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Schedule of Investments (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015
Collateral Amount On Open Futures Contracts	21,607,192usl_CollateralAmountOnOpenFuturesContracts
United States | US Treasury Securities | Cash Equivalents | U.S. Treasury Bills 0.05%, 7/9/2015
Interest rate	0.05%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities1Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	7/9/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.08%, 7/23/2015
Interest rate	0.08%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities2Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	7/23/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.06%, 7/30/2015
Interest rate	0.06%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities3Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	7/30/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.06%, 8/6/2015
Interest rate	0.06%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities4Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	8/6/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.07%, 8/13/2015
Interest rate	0.07%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities5Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	8/13/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.07%, 8/20/2015
Interest rate	0.07%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities6Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	8/20/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.07%, 8/27/2015
Interest rate	0.07%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities7Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	8/27/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.08%, 9/3/2015
Interest rate	0.08%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities8Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	9/3/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.10%, 9/10/2015
Interest rate	0.10%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities9Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	9/10/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.12%, 9/17/2015
Expiration date	9/17/2015
United States | US Treasury Securities | Cash Equivalents | U.S.Treasury Bills 0.11%, 9/24/2015
Interest rate	0.11%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DerivativeInstrumentRiskAxis = usl_UsTreasuryBillsSecurities11Member / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember
Expiration date	9/24/20
United States | U.S. Treasury Bill 0.10%, 6/25/2015 | US Treasury Securities | Cash Equivalents
Interest rate	0.10%us-gaap_DebtInstrumentInterestRateStatedPercentage / invest_InvestmentAxis = us-gaap_CashEquivalentsMember / invest_InvestmentGeographicRegionAxis = country_US / invest_InvestmentSecuritiesClassAxis = us-gaap_USTreasurySecuritiesMember / invest_InvestmentSecuritiesSeriesAxis = usl_UsTreasuryBillSecurities1Member
Expiration date	6/25/2015

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 6

-Subparagraph (SX 210.12-14.4(b))

-URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611322-123010



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 14

-Paragraph 4

-Subparagraph b

-Article 12



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 5

-Subparagraph (SX 210.12-13.5(d))

-URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611282-123010



Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

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