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	(3.20%)	(3.60%)	(3.90%)
Operating expense	4.80%	4.40%	3.90%
Incentive fees	0.00%	0.00%	0.20%
Total expenses	4.80%	4.40%	4.10%
Total return:
Total return before incentive fees	(9.70%)	(3.20%)	(0.50%)
Incentive fees	(0.00%)	(0.00%)	(0.20%)
Total return after incentive fees	(9.70%)	(3.20%)	(0.70%)
Class Z Redeemable Units [Member]
Ratios to Average Limited Partners' Capital:
Net investment loss	(1.20%)	(1.90%)	(2.60%)
Operating expense	2.90%	2.70%	2.60%
Incentive fees	0.00%	0.00%	0.20%
Total expenses	2.90%	2.70%	2.80%
Total return:
Total return before incentive fees	(7.90%)	(1.50%)	0.80%
Incentive fees	(0.00%)	(0.00%)	(0.20%)
Total return after incentive fees	(7.90%)	(1.50%)	0.60%