Financial Highlights - Schedule of Changes in Net Asset Value (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Per Unit Performance (for a unit outstanding throughout the period):
Net realized and unrealized gains (losses)	$ (0.14)	$ (2.53)	$ (0.48)	$ (0.45)
Net investment loss	(0.36)	(0.45)	(0.74)	(0.90)
Net increase (decrease) for the period	(0.50)	(2.98)	(1.22)	(1.35)
Net asset value per Unit, beginning of period	27.21	31.81	27.93	30.18
Net asset value per Unit, end of period	$ 26.71	$ 28.83	$ 26.71	$ 28.83