XML 76 R21.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Summary of Significant Accounting Policies (Additional Information) (Details) |  |  | 6 Months Ended
--- | --- | --- | ---
Jun. 30, 2013 | Feb. 29, 2012 Creation Baskets [Member] | Feb. 29, 2012 Redemption Baskets [Member] | Feb. 29, 2012 Prior to February 29, 2012 [Member] Creation Baskets [Member] | Feb. 29, 2012 Prior to February 29, 2012 [Member] Redemption Baskets [Member] | Jun. 30, 2013 Maximum [Member]
Significant Accounting Policies [Line Items] |  |  |  |  |  |
Minimum likelihood of tax benefits being recognized upon ultimate settlement | 50.00% |  |  |  |  |
Number of units per basket |  | 50,000 | 50,000 | 100,000 | 100,000 |
Cash equivalents maturity period |  |  |  |  |  | 6 months

X
- Definition Cash Equivalents, Maturity Period + References No definition available. + Details
Name: | usl_CashEquivalentsMaturityPeriod
Namespace Prefix: | usl_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Units per Basket + References No definition available. + Details
Name: | usl_NumberOfUnitsPerBasket
Namespace Prefix: | usl_
Data Type: | us-types:perUnitItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage Of Income Tax Examination Minimum Likelihood of Tax Benefits Being Realized Upon Settlement + References No definition available. + Details
Name: | usl_PercentageOfIncomeTaxExaminationMinimumLikelihoodOfTaxBenefitsBeingRealizedUponSettlement
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | usl_SignificantAccountingPoliciesLineItems
Namespace Prefix: | usl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration