XML 26 R28.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Financial Highlights (Per Unit Performance Data and Other Supplemental Financial Data) (Details) (USD $) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2009 | Dec. 06, 2007
Per Unit Operating Performance: |  |  |  |  |
Net Asset Value Per Share, Beginning | $ 39.81 | $ 43.46 | $ 42.91 | $ 42.91 | $ 50.00
Total income (loss) | $ 3.43 | $ (3.32) | $ 0.88 |  |
Net expenses | $ (0.41) | $ (0.33) | $ (0.33) |  |
Net increase (decrease) in net asset value | $ 3.02 | $ (3.65) | $ 0.55 |  |
Net Asset Value Per Share, Ending | $ 42.83 | $ 39.81 | $ 43.46 | $ 42.91 | $ 50.00
Total Return | 7.59% | (8.40%) | 1.28% |  |
Ratios to Average Net Assets |  |  |  |  |
Total income (loss) | 7.54% | (6.94%) | 2.08% |  |
Management fees | 0.60% | 0.60% | 0.60% |  |
Expenses excluding management fees | 0.39% | 0.18% | 0.17% |  |
Net income (loss) | 6.55% | (7.72%) | 1.31% |  |

X
- Details
Name: | us-gaap_IncreaseDecreaseInPartnersCapitalRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition Expenses, Excluding Management Fee Percentage + References No definition available. + Details
Name: | usl_ExpensesExcludingManagementFeePercentage
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Increase (Decrease) In Net Asset Value Per Unit + References No definition available. + Details
Name: | usl_IncreaseDecreaseInNetAssetValuePerUnit
Namespace Prefix: | usl_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Management Incentive Fee Percentage + References No definition available. + Details
Name: | usl_ManagementIncentiveFeePercentage
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net asset value per unit. + References No definition available. + Details
Name: | usl_NetAssetValuePerUnit
Namespace Prefix: | usl_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of Consolidated Net Income + References No definition available. + Details
Name: | usl_PercentageOfConsolidatedNetIncome
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of Total Revenue + References No definition available. + Details
Name: | usl_PercentageOfTotalRevenue
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Rate Of Return On Average Asset + References No definition available. + Details
Name: | usl_RateOfReturnOnAverageAsset
Namespace Prefix: | usl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total Expenses, Per Unit + References No definition available. + Details
Name: | usl_TotalExpensesPerUnit
Namespace Prefix: | usl_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total Income (Loss), Per Unit + References No definition available. + Details
Name: | usl_TotalIncomeLossPerUnit
Namespace Prefix: | usl_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration