COMMITMENTS AND CONTINGENCIES (Narrative) (Details) - USD ($) $ in Thousands |
3 Months Ended | ||||
|---|---|---|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Jun. 30, 2015 |
Dec. 31, 2016 |
|
| Reclamation Deposits and Surety Bonds | |||||
| Security placed with the State of Utah and BLM | $ 18,400 | $ 21,400 | |||
| Long-term restricted cash deposits | 500 | $ 3,500 | |||
| Surety bonds issued by an insurer | $ 17,900 | ||||
| Future Operating Lease Commitments | |||||
| Operating Lease, Contract Term, Maximum (in years) | 20 years | ||||
| Lease Termination Penalty | $ 1,100 | ||||
| Early Lease Termination Penalty Paid | $ 600 | $ 500 | |||
| Rental and lease expenses | $ 1,548 | ||||