Share Purchases and Redemptions - Additional Information (Detail)	6 Months Ended
Jun. 30, 2014 Basket
Equity [Abstract]
Minimum number of Baskets that can be purchased	1
Shares Redeemed	200,000
Minimum number of Baskets that can be redeemed	1

Number of stock bought back by the entity at the exercise price or redemption price.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Name:	us-gaap_StockRedeemedOrCalledDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration