Schedule of Investments (Parenthetical)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Cash Equivalents [Member] | Us Treasury Securities [Member] | Us Treasury Bill Securities [Member]
Interest rate	0.10%	0.03%
Expiration date	17, January 2013	21, June 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG February 2013 and February 2012 contracts, expiring January 2013 and January 2012
Expiration date	January 2013	January 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG March 2013 and March 2012 contracts, expiring February 2013 and February 2012
Expiration date	February 2013	February 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG April 2013 and April 2012 contracts, expiring March 2013 and March 2012
Expiration date	March 2013	March 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG May 2013 and May 2012 contracts, expiring April 2013 and April 2012
Expiration date	April 2013	April 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG June 2013 and June 2012 contracts, expiring May 2013 and May 2012
Expiration date	May 2013	May 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG July 2013 and July 2012 contracts, expiring June 2013 and June 2012
Expiration date	June 2013	June 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG August 2013 and August 2012 contracts, expiring July 2013 and July 2012
Expiration date	July 2013	July 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG September 2013 and September 2012 contracts, expiring August 2013 and August 2012
Expiration date	August 2013	August 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG October 2013 and October 2012 contracts, expiring September 2013 and September 2012
Expiration date	September 2013	September 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG November 2013 and November 2012 contracts, expiring October 2013 and October 2012
Expiration date	October 2013	October 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG December 2013 and December 2012 contracts, expiring November 2013 and November 2012
Expiration date	November 2013	November 2012
Open Futures Contracts, Long | United State | NYMEX Natural Gas Futures NG January 2014 and January 2013 contracts, expiring December 2013 and December 2012
Expiration date	December 2013	December 2012