Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Restricted for maintenance margin	$ 32,903,175	$ 34,998,099
US Treasury Bill Securities [Member]
United States Treasury Obligations, cost	$ 768,709,369	$ 1,077,885,299

Amount of right to receive cash and securities on deposit with broker-dealers to demonstrate an intention to complete a purchase (good faith deposit) and collateral deposited by counterparty to cover the credit risk assumed (margin deposit).

No definition available.

Name:	us-gaap_GoodFaithAndMarginDepositsWithBrokerDealers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant