Financial Highlights - Schedule of Changes in Net Asset Value (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Per Unit Performance (for a unit outstanding throughout the period):
Net asset value per Unit, beginning of period	$ 23.82
Net asset value per Unit, end of period	23.02
Limited Partners [Member]
Per Unit Performance (for a unit outstanding throughout the period):
Net realized and unrealized gains (losses)	(0.54)	$ (0.28)
Net investment loss	(0.26)	(0.31)
Net increase (decrease) for the period	(0.80)	(0.59)
Net asset value per Unit, beginning of period	23.82	23.54
Net asset value per Unit, end of period	$ 23.02	$ 22.95