Financial Highlights - Ratios to Average Limited Partners' Capital (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class A Redeemable Units [Member]
Ratios to Average Limited Partners' Capital:
Net investment loss	(4.40%)	(5.10%)	(5.70%)
Operating expenses	5.30%	5.80%	5.70%
Incentive fees	0.80%		0.20%
Total expenses	6.10%	5.80%	5.90%
Total return:
Total return before incentive fees	(6.40%)	(6.80%)	(9.50%)
Incentive fees	(0.80%)		(0.20%)
Total return after incentive fees	(7.20%)	(6.80%)	(9.70%)
Class D Redeemable Units [Member]
Ratios to Average Limited Partners' Capital:
Net investment loss	(3.20%)
Operating expenses	4.10%
Incentive fees	0.80%
Total expenses	4.90%
Total return:
Total return before incentive fees	(5.20%)
Incentive fees	(0.80%)
Total return after incentive fees	(6.00%)
Class Z Redeemable Units [Member]
Ratios to Average Limited Partners' Capital:
Net investment loss	(2.40%)
Operating expenses	3.20%
Incentive fees	0.80%
Total expenses	4.00%
Total return:
Total return before incentive fees	(4.50%)
Incentive fees	(0.80%)
Total return after incentive fees	(5.30%)