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Condensed Schedule of Investments (Parenthetical) | 6 Months Ended
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Jun. 30, 2013
Cash Equivalents [Member] | Us Treasury Securities [Member] | Us Treasury Bill Securities [Member] |
Interest rate | 0.06%
Expiration date | 11/21/2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG August 2013 contracts, expiring July 2013 [Member] |
Expiration date | July 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG September 2013 contracts, expiring August 2013 [Member] |
Expiration date | August 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG October 2013 contracts, expiring September 2013 [Member] |
Expiration date | September 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG November 2013 contracts, expiring October 2013 [Member] |
Expiration date | October 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG December 2013 contracts, expiring November 2013 [Member] |
Expiration date | November 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG January 2014 contracts, expiring December 2013 [Member] |
Expiration date | December 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG February 2014 contracts, expiring January 2014 [Member] |
Expiration date | January 2014
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG March 2014 contracts, expiring February 2014 [Member] |
Expiration date | February 2014
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG April 2014 contracts, expiring March 2014 [Member] |
Expiration date | March 2014
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG May 2014 contracts, expiring April 2014 [Member] |
Expiration date | April 2014
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG June 2014 contracts, expiring May 2014 [Member] |
Expiration date | May 2014
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG July 2014 contracts, expiring June 2014 [Member] |
Expiration date | June 2014

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