FINANCIAL HIGHLIGHTS (Per share Performance Data and Other Supplemental Financial Data) (Detail) - $ / shares	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Per Share Operating Performance:
Net asset value, beginning of year	$ 11.02	$ 20.15	$ 35.23
Total income (loss)	0.77	(9.01)	(14.85)
Total expenses	(0.08)	(0.12)	(0.23)
Net increase (decrease) in net asset value	0.69	(9.13)	(15.08)
Net asset value, end of year	$ 11.71	$ 11.02	$ 20.15
Total Return	6.26%	(45.31%)	(42.80%)
Ratios to Average Net Assets
Total income (loss)	20.57%	(49.08%)	(68.15%)
Expenses excluding management fees	0.32%	0.29%	0.27%
Management fees	0.45%	0.45%	0.45%
Net income (loss)	19.80%	(49.82%)	(68.86%)