	14,892
2018 - Net Postretirement Medical Benefits	15,156
2019 - Net Postretirement Medical Benefits	15,654
2020 - Net Postretirement Medical Benefits	16,170
2021 - Net Postretirement Medical Benefits	16,556
Years 2022 - 2026 - Net Postretirement Medical Benefits	$ 87,306