| **CONCENTRATION OF RISK Other accrued expenses (Details) - USD ($) $ in Thousands** | Dec. 31, 2017 | Dec. 31, 2016 |
|-------------------------------------------------------------------------------------|---------------|---------------|
| **Risks and Uncertainties [Abstract]**                                              |          |          |
| Accrued Employee Benefits                                                           | $ 22,383      | $ 22,282      |
| Asset Retirement Obligation, Current                                                | 15,801        | 9,775         |
| Accrued Environmental Liabilities                                                   | 1,374         | 3,238         |
| Other Accrued Liabilities                                                           | 3,429         | 3,330         |
| Other Accrued Liabilities, Noncurrent                                               | $ 42,987      | $ 38,625      |

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| - Definition
Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).
+ References
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| - Definition
Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.
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| - Definition
Amount of expenses incurred but not yet paid classified as other.
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| - Definition
Amount of expenses incurred but not yet paid classified as other, due after one year or the normal operating cycle, if longer.
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No definition available.
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