FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Per Share Operating Performance: | |||
| Net asset value, beginning of year | $ 17 | $ 26.59 | $ 42.83 |
| Total income (loss) | 3.52 | (9.41) | (15.85) |
| Net expenses | (0.13) | (0.18) | (0.39) |
| Net increase (decrease) in net asset value | 3.39 | (9.59) | (16.24) |
| Net asset value, end of year | $ 20.39 | $ 17 | $ 26.59 |
| Total Return | 19.94% | (36.07%) | (37.92%) |
| Ratios to Average Net Assets | |||
| Total income (loss) | 27.09% | (37.86%) | (34.74%) |
| Management fees | 0.60% | 0.60% | 0.60% |
| Expenses excluding management fees | 0.12% | 0.20% | 0.33% |
| Net income (loss) | 26.36% | (38.65%) | (35.66%) |