Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012
Significant Accounting Policies [Line Items]
Interest earned on the Trust's average daily balances on deposit, percentage	100.00%
Percentage of interest bearing deposits	100.00%
Interest rate under deposit denominated with foreign currencies	1.00%
Wells Fargo
Significant Accounting Policies [Line Items]
Trust assets owned	25,100,000
Maximum
Significant Accounting Policies [Line Items]
Ongoing offering costs as percentage of month-end net assets, to be paid and expensed as incurred	0.50%