SUMMARY OF PRINCIPAL ACCOUNTING POLICIES (Assets retirement obligation, Prepaid Land Use Right and Impairment of Long-Lived Assets) (Narrative) (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Impairment of long-lived assets | |||
| Impairment charge of long-lived assets | $ 0 | $ 0 | $ 0 |