Schedule of Investments (Unaudited) - Future Contracts (Parenthetical) - Contract	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
LME Aluminum (1,418 contracts, settlement date October 19, 2015) [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts	1,418
Forward contract indexed to issuer's equity, settlement date or dates	Oct. 19, 2015
LME Copper (440 contracts, settlement date August 17, 2015) [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts	440
Forward contract indexed to issuer's equity, settlement date or dates	Aug. 17, 2015
LME Zinc (1,268 contracts, settlement date February 15, 2016) [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts	1,268
Forward contract indexed to issuer's equity, settlement date or dates	Feb. 15, 2016
LME Aluminum (1,605 contracts, settlement date October 19, 2015) [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts		1,605
Forward contract indexed to issuer's equity, settlement date or dates		Oct. 19, 2015
LME Copper (494 contracts, settlement date February 16, 2015) [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts		494
Forward contract indexed to issuer's equity, settlement date or dates		Feb. 16, 2015
LME Zinc (1,467 contracts, settlement date February 16, 2015 [Member]
Schedule of Investments [Line Items]
Open option contracts written, number of contracts		1,467
Forward contract indexed to issuer's equity, settlement date or dates		Feb. 16, 2015