XML 45 R30.htm IDEA: XBRL DOCUMENT
v3.7.0.1

FINANCIAL HIGHLIGHTS (Per Unit Performance Data and Other Supplemental Financial Data) (Details) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Per Share Operating Performance: |  |  |
Net asset value, beginning of year | $ 17 | $ 26.59 | $ 42.83
Total income (loss) | 3.52 | (9.41) | (15.85)
Net expenses | (0.13) | (0.18) | (0.39)
Net increase (decrease) in net asset value | 3.39 | (9.59) | (16.24)
Net asset value, end of year | $ 20.39 | $ 17 | $ 26.59
Total Return | 19.94% | (36.07%) | (37.92%)
Ratios to Average Net Assets |  |  |
Total income (loss) | 27.09% | (37.86%) | (34.74%)
Management fees | 0.60% | 0.60% | 0.60%
Expenses excluding management fees | 0.12% | 0.20% | 0.33%
Net income (loss) | 26.36% | (38.65%) | (35.66%)

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_IncreaseDecreaseInPartnersCapitalRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Average Net Assets [Abstract] + References No definition available. + 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 (Loss). + References No definition available. + Details
Name: | usl_PercentageOfConsolidatedNetIncomeLoss
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