| ASSET RETIREMENT OBLIGATIONS (Tables) | 3 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Mar. 31, 2020 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Environmental Remediation Obligations [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Summary Of Asset Retirement Obligations | The following is a summary of our asset retirement obligations: 
 
1 Includes $32.5 million and $22.0 million related to our active operations as of March 31, 2020 and December 31, 2019, respectively.
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| Schedule of Change in Asset Retirement Obligation | The following is a roll forward of our asset retirement obligation liability: 
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- References No definition available. 
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- Definition Tabular disclosure of the carrying amount of a liability for asset retirement obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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