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FINANCIAL HIGHLIGHTS (Per share Performance Data and Other Supplemental Financial Data) (Detail) - $ / shares
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Per Share Operating Performance:    
Net asset value, beginning of year $ 11.02 $ 20.15
Total income (loss) (1.26) (3.25)
Total expenses (0.02) (0.03)
Net increase (decrease) in net asset value (1.28) (3.28)
Net asset value, end of year $ 9.74 $ 16.87
Total Return (11.62%) (16.28%)
Ratios to Average Net Assets    
Total income (loss) (4.91%) (11.82%)
Management fees [1] 0.45% 0.45%
Expenses excluding management fees [1] 0.37% 0.27%
Net income (loss) (5.11%) (12.00%)
[1] Annualized.