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Condensed Schedule of Investments (Parenthetical) (United State [Member]) | 3 Months Ended
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Mar. 31, 2013
Cash Equivalents [Member] | Us Treasury Securities [Member] | Us Treasury Bill Securities [Member] |
Interest rate | 0.08%
Expiration date | 5/30/2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG May 2013 contracts, expiring April 2013 [Member] |
Expiration date | April 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG June 2013 contracts, expiring May 2013 [Member] |
Expiration date | May 2013
Open Futures Contracts, Long [Member] | NYMEX Natural Gas Futures NG July 2013 contracts, expiring June 2013 [Member] |
Expiration date | June 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

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- Definition Interest rate stated in the contractual debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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