Dec. 06, 2007

Organization and Business (Additional Information) (Details) (USD $)	0 Months Ended
	Dec. 04, 2007	Dec. 06, 2007	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets			350usl_FeePaidPerOrder
Number of initially registered units on Form S-1 with the U.S. Securities and Exchange Commission	11,000,000usl_NumberOfUnitsRegisteredInPeriod
Net asset value per share		$ 50.00usl_NetAssetValuePerUnit	$ 26.59usl_NetAssetValuePerUnit	$ 42.83usl_NetAssetValuePerUnit	$ 39.81usl_NetAssetValuePerUnit	$ 43.46usl_NetAssetValuePerUnit
Number of shares issued		300,000
Value of shares issued		$ 15,000,000
Number of registered shares			100,000,000usl_NumberOfRegisteredUnits
Commenced investment operations date		Dec. 06, 2007
Creation Baskets
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of shares per basket			50,000
Open Futures Contracts, Long \| United States
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of Contracts			658
Beginning on January 1, 2013 and after
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets			1,000