PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES (Schedule of Depreciation, Depletion, and Accretion) (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Mar. 31, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Property, Plant and Equipment [Abstract] | |||||
| Depreciation | $ 7,587 | $ 18,893 | $ 28,931 | $ 56,257 | |
| Depletion | 727 | 1,038 | 2,708 | 3,499 | |
| Accretion | 442 | $ 424 | 424 | 1,326 | 1,272 |
| Total incurred | $ 8,756 | $ 20,355 | $ 20,355 | $ 32,965 | $ 61,028 |