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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014
Significant Accounting Policies [Line Items] |
Minimum likelihood of tax benefits being recognized upon ultimate settlement | 50.00%unl_PercentageOfIncomeTaxExaminationMinimumLikelihoodOfTaxBenefitsBeingRealizedUponSettlement
Recognized interest income expense and penalties related to unrecognized tax benefits | $ 0 unl_RecognizedInterestIncomeExpenseAndPenaltiesRelatedToUnrecognizedTaxBenefits
Redemption Baskets [Member] |
Significant Accounting Policies [Line Items] |
Number of units per basket | 50,000 unl_NumberOfUnitsPerBasket / invest_InvestmentSecuritiesClassAxis = unl_RedemptionBasketsMember
Maximum [Member] |
Significant Accounting Policies [Line Items] |
Cash equivalents maturity period | 6 months

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

X
- Definition Number of Units per Basket + References No definition available. + Details
Name: | unl_NumberOfUnitsPerBasket
Namespace Prefix: | unl_
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: | unl_PercentageOfIncomeTaxExaminationMinimumLikelihoodOfTaxBenefitsBeingRealizedUponSettlement
Namespace Prefix: | unl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Recognized interest income expense and penalties related to unrecognized tax benefits. + References No definition available. + Details
Name: | unl_RecognizedInterestIncomeExpenseAndPenaltiesRelatedToUnrecognizedTaxBenefits
Namespace Prefix: | unl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | invest_InvestmentSecuritiesClassAxis=unl_RedemptionBasketsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |