Financial Highlights - Changes in Net Asset Value (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financial Highlights [Line Items]
Net realized and unrealized gains (losses)	$ (162.07)	$ (162.92)	$ 171.90
Interest income	0.83	0.52	1.66
Expenses	(40.40)	(44.73)	(56.07)
Increase (decrease) for the year	(201.64)	(207.13)	117.49
Net asset value per unit, beginning of year	1,803.82	2,010.95	1,893.46
Net asset value per unit, end of period	1,602.18	1,803.82	2,010.95